1. Chapter 7 Chemical formulas and Bonding Elements tend to react to fill out their outer electron shell (s and p orbitals). This results in a more stable electron configuration like the noble gases. Metal + Nonmetal –Transfer of electrons to form positive and negative ions. –The positive and negative ions come together (ionic bond). –Will form a salt or an oxide (if with oxygen) –Opposite ions attract to form a strong ionic bond. –Salts and oxides have high melting points. –A salt crystal is alternating array of + and – ions –Electrolytes conduct electricity when placed in water

2. Nonmetal + Nonmetal –more equal competition for electrons –Atoms end up sharing electrons –Molecules are formed –Atoms are held together by mutual attraction for shared electrons (covalent bond) –Most molecules do not form ions in water. (non- electrolytes) –Lower melting and boiling points than salts. To melt an ionic compound must break ionic bonds To melt molecular compounds only have to overcome attractive forces between molecules (these tend to be weak)

3. A closer look at bonding The difference in electronegativity between atoms will determine the degree of ionic character their bond will have. 0.42.1 Non-polar Polar covalent bond ionic Non-polar Polar covalent bond ionic Covalent bond Covalent bond sharingunequal sharing transfer

4. Lewis structures (electron-dot structures) A way to show only outer (valence) electrons

5. Most useful to show bonding For metal + nonmetal you must show charge on ions Na + Cl NaCl Na + Cl NaCl 2K + O K 2 O 2K + O K 2 O

6. For nonmetal + nonmetal the shared electrons are in between the atom symbols Single bond – one pair of shared electrons Double bond- two pairs of shared electrons Triple bond – three pairs of shared electrons

7. Polyatomic ion – an ion composed of two or more atoms Ammonium ion NH 4 +1 Hydroxide ion OH -1 Sulfate ion SO 4 -2 Nitrate ion NO 3 -1 Phosphate ion PO 4 -3 Carbonate ion CO 3 -2

8. Crisscross method of determining a formula of an ionic compound 1. Write the symbols with the positive element first. 2. Place the oxidation number of the elements above the symbols. 3. Crisscross them for combining ratios 4. Reduce the lowest terms if possible Na + O Na +1 O -2 Na 2 O Al + OAl +3 O -2 Al 2 O 3 S + CaCa +2 S +2 CaS

9. Naming Compounds – IUPAC method (International Union of Pure and Applied Chemistry) Case 1 – Metal with only one oxidation number Give the name of the metal and then the name of the nonmetal with an ide ending NaCl Al 2 O 3 sodium chloride aluminum oxide Na 2 S Na 2 S sodium sulfide

10. Case 2 – A metal with more than one possible oxidation number and a nonmetal Give the name of the metal and use a Roman numeral to designate its oxidation number. CrOFe 2 O 3 Chromium II oxide Iron III oxide

11. Case 3 – a compound that contains a polyatomic ion. Use the name of the polyatomic ion (look this up) to name the compound. Li 2 SO 4 NH 4 OH lithium sulfateamonium hydroxide

12. Case 4 – A compound composed of two nonmetals Use a prefix to designate the number of each element in the molecule. (see page 246 for prefixes) CCl 4 CO 2 CCl 4 CO 2 carbon tetrachloride carbon dioxide CO carbon monoxide

13. Types of Chemical Formulas Example - hexane Molecular formula – gives the number of each type of atom in the compound. Example: C 6 H 14 Empirical formula – gives the lowest ratio of each type of atom in the compound. Example C 3 H 7 Structural formula – gives a good idea of the arrangement of atoms in the molecule. Example: CH 3 CH 2 CH 2 CH 2 CH 2 CH 3