Covalent Bonding

We begin with the molecule Molecule– two or more atoms covalently bound together Diatomic molecule—two of the same atom bound together

Diatomic Molecules These atoms never exist alone They always come in pairs Examples: Br  Br 2 I  I 2 N  N 2 Cl  Cl 2 H  H 2 O  O 2 F  F 2

Covalent Compounds Two nonmetals share electrons so both have 8 valence electrons. Exception: H Neither takes on a charge - no valence. Do not crisscross to determine formula. Must use prefixes in the name. Name tells you the formula. Example: N 2 O 4 is dinitrogen tetroxide. You cannot reduce the formulas!!!

Covalent Prefixes Mon – 1 Di – 2 Tri – 3 Tetra – 4 Penta – 5 Hexa – 6 Hepta – 7 Octa – 8 Nona – 9 Deca – 10 A prefix tells you the number of atoms of that element in the compound

Rules for Writing Covalent Compounds 1.Find the 1 st anion (nonmetal) and write down symbol 2.Look at the prefix and write it as a subscript after the symbol 3.Find the 2 nd anion (nonmetal) and write down symbol 4.Look at the prefix and write it as a subscript after the symbol *NO CHARGES *NO REDUCING *If there is no prefix, then it only a 1  don’t write 1’s

Examples: Write the Covalent Compound Phosphorus trichloride Nitrogen trihydride Dinitrogen hexafluoride Carbon tetrabromide PCl 3 NH 3 N 2 F 6 CBr 4

Rules for Naming Covalent Compounds 1. Name the prefix for # of atoms in the 1 st element -If the prefix is mono, drop it 2. Write the name for the 1 st element 3. Name the prefix for the # of atoms in the 2 nd element 4. Take the root name of the 2 nd element and add “ide”

Examples: Name the Covalent Compound N 2 O 3 CH 4 PO 5 S 2 F 3 Dinitrogen trioxide Carbon tetrahydide Phosphorus pentoxide disulfur trifluoride

Hydrates Compounds that trap water crystals when they form Both the name and the formula need to indicate how many water molecules are trapped In the name we add the word hydrate with a prefix to express the number of water molecules A dot is used in the formula to indicate “with” Examples Calcium chloride dihydrate is CaCl 2 ∙ 2H 2 O Chromium (III) nitrate hexahydrate is Cr(NO 3 ) 3 ∙ 6H 2 O

Acids Acids are compounds that contain one or more hydrogen atoms and produces H + (hydrogen ions) when dissolved in water The acid will consist of an anion combined with as many hydrogen ions as are needed to make the molecule electrically neutral. If the formula has hydrogen written first, then it usually indicates that the hydrogen is an H + cation and the compound is an acid.

Naming Acids Three Rules to Naming Acids 1.When the name of the anion ends in –ide, the acid name begins with the prefix hydro-. The stem on the anion has the suffix –ic and is followed by the word acid Example: HCl(aq) is hydrochloric acid H 2 S(aq) is hydrosulfuris acid

Naming Acids 2. When the anion name ends in –ite, the acid name is the stem of the anion with the suffix –ous, followed by the word acid Example: H 2 SO 3 is sulfurous acid (SO 3 is sulfite)

Naming Acids 3. When the anion name ends in –ate, and the acid name is the stem of the anion with the suffix –ic followed by the word acid Example: HNO 3 (aq) is nitric acid ((NO 3 ) us nitrate )

Writing Formulas for Acids Use the rules for writing the names of the acids in reverse Example: Hydrobromic acid Rule #1 hydro- prefix and -ic suffix gives us a combination of the hydrogen ion ( H + ) and the bromide ion or HBr Example: Phosphorous acid Refer to Rule #2, since we see the suffix –ous we know that is had to be an anion ending in –ite so we can look up phosphite (PO 3 3- ) and we need 3 H + to neutralize so H 3 PO 3

Writing Acids Continued… Example: Acetic acid Since we see the –ic suffix we will refer to rule #3 that tells us that the anion had to end in –ate so we look up the acetate ion (C 2 H 3 O 2 - ) and one hydrogen ion needed to neutralize which gives us HC 2 H 3 O 2.

More examples: H 2 SO 3 H 2 CO 3 HF Nitrous acid Perchloric acid Iodic acid Sulfurous acid Carbonic acid Hydrofluoric acid HNO 2 HClO 4 HIO 3

Naming Compounds Flow Chart Does the compound have a metal Yes No IONIC COVALENT (Metal cation + Nonmetal anion) (Two Nonmetals) Place metal first followed by nonmetal ending in –ide Place the nonmetal furthest Contain a Transition Metal? to the left on the periodic Yes No table first, then the other non- metal ending in –ide. Use Roman Do not use Numeral to tell Roman Numeral Use prefixes to tell the number of the valence of the Example atoms in the compound metal aluminum fluoride mono, di, tri, tetra, pent, hex Example Example iron(II)oxide dinitrogen trioxide

Mixed Examples KClO 2 CO 2 H 2 SO 4 NH 4 Br CuCO 3 Fe 2 O 3 HClO Potassium chlorite Carbon dioxide Sulfuric acid Ammonium bromide Copper (II) carbonate Iron (III) oxide Hypochlorous acid

More Mixed Examples Carbon tetrachloride Phosphorous pentachloride Aluminum oxide Copper (II) nitrate Chlorous acid Hydrophosphoric acid Iron (III) hydroxide CCl 4 PCl 5 Al 2 O 3 Cu(NO 3 ) 2 HClO 2 H 3 P Fe(OH) 3