ph_ch003

ph_ch003 - Chapter 03 Molecules Compounds and Chemical...

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1 Chapter 03 Molecules, Compounds, and Chemical Equations Elements and Compounds Elements – cannot be broken down further Elements Some elements exist as diatomic molecules. H 2 O 2 N 2 F 2 Cl 2 Br 2 and I 2 Other elements occur as polyatomic molecules P 4 S 8 Se 8
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2 Elements Compounds Compounds are held together by chemical bonds. There are two types of chemical bonds – Ionic Bonds-attraction between oppositely charged ions. Molecules are not formed. (crystal lattice) – Covalent Bonds-sharing of electrons between the two valence shells. Molecules are formed In both cases the driving force is the noble gas configuration – we will talk about this later Ionic vs. Molecular Compounds Propane – contains individual C 3 H 8 molecules Table salt – contains an array of Na + ions and Cl - ions
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3 Formula Empirical Formula • for molecular compounds it is the smallest whole number ratio of elements making up the molecule. • for ionic compounds it is just the ratio of the elements making up the compound. Molecular Formula • Number of atoms of each element making up the molecules (only for molecular compounds) Chemical Formulas Hydrogen Peroxide Molecular Formula = H 2 O 2 Empirical Formula = HO Benzene Molecular Formula = C 6 H 6 Empirical Formula = CH Glucose Molecular Formula = C 6 H 12 O 6 Empirical Formula = CH 2 O Tro, Chemistry: A Molecular Approach 11 Molecular View of Elements and Compounds Ionic Compounds – how and why metals Nonmetals Ionic compounds are formed between a metal and a non metal. We can predict the likely chemical formula for the ionic compound by the position of the element in the periodic chart
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4 Ionic Compounds – how and why Group IA - +1 Group IIA +2 Group IIIA +3 Group IV A (usually covalent) Group VIIA -1 Group VIA -2 Group VA -3 Group VIIIA do not react Ionic Compounds The metal is positively charged and it is called the cation The nonmetal is negatively charged and it is called the anion We may also have polyatomic ions. Ionic Compounds The total charge on a compound must be zero. The charge on the cation and the anion must add up to zero. Charges must be balanced. Verify that the charges are balanced: NaCl Na 2 O Na 3 N Al 2 O3 MgCl 2 MgS Mg 3 N 2 Writing Formulas for Ionic Compounds 1. Write the symbol for the metal cation and its charge 2. Write the symbol for the nonmetal anion and its charge 3. Charge (without sign) becomes subscript for other ion 4. Reduce subscripts to smallest whole number ratio 5. Check that the sum of the charges of the cation cancels the sum of the anions
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5 Write the formula of a compound made from aluminum ions and oxide ions 1. Write the symbol for the metal cation and its charge 2. Write the symbol for the nonmetal anion and its charge 3. Charge (without sign) becomes subscript for other ion 4. Reduce subscripts to smallest whole number ratio 5. Check that the total charge of the cations cancels the total charge of the anions Al +3 column 3A O 2- column 6A Al +3 O 2- Al 2 O 3 Al = (2)·(+3) = +6
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This note was uploaded on 02/17/2011 for the course CHM 1045 taught by Professor Jeffreyjoens during the Spring '08 term at FIU.

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ph_ch003 - Chapter 03 Molecules Compounds and Chemical...

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