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Transcript
Unit: Chemical Bonding I. Compound • Pure substances - has 2 or more elements chemically combined – Water (H2O) – Salt (NaCl) – Oxygen (O2 ) – Sugar Sucrose (C12H22O11) A. Different Combinations of elements produce different substances • H2O Water • H2O2 Peroxide • O2 Oxygen • O3 Ozone B. Compound has new set of properties • The individual elements that make up the compound lose their own properties • • • H gas, combustible O gas, supports combustion H O liquid, clear, extinguishes a flame 2 2 2 B. Compound has new set of properties • • • Na Reactive, solid metal Cl2 poisonous green gas NaCl table salt C. Atoms form compounds when the compound is more stable than the separate atoms. • Noble gases Chemically stable – 8 valence e-’s • Elements w/out 8 valence electrons more stable in compounds •Atoms can lose, gain, or share electrons to become stable •A chemical bond is the force that hold atoms together in a compound III. Chemical Formulas • Shorthand way to represent chemical compounds • use chemical symbols combined to make compound • ex. H2 O Subscript Subscripts • The # represents the number of atoms of the previous element that are in one molecule of the compound • If there is NO subscript after the element, then “ 1 ” is understood to be there – “1” is never written!!!! How many atoms of each element are in these ? 1. C6H12O6 2. CaCl2 3. Mg(OH)2 4. Ca(H2PO4)2 IV. Electron Dot Diagrams (Lewis Dot diagrams) Use element’s Valence electrons electrons in outer shell • Write elements chemical symbol • Use a dot to represent valence e-’s • Place valence e-’s around symbol • **Hint: Like you would sit at the dinner table Electron Dot Diagrams • Sulfur Neon Chlorine V. Octet Rule • Atoms are very stable with 8 valence electrons – ( 4 pairs) • atoms wants to have a full octet by either gaining, losing, or sharing electrons during chemical combinations VII. Oxidation Numbers • Stands for The # of electrons an atom gains, loses, or shares to become stable – (also is its ion’s charge) “ + ” # means lose that # of electrons “ - ” # means will gain/share that # of electrons VII. Oxidation Numbers • Ex. Sodium Chlorine +1 Na -1 Cl VIII. Writing Chemical Formulas • Use oxidation numbers • Use Criss-Cross Method • When writing formulas, remember compounds are Neutral • ***Positive Oxidation number written first (metal) VIII. Writing Chemical Formulas • Compound of Sulfur and Calcium? Writing Chemical Formulas • Compound of Sodium and Oxygen? Writing Chemical Formulas • Compound w/ Lithium and Carbonate ion CO3-2 Use Criss-Cross Method to write chemical formula: Answers: • 1. Mg and O • MgO • 2. O and Al • Al2O3 • 3. I and K • KI • 4. Mg and OH -1 • Mg(OH)2 • 5. Ca and CO3 -2 • CaCO3 VIII. Type of Bonds • A. Ionic Bonding: – Electrons are transferred – 1 atom loses and other atom gains electrons – Ion – charged atom, no longer neutral • Can be positive (+) or negative (-) • Na combining with Chlorine • The sum of the charges on the ions is zero!! Lithium Fluoride Ionic Bonds occur: • Between Metals bonding with Nonmetals • Nonmetal Sumo wrestler • Metal Child Ionic Compounds • Two ions have opposite electrical charges therefore attracted to each other – Holds Ionic Bonds together • Weak bond between elements • Ionic compounds form Crystal Lattice structure – regular repeating arrangement due to “+” tend to be near “-“ Ionic Bond • weaker bonds between elements than covalent bonds – Are easier to break into ions • But strong bonds b/w molecules – Substances tend to be solids at Room Temp – Have high melting points B. Covalent Bonding • “Co” – to share • “Valance” – electrons • electrons are shared, not transferred Covalent Bonding • Happens when both atoms attract electrons • Nonmetal with Nonmetal • Also Hydrogen with Nonmetal Covalent Bonding • Attraction b/w nucleus and shared electrons hold the atom together Covalent Bonding • Ex. Hydrogen with Carbon Covalent Bonding • - Covalent bonds often occur b/w atoms of same element Diatomic molecules Ex. O2, F2, Br2, I2, N2, H2 - When these are found in nature, always 2 atoms covalently bonded Covalent Bonding • F2 • Cl2 Covalent Bonding • More than 2 electrons can be shared b/w atoms Ex. Carbon and Oxygen Covalent Bonding • If 3 pairs of electrons are shared called a triple bond Ex. N2 Covalent Bonds • Strong bonds between elements • But Weak bonds b/w molecules – Triple bonds are strongest, then double, then single • Substances Tend to be liquids or gases at room temp. • Have Low boiling points Covalent Bonding • Molecule - smallest part of a bonded substance, compound, that has properties of that substance - Are neutral, no overall charge - Can be Polar or Nonpolar 1. Polar Covalent molecules • one end is slightly negative and one end is slightly positive, the overall molecule is still neutral • Ex. Water 2. Nonpolar Molecules • – Electrons are shared equally – Ex. Oil, fuels, fats IX. Polyatomic Ions • Group of covalently bonded atoms that act as a single atom when bonding with other atoms • As a group have a charge • Form ionic bonds with other elements Ex. Sodium and Hydroxide Ion • Calcium and Carbonate Ion X. Predicting Types of Bonds • Compound b/w Metal & Nonmetal – Form Ionic Bond • Compound b/w Nonmetal & Nonmetals – Form Covalent Bond – Like a Tug of war b/w 2 sumo wrestlers • Compound b/w polyatomic ion & element – Form ionic bond Predicting Types of Bonds • Ex. F + Mg ? – Ionic • O + Cl ? – Covalent • Na + OH-1 ? – Ionic XI. Naming compounds • **Binary compounds – compounds containing only two elements • See Handout • A. Binary Ionic 1. Write Positively Charged ion first usually the METAL 2. Then add Name of Negative ion with end changed to “-ide” Usually the NONMETAL NaCl Li2O CaO • B. Naming Compounds with Transition Metals remember transition metals may have more than one Oxidation Number - form positive ions Ex. Copper Iron • 1. Write name of Transition Metal first 2. In Parenthesis ( ) write a Roman Numeral to indicate the ox # of the Transition metal in this compound 3. Write name of nonmetal and Change end to “-ide” Ex. Cu+1 and Cl Cu+2 and Cl • Write the name for the following: 1. PbO 2. TiCl4 3. HgCl4 Write the Chemical formula: 1. Tin (IV) Flouride 2. Lead (I) Sulfide 3. Cobalt (III) Chloride • C. Naming Binary Molecular (covalently bonded) Compounds 1. Write element that is Least Electronegative first a. Use your table for this • 2. On the most electronegative element give a prefix for # of atoms of that element in the compound Prefix mono di tri tetra penta hexa hepta octa # of atoms 4 6 8 1 2 3 5 7 • Name the following: 1. SO2 3. SF6 2. SiO2 • X. Molar Mass of a Compound A. Mole – the unit of measurement used to count numbers of atoms, molecules or formula units Abbreviated “mol” The number of things in one mole is 6.02 X 1023 - Avogadro’s number 1 mole = 6.02 X 1023 • B. Using this we can count the number of atoms in one mole of a substance Ex. 1 mole of Carbon is 6.02 X 1023 at atoms of Carbon sodium 1 mole of Na is 6.02 X 1023 atoms of • Molar Mass – the mass of one mole of a substance Ex. The mass of one Carbon-12 atom is exactly 12 amu The mass of one mole of C-12 is 12 grams • ** Molar mass is the mass in grams of the average atomic mass of the substance** ex. Molar mass of Iron? - 55.847 grams • Try these! Find the molar mass of each substance. 1. Oxygen 2. Uranium 3. Copper • C.Finding the molar Mass of a Compound: -find the molar mass of each element in the compound -multiple it times the number atoms of that element in the compound - the Sum of the molar masses = the Molecular Mass (or gram formula weight) of the compound ex. Ethanol – C2 H6 O • Try These: 1. Ca Cl2 2. C6H5Br 3. (NH4)3PO4 • Which Has the largest Mass? 3 Mol of Magnesium or 1 mol of sucrose or 10 mol of helium