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10/12/2015 Chapter 6 Readiness Lecture Presentation Key Math Skills Chapter 6 Ionic and Molecular Compounds Karen C. Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chapter 6 Why do atoms react? • Using Positive and Negative Numbers in Calculations (1.4B) • Solving Equations (1.4D) Core Chemistry Skills • Writing Electron Configurations (4.7) • Drawing Lewis Symbols (4.8) Chapter 6 Why do atoms react? • Recall the chemical properties of the noble gases – they are extremely unreactive Completely filled valence energy level • What do they have in common that could be the cause of this lack of reactivity? • Examination of their electron configurations reveals that the noble gases either have 1. an outermost electron energy level that is completely filled with electrons (He = 2 e- in the 1st energy level, Ne = 8 e- in the 2nd energy level) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 8 valence electrons OR: 2. 8 electrons in the outermost energy level (8 valence e-) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chapter 6 Why do atoms react? 6.1 Ions: Transfer of Electrons • It is this arrangement of electrons that imparts stability to the noble gases Atoms form positively charged ions when they lose electrons and negatively charged ions when they gain electrons. • All other elements react in order to achieve the same electron configuration as their nearest noble gas neighbor (8 valence e- = octet rule) Ionic bonds are formed by the strong attractive forces between positive and negative ions. Learning Goal Write the symbols for the simple ions of the representative elements. • Atoms can gain, lose, or share electrons in order to achieve the same electronic structure as their nearest noble gas neighbor General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 1 10/12/2015 Ionic and Covalent Bonds Ionic and Covalent Bonds Chemical bonds are formed when atoms lose, gain, or share valence electrons to acquire an octet of eight valence electrons (octet rule). • Ionic bonds occur when valence electrons of a metal atom are transferred to the atom of a nonmetal. • Covalent bonds occur when nonmetal atoms share electrons to attain a noble gas arrangement. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Positive Ions: Metals Lose Electrons Positive Ions: Loss of Electrons In ionic bonding, ions form when atoms gain or lose their valence electrons to form a stable electron configuration. Metals in Group 1A (1), Group 2A (2), and Group 3A (13) Sodium atoms in Group 1A (1) are neutral, with 11 electrons and 11 protons, they • lose one electron to have the same number of valence electrons as neon and a filled energy level. • will form an ion with 10 electrons, 11 protons, and an ionic charge of 1+: Na+. • have low ionization energies, which means it doesn’t take much energy to remove an e• readily lose one or more of their valence electrons to form ions with a positive charge. • lose electrons until they have the same number of valence electrons as the nearest noble gas, usually eight valence electrons. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Positive Ions: Loss of Electrons Negative Ions: Nonmetals Gain Electrons Magnesium atoms in Group 2A (2) are neutral, and they have 12 electrons and 12 protons. They • will lose 2 electrons to have the same number of valence electrons as neon and a filled energy level. • form an ion with 10 electrons, 12 protons, and an ionic charge of 2+: Mg2+. Nonmetals, Group 5A (15), Group 6A (16), and Group 7A (17) • have high ionization energies, they don’t tend to lose electrons but instead gain electrons • readily gain one or more valence electrons to form ions with a negative charge. • gain electrons until they have the same number of valence electrons as the nearest noble gas, usually eight valence electrons. Core Chemistry Skill Writing Symbols For Positive and Negative Ions General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 2 10/12/2015 Negative Ions: Gain of Electrons Formulas, Names of Common Ions Chlorine atoms in Group 7A (17) are neutral, and they have 17 electrons and 17 protons. They • will gain one electron to have the same number of valence electrons as argon. • form an ion with 18 electrons, 17 protons, and a charge of 1−: Cl−. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Ionic Charges, Group Numbers General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Chemistry Link to Health: Important Ions in the Body We can use the group numbers in the periodic table to determine the charges for the ions of the representative elements. Ions are important in regulating body functions. Ion Occurrence Function Source Na+ Principal cation outside the cell Regulation and control of body fluids Salt, cheese, pickles K+ Principal cation outside the cell Regulation of body fluids and cellular functions Bananas, potatoes, orange juice, milk Ca2+ Cation outside the Major cation in bones, cell; found in bones needed for muscle contractions Mg2+ Cation outside the Essential for certain cell; found in bones enzymes, muscles, and nerve control General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Milk, yogurt, cheese, greens, spinach Chlorophyll, nuts, grains © 2016 Pearson Education, Inc. Study Check Study Check Write the formula and symbol of an ion with 16 protons and 18 electrons. Consider the elements calcium and chlorine. A. Identify each as a metal or a nonmetal. B. State the number of valence electrons for each. C. State the number of electrons that must be lost or gained for each to acquire an octet. D. Write the symbol, including its ionic charge, and name of each resulting ion. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 3 10/12/2015 6.2 Writing Formulas for Ionic Compounds Properties of Ionic Compounds Ionic compounds consist of positive and negative charges held together by the strong electrical attractions between oppositely charged ions. Ionic compounds • consist of positive and negative ions. • have attractions called ionic bonds between positively and negatively charged ions. • have high melting points. • are solids at room temperature. Learning Goal Using charge balance, write the correct formula for an ionic compound. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. NaCl, An Ionic Compound Formulas of Ionic Compounds Sodium chloride is more commonly known as table salt. The magnification of NaCl crystals shows the arrangement of Na+ and Cl− ions in an NaCl crystal. In a chemical formula, • the symbols and subscripts are written in the lowest whole-number ratio of the atoms or ions. • the sum of ion charges equals zero. • the total positive charge = total negative charge. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Subscripts in Formulas General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Writing Ionic Formulas from Ion Charges To balance ionic charge in an ionic compound, total positive charge = total negative charge Core Chemistry Skill Writing Ionic Formulas General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 4 10/12/2015 Study Check Study Check Write the ionic formula of the compound formed with Ba2+ and Cl− ions. Select the correct formula for each of the following ionic compounds. 1. Na+ and O2− A. NaO B. Na2O C. NaO2 2. Al3+ and Cl− A. AlCl3 B. AlCl C. Al3Cl 3. Mg2+ and N3− A. MgN B. Mg2N3 C. Mg3N2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 6.3 Naming and Writing Ionic Compounds Naming Ionic Compounds Iodized salt contains Kl, potassium iodide, to prevent iodine deficiency. When naming an ionic compound, • the name of the metal is written first and is the same as the name of the element. • the name of the nonmetal is the first syllable of the nonmetal name + ide ending and is written second. • a space is placed between the name of the metal and nonmetal ion. Learning Goal Given the formula of an ionic compound, write the correct name; given the name of an ionic compound, write the correct formula. Core Chemistry Skill Naming Ionic Compounds General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Names of Some Ionic Compounds General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Guide to Naming Ionic Compounds © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 5 10/12/2015 Naming Ionic Compounds, K2O Naming Ionic Compounds, K2O Name the ionic compound K2O. STEP 1 Identify the cation and anion. The cation, K+, is from Group 1A (1), and the anion, O2−, is from Group 6A (16). STEP 2 Name the cation by its element name. The cation, K+, is potassium. Name the ionic compound K2O. STEP 3 Name the anion by using the first syllable of its element name followed by ide. The name of the anion is oxide. STEP 4 Write the name for the cation first and the name for the anion second. K2O is potassium oxide. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Study Check Solution Write the names of the following compounds. A. CaO ___________ B. Al2O3 ___________ C. MgCl2 ___________ Write the names of the following compounds. © 2016 Pearson Education, Inc. STEP 1 Identify the cation and anion. A. CaO: The cation, Ca2+, is from Group 2A (2), and the anion, O2−, is from Group 6A (16). B. Al2O3: The cation, Al3+, is from Group 3A (13), and the anion, O2−, is from Group 6A (16). C. MgCl2: The cation, Mg2+, is from Group 2A (2), and the anion, Cl−, is from Group 7A (17). General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Solution Write the names of the following compounds. Write the names of the following compounds. STEP 2 Name the cation by its element name. A. CaO: The cation, Ca2+, is calcium. STEP 3 Name the anion by using the first syllable of its element name followed by ide. A. CaO: The anion, O2−, is oxide. B. Al2O3: The cation, Al3+, is aluminum. B. Al2O3: The anion, O2−, is oxide. C. MgCl2: The cation, Mg2+, is magnesium. C. MgCl2: The anion, Cl−, is chloride. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 6 10/12/2015 Solution Study Check Write the names of the following compounds. Write the formulas and names for compounds of the following ions: Br− S2− N3− STEP 4 Write the name of the cation first and the name of the anion second. A. The name of CaO is calcium oxide. Na+ B. The name of Al2O3 is aluminum oxide. Al3+ C. The name of MgCl2 is magnesium chloride. © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Metals with Variable Charge General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Metals with Variable Charge Transition metals except for Zn2+, Cd2+, and Ag+ form two or more positive ions (cations). A Roman numeral equal to the ion charge is placed in parentheses immediately after the metal name. Cu2+ Cu+ Fe2+ Fe3+ copper(II) copper(I) iron(II) iron(III) Pb2+ Pb4+ Cr2+ Cr3+ lead(II) lead(IV) chromium(II) chromium(III) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Determination of Variable Charge General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Ion Charges, Periodic Table Use the charge on the anion and charge balance to calculate charge on the metal ion. MnF2 Mn charge + 2 F− charge = 0 ? + 2 (1−) = 0 2+ + 2− =0 Manganese(II) fluoride General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 7 10/12/2015 Guide to Naming Ionic Compounds with Variable Charge Metals Naming Ionic Compounds with Variable Charge Metals, FeCl2 Name the ionic compound FeCl2. STEP 1 Determine the charge of the cation from the anion. Formula ANALYZE THE Elements PROBLEM Groups Ions Charge Balance Ions © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Naming Ionic Compounds with Variable Charge Metals, FeCl2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Metal FeCl2 iron (Fe) chloride transition element Fe? Fe? + 1(?) + 2+ Fe Nonmetal (Cl) Group 7A (17) Cl− 2(1−) = 0 2(1−) = 0 Cl− © 2016 Pearson Education, Inc. Study Check Name the following ionic compound containing a variable charge metal. SnO2 Name the ionic compound FeCl2. STEP 2 Name the cation by its element name, and use a Roman numeral in parentheses for the charge. iron(II) STEP 3 Name the anion by using the first syllable of its element name followed by ide. chloride STEP 4 Write the name for the cation first and the anion second. iron(II) chloride © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Solution Name the following ionic compound containing a variable charge metal. SnO2 Name the following ionic compound containing a variable charge metal. SnO2 STEP 1 Determine the charge of the cation from the anion. STEP 2 Name the cation by its element name and use a Roman numeral in parentheses for the charge. tin(IV) STEP 3 Name the anion by using the first syllable of its element name followed by ide. oxide STEP 4 Write the name for the cation first and the anion second. tin(IV) oxide ANALYZE THE PROBLEM Formula Elements Groups Ions Charge Balance Ions General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Metal SnO2 tin (Sn) transition element Sn? Sn? + 1(?) + Sn4+ Nonmetal oxide (O) Group 6A (16) O2− 2(2−) = 0 2(2−) = 0 O2− © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 8 10/12/2015 Writing Formulas from the Name of an Ionic Compound Guide to Writing Formulas from the Name of an Ionic Compound The formula for an ionic compound is written from, • the first part of the name that describes the metal ion. • the second part of the name that specifies the nonmetal ion. Subscripts are added to balance the charge. © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Writing Formulas from the Name of an Ionic Compound Writing Formulas from the Name of an Ionic Compound Write the formula for iron(III) chloride. Write the formula for iron(III) chloride. STEP 1 Identify the cation and anion. STEP 2 Balance the charges. Fe3+ Cl− Cl− Cl− 1(3+) + 3(1−) = 0 ANALYZE THE PROBLEM Type of Ion Name Group Symbol of Ion General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Cation iron(III) transition element Fe3+ Anion chloride Group 7A (17) Cl− © 2016 Pearson Education, Inc. Becomes the subscript in the chemical formula. STEP 3 Write the formula, cation first, using subscripts from the charge balance. FeCl3 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Solution Write chemical formulas for the following compounds: A. nickel(II) sulfide B. zinc chloride C. iron(III) oxide Write chemical formulas for the following compounds. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. STEP 1 Identify the cation and anion. A. nickel(II) sulfide The Roman numeral (II) indicates that the charge on the nickel ion is 2+, Ni2+. The anion sulfide S2−. B. zinc chloride Zinc is one of the transition metals with a fixed charge of 2+, Zn2+. The anion chloride is Cl−. C. iron(III) oxide The Roman numeral (III) indicates that the charge on the iron ion is 3+, Fe3+. The anion oxide is O2−. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 9 10/12/2015 Solution Solution Write chemical formulas for the following compounds. Write chemical formulas for the following compounds. STEP 2 Balance the charges. A. nickel(II) sulfide Ni2+ S2− 1(2+) + 1(2−) = 0 STEP 3 Write the formula, cation first, using subscripts from the charge balance. A. nickel(II) sulfide NiS B. zinc chloride ZnCl2 C. iron(III) oxide Fe2O3 B. zinc chloride Zn2+ Cl− Cl− 1(2+) + 2(1−) = 0 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake C. iron(III) oxide Fe3+ O2− Fe3+ O2− O2− 2(3+) + 3(2−) = 0 © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 6.4 Polyatomic Ions Polyatomic Ions Sodium chlorite, NaClO2, is used in the processing and bleaching of pulp from wood fibers and recycled cardboard. Polyatomic ions • are a group of atoms with an overall charge. • often consist of a nonmetal such as phosphorus, sulfur, carbon, or nitrogen and oxygen. • usually have a 1−, 2−, or 3− charge. • have a negative charge, except for NH4+, ammonium, which has a positive charge, Learning Goal Write the name and formula for an ionic compound containing a polyatomic ion. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Polyatomic Ions General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Polyatomic Ions, Names, and Formulas Many products contain polyatomic ions, which are groups of ions that have an ionic charge. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 10 10/12/2015 Names of Polyatomic Ions Names of Polyatomic Ions 1. Names of most common polyatomic ions end in ate. SO42− sulfate PO43− phosphate NO3− nitrate 3. Exceptions to these rules are the following: cyanide CN− OH− hydroxide 2. When a related ion has one less oxygen, its name ends in ite. SO32− sulfite PO33− phosphite NO2− nitrite © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Names of Polyatomic Ions 5. Halogens form 4 polyatomic ions with oxygen. Each has a −1 charge. ClO4− perchlorate ClO3− chlorate ClO2− chlorite ClO− hypochlorite 4. Add an H+ to the polyatomic + H+ = CO32− carbonate + H+ = SO42− + H+ = sulfate + H+ = ion, and add +1 to its charge. HCO3− bicarbonate or hydrogen carbonate HSO4− bisulfate or hydrogen sulfate © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Writing Formulas for Compounds Containing Polyatomic Ions When writing formulas for ionic compounds containing polyatomic ions, we use the same rules of charge balance as those for simple ionic compounds. Consider the formula for magnesium nitrate: Sodium chlorite is used in the processing and bleaching of pulp from wood fibers and recycled cardboard. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Guide to Writing Formulas with Polyatomic Ions Magnesium ion Nitrate ion Mg2+ + (2+) Mg2+ + + NO3− NO3− 2(1−) 2 NO3− Parentheses are placed around the polyatomic ion, and the subscript is placed just outside the parentheses. = 0 = Mg(NO3)2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Writing Formulas with Polyatomic Ions, Aluminum Bicarbonate Write the formula for aluminum bicarbonate. STEP 1 Identify the cation and polyatomic ion (anion). Cation Polyatomic ion Al3+ HCO3− STEP 2 Balance the charges. Al3+ HCO3− HCO3− HCO3− 1(3+) + 3(1−) = 0 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 11 10/12/2015 Writing Formulas with Polyatomic Ions, Aluminum Bicarbonate Study Check Write the formula for sodium phosphate. Write the formula for aluminum bicarbonate. STEP 3 Write the formula, cation first, using the subscripts from charge balance. Al(HCO3)3 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Solution Write the formula for sodium phosphate. Write the formula for sodium phosphate. STEP 1 Identify the cation and polyatomic ion (anion). Cation Polyatomic ion Na+ PO43− STEP 2 Balance the charges. Na+ PO43− Na+ Na+ 3(1+) + 1(3−) = 0 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Naming Compounds with Polyatomic Ions STEP 3 Write the formula, cation first, using the subscripts from charge balance. Na3PO4 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Compounds with Polyatomic Ions When naming ionic compounds containing polyatomic ions, • first write the positive ion, usually a metal. • write the name of the polyatomic ion second. Recognizing polyatomic ions in a chemical formula helps to name it correctly. As with other ionic compounds, no prefixes are used. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 12 10/12/2015 Study Check Guide to Naming Compounds with Polyatomic Ions Select the correct formula for each. 1. aluminum nitrate A. AlNO3 B. Al(NO) 3 C. Al(NO3) 3 2. copper(II) nitrate A. CuNO3 B. Cu(NO3)2 C. Cu2 (NO3) 3. iron(III) hydroxide A. FeOH B. Fe3OH C. Fe(OH)3 4. tin(IV) hydroxide B. Sn(OH)2 C. Sn4(OH) A. Sn(OH)4 © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Flow Chart, Naming Ionic Compounds General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Name the following ionic compounds: A. Ca(NO3)2 B. FePO4 © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Solution Ca2+ B. FePO4 Fe3+ © 2016 Pearson Education, Inc. Study Check Name the following ionic compounds: STEP 1 STEP 2 STEP 3 Identify Name Name cation/anion cation anion A. Ca(NO3)2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake NO3− PO4 3− General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake STEP 4 Name compound Name each of the following compounds containing polyatomic ions. A. MgSO3 calcium nitrate B. MgSO4 calcium nitrate iron(III) phosphate iron(III) phosphate © 2016 Pearson Education, Inc. C. Pb3(PO3)2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 13 10/12/2015 Study Check 6.5 Molecular Compounds: Sharing Electrons Name each of the following compounds: A. Fe2(SO4)3 B. Ba3(PO3)2 C. NiCO3 The names of molecular compounds need prefixes because several different compounds can be formed from the same two nonmetals. Learning Goal Given the formula of a molecular compound, write its correct name; given the name of a molecular compound, write its formula. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Covalent Bonds © 2016 Pearson Education, Inc. Names and Formulas, Molecular Compounds Molecular compounds form when • atoms of two or more nonmetals share electrons and form a covalent bond. • valence electrons are shared by nonmetal atoms to achieve stability. A molecule forms when two or more atoms share electrons. Core Chemistry Skill Writing the Names and Formulas for Molecular Compounds General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Names and Formulas, Molecular Compounds When naming a molecular compound, the • first nonmetal in the formula is named by its element name. • second nonmetal is named using the first syllable of the name followed by ide. When a subscript indicates two or more atoms of an element, a prefix is shown in front of its name. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Common Molecular Compounds Several compounds may be formed from the same two nonmetals: CO2 = carbon dioxide CO = carbon monoxide • The number of oxygen atoms present is indicated by the prefix. • When the vowels o and o or a and o appear together, the first vowel is omitted. NO = nitrogen monoxide, General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 14 10/12/2015 Guide to Naming Molecular Compounds Naming Molecular Compounds, NCl3 Name the molecular compound NCl3. ANALYZE THE PROBLEM Symbol of the Element Name Subscript Prefix N nitrogen 1 none Cl chloride 3 tri STEP 1 Name the first nonmetal by its element name. In NCl3, the first nonmetal (N) is nitrogen. © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Naming Molecular Compounds, NCl3 Study Check Name the molecular compound NCl3. Name the molecular compound B2O3. © 2016 Pearson Education, Inc. STEP 2 Name the second nonmetal by using the first syllable of the element name followed by ide. In NCl3, the second nonmetal (Cl) is chloride. STEP 3 Add prefixes to indicate the number of atoms (subscripts). Because there is one nitrogen atom, no prefix is needed. The subscript 3 for the Cl atoms is shown as the prefix tri. The name of NCl3 is nitrogen trichloride. © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Solution Solution Name the molecular compound B2O3. Name the molecular compound B2O3. ANALYZE THE PROBLEM Symbol of the Element Name Subscript Prefix B boron 2 di O oxide 3 tri STEP 1 Name the first nonmetal by its element name. In B2O3, the first nonmetal (B) is boron. STEP 2 Name the second nonmetal by using the first name followed by ide. The name of the second nonmetal (O) is oxide. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. STEP 3 Add prefixes to indicate the number of atoms (subscripts). In B2O3, the first nonmetal (B) has the subscript of 2, which is shown as the prefix di. The subscript of 3 for the O atoms is shown as the prefix tri. The name of B2O3 is diboron trioxide. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 15 10/12/2015 Guide to Writing Formulas from the Names of Molecular Compounds Study Check Write the molecular formula for diphosphorus pentoxide. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Compounds, Ionic or Covalent? Write the molecular formula for diphosphorus pentoxide. A compound is usually • ionic if the first element in the formula or the name is a metal or the polyatomic ion NH4+. K2O: K is a metal; the compound is ionic. potassium oxide • covalent if the first element in the formula is a nonmetal. N2O: N is a nonmetal; the compound is covalent. dinitrogen oxide STEP 1 Write the symbols in the order of the elements in the name. STEP 2 Write any prefixes as subscripts. The prefix di in diphosphorus indicates there are two phosphorus atoms. The prefix penta in pentoxide indicates there are five oxygen atoms. P2O5 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Flowchart, Naming Compounds General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Select the correct name for each compound. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 1. SiCl4 A. silicon chloride B. tetrasilicon chloride C. silicon tetrachloride 2. P2O5 A. phosphorus oxide B. phosphorus pentoxide C. diphosphorus pentoxide 3. Cl2O7 A dichlorine heptoxide B. dichlorine oxide C. chlorine heptoxide General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 16 10/12/2015 Study Check 6.6 Lewis Structures for Molecules and Polyatomic Ions Identify each compound as ionic or covalent and give its correct name. A. SO3 B. BaCl2 C. (NH4)3PO3 Learning Goal Draw the Lewis structures for molecular compounds or polyatomic ions. D. Cu2CO3 E. N2O4 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake A molecule is represented by a Lewis structure in which the valence electrons of all the atoms are arranged to give octets. © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. The Simplest Molecule, H2 Formation of H2 Molecule A hydrogen molecule, H2, • forms as the atoms move closer and the positive charge of the nucleus attracts the electron of the other atom. • has a shared pair of electrons, a covalent bond, to give a noble gas arrangement of He to each H atom. • forms when the molecule formed is more stable than the two individual H atoms. A covalent bond forms as H atoms move close together to share electrons. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Lewis Structures, Molecules Lewis Structures, Molecules A molecule is represented by a Lewis structure in which the valence electrons of all the atoms are arranged to give octets. • The shared electrons, or bonding pairs, are shown as two dots or a single line between atoms. • The nonbonding pairs, or lone pairs, are placed on the outside of the atoms. A molecule is represented by a Lewis structure in which the valence electrons of all the atoms are arranged to give octets. To draw the electron-dot formula for a fluorine molecule, F2, • we start with the electron-dot symbols for each fluorine atom. • each fluorine atom shares one electron to form a covalent bond, giving each fluorine an octet. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 17 10/12/2015 Elements, Diatomic Molecules Sharing Electrons Between Atoms of Different Elements The elements hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine exist as diatomic molecules. The number of electrons a nonmetal atom shares and the number of covalent bonds it forms are usually equal to the number of electrons it needs to achieve a stable electron configuration. Typical Bonding Patterns of Some Nonmetals Core Chemistry Skill Drawing Lewis Structures General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Drawing Lewis Structures Molecules, Lewis Structures To draw the electron-dot formula for methane, CH4, • draw the Lewis symbols for carbon and hydrogen. Electron-dot formulas for common molecules such as methane, ammonia, and water are shown in Table 6.13. • carbon needs four hydrogen atoms to have an octet. • two bonding electrons between carbon and hydrogen can be drawn as a line. © 2016 Pearson Education, Inc. • the central atom is the atom in the formula with the least number of atoms. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Guide to Drawing Electron-Dot Formulas General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Draw the Lewis structure for PCl3, phosphorus trichloride, which is used in the preparation of pesticides and flame retardants. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 18 10/12/2015 Solution Solution Draw the Lewis structure for PCl3, phosphorus trichloride, which is used in the preparation of pesticides and flame retardants. Draw the Lewis structure for PCl3, phosphorus trichloride, which is used in the preparation of pesticides and flame retardants. STEP 1 Determine the arrangement of atoms. In PCl3, P is the central atom; there is only one phosphorus atom in the formula. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. STEP 2 Determine the total number of valence electrons. Use the group number to determine the number of valence electrons for each element. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Solution Draw the Lewis structure for PCl3, phosphorus trichloride, which is used in the preparation of pesticides and flame retardants. Draw the Lewis structure for PCl3, phosphorus trichloride, which is used in the preparation of pesticides and flame retardants. STEP 3 Attach each bonded atom to the central atom with a pair of electrons. Each bonding pair can be represented with a single line. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. STEP 4 Place the remaining electrons using single or multiple bonds to complete octets (two for H). Six electrons (3 × 2 e−) are used to bond the central P atom to three Cl atoms. Twenty valence electrons are left. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Double and Triple Bonds Exceptions to the Octet Rule A double bond • occurs when atoms share two pairs of electrons. • forms when there are not enough electrons to complete octets. A triple bond • occurs when atoms share three pairs of electrons. • forms when there are not enough electrons to complete octets. While the octet rule is useful, there are exceptions. • Hydrogen requires just 2 electrons to form a noble gas arrangement. • Nonmetals P, S, Cl, Br, and I can form compounds with 10 or 12 valence electrons. • The S atom has an octet in many compounds, but in SF6, there are 12 valence electrons or 6 bonds to the sulfur atom. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 19 10/12/2015 6.7 Electronegativity and Bond Polarity Electronegativity The electronegativity values of representative elements in Group 1A (1) to Group 7A (17). The electronegativity of an atom is its ability to attract the shared electrons in a bond. It • increases from left to right going across a period on the periodic table. • increases from the bottom to the top of the periodic table. • is high for the nonmetals, with fluorine as the highest. • is low for the metals. Learning Goal Use electronegativity to determine the polarity of a bond. Core Chemistry Skill Using Electronegativity © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Electronegativity and the Periodic Table © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Polarity of Bonds The difference in electronegativity of bonding atoms can be used to predict the polarity of the bond. In the H2 molecule, electrons are shared equally and the bond is nonpolar. In the HCl molecule, electrons are shared unequally, and the bond is polar. © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Nonpolar Covalent Bonds Polar Covalent Bonds A nonpolar covalent bond occurs between nonmetals. It • is an equal or almost equal sharing of electrons by the two bonding atoms. • has a very small electronegativity difference between atoms. A polar covalent bond occurs between nonmetal atoms. It • is an unequal sharing of electrons. • has a moderate electronegativity difference. Examples Examples Atoms N-N Cl-Br H-Si Electronegativity Difference 3.0 − 3.0 = 0.0 3.0 − 2.8 = 0.2 2.1 − 1.8 = 0.3 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Type of Bond Nonpolar covalent Nonpolar covalent Nonpolar covalent © 2016 Pearson Education, Inc. Atoms O-Cl Cl-C O-S Electronegativity Difference 3.5 − 3.0 = 0.5 3.0 − 2.5 = 0.5 3.5 − 2.5 = 1.0 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Type of Bond Polar covalent Polar covalent Polar covalent © 2016 Pearson Education, Inc. 20 10/12/2015 Dipoles and Bond Polarity Ionic Bonds A polar covalent bond becomes more polar as the difference in electronegativity increases. The separation of charges in a polar bond is called a dipole. The positive and negative ends of the dipole are located by using • the lowercase Greek letter delta with a positive or negative charge. • an arrow that points from the positive to the negative end of the dipole. An ionic bond • occurs between metal and nonmetal ions. • is a result of electron transfer. • has a large electronegativity difference (1.8 or more). Examples Atoms Cl-K N-Na S-Cs General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Variations in Bonding Electronegativity Difference 3.0 – 0.8 = 2.2 3.0 – 0.9 = 2.1 2.5 – 0.7 = 1.8 Type of Bond Ionic Ionic Ionic General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Electronegativity and Bond Types The difference in electronegativity values for two atoms can be used to predict the type of chemical bond. If the electronegativity difference is • between 0 and 0.4, the bond is nonpolar covalent. • between 0.5 and 1.8, the bond is polar covalent. • greater than 1.8, the bond is ionic and the electrons are considered transferred. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Predicting Bond Type Using Electronegativity General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Use the electronegativity difference to identify the type of bond (nonpolar covalent [NP], polar covalent [P], or ionic [I]) between the following: A. K—N B. N—O C. Cl—Cl D. H—Cl General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 21 10/12/2015 6.8 Shapes and Polarity of Molecules VSEPR Theory In a molecule of methane, CH4, the central C atom is bonded to four H atoms. The best geometry for minimal repulsion is tetrahedral, with bond angles of 109°. Valence Shell Electron-Pair Repulsion Theory (VSEPR) • describes the orientation of electron groups around the central atom. • states that electron groups are arranged as far apart as possible around the central atom. • states that the specific shape of a molecule is determined by the number of atoms attached to the central atom. Learning Goal Predict the three-dimensional structure of a molecule, and classify it as polar or nonpolar. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Core Chemistry Skill Predicting Shape General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Central Atoms with Two Electron Groups Central Atoms with Three Electron Groups In a molecule of CO2 • two electron groups are placed around the central atom, carbon. • the repulsion is minimized by placing the two groups on opposite sides of the carbon atom, giving this a linear arrangement with bond angles of 180°. • the shape with two electron groups around the central atom is linear. In a molecule of formaldehyde, H2CO3, • three electron groups are placed around the central atom, carbon. • the repulsion is minimized by placing the three groups as far apart as possible at bond angles of 120°. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. • the shape with three electron groups around the central atom is trigonal planar. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Central Atoms with Three Electron Groups Central Atoms with Four Electron Groups In a molecule of SO2, there are three electron groups around the central atom S: 1. a single-bonded O atom 2. a double-bonded O atom 3. a lone pair of electrons • The repulsion is minimized by placing the three electron groups as far apart as possible. • The shape with two bonds and a lone pair on the central atom is bent with a bond angle of 120°. In a molecule of CH4 • four electron groups are attached to H atoms around the central atom, carbon. • the repulsion is minimized by placing the four electron groups at corners of a tetrahedron with bond angles of 109°. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. • the shape with four bonds on the central atom is called tetrahedral. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 22 10/12/2015 Central Atoms with Four Electron Groups Central Atoms with Four Electron Groups In a molecule of NH3 • four electron groups, three bonds to H atoms and one lone pair, are around the central atom, N. • the repulsion is minimized by placing the four electron groups at corners of a tetrahedron with bond angles of 109°. In a molecule of H2O • four electron groups, two bonds to H atoms and two lone pairs, are around the central atom, O. • the repulsion is minimized by placing the four electron groups at corners of a tetrahedron with bond angles of 109°. • the shape with three bonds and a lone pair on the central atom is called trigonal pyrimidal. • the shape with two bonds and two lone pairs on the central atom is called bent. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Molecular Shapes, Electron-Groups General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Guide to Predicting Molecular Shape General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Predict Molecular Shape of H2S Predict Molecular Shape of H2S Predict the shape of a molecule of H2S. Predict the shape of a molecule of H2S. STEP 1 Draw the Lewis structure. STEP 3 Use the atoms bonded to the central atom to determine the shape. The central atom S has two bonds and two lone pairs. The shape is bent, 109°. STEP 2 Arrange electron groups around the central atom to minimize repulsion. To minimize repulsion, electron groups have a tetrahedral arrangement. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 23 10/12/2015 Study Check Solution State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. A. PF3 STEP 1 Draw the Lewis structure. B. H2O C. CCl4 A. PF3 B. H2O O C. CCl4 H H General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Solution State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. STEP 2 Arrange electron groups around the central atom to minimize repulsion. A. PF3: To minimize repulsion, the electron groups would have a tetrahedral arrangement. B. H2O: To minimize repulsion, the electron groups would have a tetrahedral arrangement. C. CCl4: To minimize repulsion, the electron groups would have a tetrahedral arrangement. STEP 3 Use the atoms bonded to the central atom to determine the molecular shape. A. PF3: With three bonds and one lone pair on the central atom, the shape is trigonal pyrimidal. B. H2O: With two bonds and two lone pairs on the central atom, the shape is bent. C. CCl4: With four bonds on the central atom, the shape is tetrahedral. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Polarity of Molecules Polarity of Molecules Nonpolar molecules • such as H2, Cl2, and O2 are nonpolar because they contain nonpolar bonds. Polar molecules such as HCl are polar because • one end of the molecule is more negatively charged than the other. • the polar bonds in the molecule do not cancel each other. • the electrons are shared unequally in the polar covalent bond. • with polar bonds can be nonpolar if the polar bonds (dipoles) cancel in a symmetrical arrangement, such as in CO2 and CF4. Core Chemistry Skill Identifying Polarity of Molecules General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 24 10/12/2015 Polarity of Molecules Polarity of Molecules In a polar molecule such as H2O, there • are two lone pairs and two bonds around the central atom. • are dipoles that do not cancel since the shape is bent, making the molecule positive at one end and negative at the other end. • is a partial negative charge on the central atom. In a polar molecule such as NH3, there • is one lone pair and three bonds around the central atom. • are dipoles that do not cancel since the shape is trigonal pyramidal, making the molecule positive at one end and negative at the other end. • is a partial negative charge on the central atom. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Guide to Determining the Polarity of a Molecule © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Determination of Polarity Determine if the molecule OF2 is polar or nonpolar. STEP 1 Determine if the bonds are polar covalent or nonpolar covalent. O (3.5) and F (4.0) give an electronegativity difference of 0.5, which makes the bonds polar covalent. STEP 2 If the bonds are polar covalent, draw the Lewis structure and determine if the dipoles cancel. OF2 is a polar molecule. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. O F F © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Study Check Solution Identify each of the following molecules as polar or nonpolar. A. PBr3 B. HBr Identify each of the following molecules as polar or nonpolar. STEP 1 STEP 2 Bonds, polar or Draw molecule to see if nonpolar any polar bonds cancel A. PBr3 P = 2.1 P Br = 2.8, polar polar Br Br Br C. CH4 B. HBr H = 2.1 Br = 2.8, polar polar H Br C. CH4 C = 2.5 H = 2.1, nonpolar nonpolar H C H General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake H H © 2016 Pearson Education, Inc. 25 10/12/2015 6.9 Attractive Forces in Compounds Dipole-Dipole, Hydrogen Bonds The protein shape is stabilized by attractive forces between functional groups of side chains (R groups) on the amino acids, causing it to twist and bend into a specific three-dimensional shape. In covalent compounds, polar molecules • exert attractive forces called dipole-dipole attractions. • form strong dipole attractions called hydrogen bonds between hydrogen atoms bonded to F, O, or N, and a lone pair on F, O, or N. Hydrogen bonds are the strongest force between molecules and play a major role in the shape of DNA. Learning Goal Describe the attractive forces between ions, polar covalent molecules, and nonpolar covalent molecules. Core Chemistry Skill Identifying Attractive Forces General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Dispersion Forces Melting Points and Attractive Forces Dispersion forces are • weak attractions between nonpolar molecules. • caused by temporary dipoles that develop when molecules bump into each other. • weak but make it possible for nonpolar molecules to form liquids and solids. Melting points of compounds • are related to the strength of attractive forces between molecules or compounds. • are lower due to weak forces such as dispersion forces. • are higher due to stronger attractive forces such as hydrogen bonding. • are highest in ionic compounds due to the strong attractive forces between ions in the compound. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Melting Points and Attractive Forces General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Comparison of Bonding and Attractive Forces General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 26 10/12/2015 Study Check Chemistry Link to Health: Attractive Forces, Proteins Identify the main type of attractive forces that are present in liquids of the following compounds: ionic bonds, dipole-dipole, hydrogen bonds, or dispersion forces. A. NCl3 B. H2O C. Br-Br D. KCl E. NH3 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Proteins are biological molecules with many different functions. They are needed for • structural components such as cartilage, muscles, hair. • the formation of enzymes that regulate biological reactions. • myoglobin and hemoglobin, which transport oxygen in blood and muscle. © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Chemistry Link to Health: Attractive Forces, Proteins Chemistry Link to Health: Attractive Forces, Proteins Proteins are composed of building blocks called amino acids. Every amino acid has a central carbon atom bonded to • an –NH3+, from an amine. • a –COO−, from a carboxylic acid. • an H atom. • an R group, which is unique for each amino acid. Several amino acids have R groups or side chains that contain • an amide group, –CONH2. • a hydroxyl, – OH, group. • a carboxyl, –COOH, group ionized as carboxylate, –COO−. • an amine, –NH2, group ionized as ammonium, –NH3+. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chemistry Link to Health: Attractive Forces, Proteins Chemistry Link to Health: Attractive Forces, Proteins The primary structure of a protein is its sequence of amino acids. It is the sequence of amino acids that determines the protein’s function. Proteins have a higher level of structure that is determined by the attractive forces between the amino acids. Amino acids in a protein are linked by a peptide bond between the COO− of one amino acid and the –NH3+ of the next amino acid. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. When hydrogen bonds form between a hydrogen atom in an N—H group and the oxygen of the C═O group, the protein forms an alpha helix. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake H-bonds can form between the –OH of serine and the –NH2 of asparagine. © 2016 Pearson Education, Inc. 27 10/12/2015 Chemistry Link to Health: Attractive Forces, Proteins Hydrogen bonds can also form between the polar side chains of the amino acids on the outside of the protein and the –OH and –H of polar water molecules in the external aqueous environment. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Concept Map Attractive forces hold the protein in a specific shape. © 2016 Pearson Education, Inc. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 28