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Tuesday October 9th Today: Chapter 5 Return Exams Frequency: CD Classification of Matter Matter is organized by its components: elements, compounds, and mixtures. Ionic and Covalent Bonds Atoms form octets to become more stable. by losing, gaining, or sharing valence electrons. by forming ionic or covalent bonds. © 2013 Pearson Education, Inc. Chapter 5, Section 1 3 Covalent Compounds Covalent compounds are formed when nonmetals share valence electrons forming a covalent bond. Covalent compounds consist of molecules, which are discrete groups of atoms, such as: water, H2O carbon dioxide, CO2 glucose, C6H12O6 © 2013 Pearson Education, Inc. 2 H atoms + 1 O atom 1 C atom + 2 O atoms 6 C atoms + 12 H atoms + 6 O atoms Chapter 5, Section 1 4 Ionic Compounds Ionic compounds are formed when metal atoms transfer electrons to nonmetal atoms resulting in the formation of ionic bonds. Ionic compounds we use every day include: table salt NaCl baking soda NaHCO3 milk of magnesia Mg(OH)2 © 2013 Pearson Education, Inc. Chapter 5, Section 1 5 Ionic Compounds, Minerals Precious and semiprecious gemstones are also examples of ionic compounds called minerals. Sapphires and rubies are made of aluminum oxide (Al2O3), which is an ionic compound. Their brilliant colors come from the presence of other metals such as chromium, which make rubies red and iron and titanium, which make sapphires blue © 2013 Pearson Education, Inc. Chapter 5, Section 1 6 Octet Rule The octet rule is the tendency for atoms to share or transfer electrons to obtain a stable configuration of 8 valence electrons. Octet Rule The octet rule is associated with the stability of the noble gases except for He, which is stable with 2 valence electrons (duet). He 1s2 Valence Electrons 2 Ne 1s22s22p6 8 Ar 1s22s22p63s23p6 8 Metals Form Positive Ions Metals form positive ions called cations by a loss of their valence electrons. with the electron configuration of the nearest noble gas. that have fewer electrons than protons. Group 1A (1) metals ion 1+ Group 2A (2) metals ion 2+ Group 3A (3) metals ion 3+ © 2013 Pearson Education, Inc. Chapter 5, Section 1 9 Formation of a Sodium Ion, Na+ Sodium achieves an octet by losing its one valence electron. © 2013 Pearson Education, Inc. Chapter 5, Section 1 10 Formation of Magnesium Ion, Mg2+ Magnesium achieves an octet by losing its two valence electrons. © 2013 Pearson Education, Inc. Chapter 5, Section 1 11 Learning Check 1. What is the number of valence electrons in aluminum? A. 1 e– B. 2 e– C. 3 e– 2. What does aluminum require to acquire an octet of electrons? A. a loss of 3 e– C. a gain of 5 e– B. a gain of 3 e– 3. What is the charge of an aluminum ion? A. 3– B. 5– C. 3+ 4. What is the symbol for an aluminum ion? A. Al3+ B. Al3– C. Al+ Formation of Negative Ions In ionic compounds, nonmetals achieve an octet arrangement. gain electrons. form negatively charged ions called anions with 3–, 2–, or 1– charges. © 2013 Pearson Education, Inc. Chapter 5, Section 1 16 Formation of a Chloride Ion, Cl– Chlorine achieves an octet by adding one more electron to its 7 valence electrons. © 2013 Pearson Education, Inc. Chapter 5, Section 1 17 Charge of a Chloride Ion, Cl– By gaining one electron, the chloride ion has a 1− charge. charge © 2013 Pearson Education, Inc. Chapter 5, Section 1 18 Ionic Charge from Group Numbers Ions achieve the electron configuration of their nearest noble gas by forming positive ions with a charge equal to its Group number. Group 1A (1) = 1+ Group 2A (2) = 2+ Group 3A (3) = 3+ negative ions with a charge obtained by subtracting 8 or 18 from its Group number. Some Typical Ionic Charges Group Numbers for Some Positive and Negative Ions Learning Check 1. What is the Group number for sulfur? A. 4A (14) B. 8A (18) C. 6A (16) 2. What is the number of valence electrons in sulfur? A. 4 e− B. 6 e− C. 8 e− 3. To acquire an octet, what does sulfur require? A. gain of 2 e− B. loss of 2 e− C. a gain of 4 e− 4. What is the charge of sulfur ions? A. 2+ B. 2− C. 4− Ionic Compounds Ionic compounds consist of positive and negative ions. have attractive forces between the positive and negative ions called ionic bonds. have high melting and boiling points. are solid at room temperature. Formulas of Ionic Compounds The chemical formula of an ionic compound represents the element symbols and subscripts, which represent the lowest whole-number ratio of ions. In the formula of an ionic compound, the sum of positively and negatively charged ions is always zero. the charges are balanced. Charge Balance for NaCl, “Salt” In NaCl, a Na atom loses its valence electron. a Cl atom gains an electron. the symbol of the metal (sodium) is written first, followed by the symbol of the nonmetal (chlorine). © 2013 Pearson Education, Inc. Chapter 5, Section 1 28 Charge Balance In MgCl2 In MgCl2, a Mg atom loses two valence electrons. two Cl atoms gain one electron each. subscripts indicate the number of ions needed to give charge balance. the symbol of the metal (magnesium) is written first, followed by the symbol of the nonmetal (chlorine). © 2013 Pearson Education, Inc. Chapter 5, Section 1 29 Writing Ionic Formulas from Charge Balance Charge balance is used to write the formula for sodium nitride, a compound containing Na+ and N3−. © 2013 Pearson Education, Inc. Chapter 5, Section 1 30 Charge Balance in Na2S In sodium sulfide, Na2S, two Na atoms lose one valence electron each. one S atom gains two electrons. subscripts show the number of ions needed to give charge balance. The group of ions with the lowest ratio of ions in an ionic compound is called a formula unit . Formula from Ionic Charges Write the ionic formula of the compound containing Ba2+ and Cl−. Write the symbols of each ion. Ba2+ Cl− Balance the charges. Ba2+ Cl− (two Cl needed) Cl− Write the metal first, followed by the nonmetal, , using a subscript to represent the number of . Cl− ions. BaCl2 Learning Check Select the correct formula for each of the following ionic compounds. 1. Na+ and S2– A. NaS B. Na2S C. NaS2 2. Al3+ and Cl– A. AlCl3 B. AlCl C. Al3Cl 3. Mg2+ and N3– A. MgN B. Mg2N3 C. Mg3N2 Naming and Writing an Ionic Formula The name of an ionic compound is made up of 2 elements. has the name of the metal ion written first. has the name of the nonmetal ion written second using the first syllable of its element name. followed by ide. has a space separating the name of the metal and nonmetal. © 2013 Pearson Education, Inc. Chapter 5, Section 1 36 Charges of Representative Elements © 2013 Pearson Education, Inc. Chapter 5, Section 3 37 Naming Mg3N2 Step 1 Identify the cation and anion. The cation from Group 2A (2) is Mg2+, and the anion from Group 5A (15) is N3−. Step 2 Name the cation by its element name. Cation: Mg2+ is magnesium Step 3 Name the anion by using the first syllable of its element name followed by ide. Anion: nitrogen becomes nitride, N3− Step 4 Write the name for the cation first and the name for the anion second. Mg3N2 is magnesium nitride. Practice Naming • MgCl2 • Na2S • K3N