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Compound Names and Formulas. Ch 5.2 and 5.3. Polyatomic Ions. “Poly” means many, and “Atomic” means atom, so… Polyatomic ions are ions made of two or more atoms Examples: Hydrogen Carbonate, HCO 3 - Hydroxide Ion, OH - Ammonium Ion, HN 4 +. Polyatomic Ions.
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Compound Names and Formulas Ch 5.2 and 5.3
Polyatomic Ions • “Poly” means many, and “Atomic” means atom, so… • Polyatomic ions are ions made of two or more atoms • Examples: • Hydrogen Carbonate, HCO3- • Hydroxide Ion, OH- • Ammonium Ion, HN4+
Polyatomic Ions • The charge applies to the whole polyatomic ion • Example: Nitrite Ion, NO2- • The negative charge applies to the oxygen and to the nitrogen
Naming Ionic Compounds • Ionic compounds formed between positive ions (cations) and negative ions (anions) • Naming anions (negative ions): • Keep the same beginning, and change the ending • Examples: • Fluorine, F Fluoride Ion, F- • Chlorine, Cl Chloride Ion, Cl- • Oxygen, O Oxide Ion, O-2 • Nitrogen, N Nitride Ion, N-3
Naming Ionic Compounds • Keep the cation (positive ion) the same, and change the anion (negative ion) to its altered state (seen on previous slide) • Examples: • NaF • Made from Na+ and F- • Cation, Sodium Na+ Keep the same • Anion, Fluorine F- Change to Fluoride • Write the cation first, always • Therefore, the name is sodium fluoride
So how do you name this? • FeO vs. Fe2O3 • Cannot just say iron oxide—have to be more specific • To specify, we look at the charge of the cation (positive ion/the metal/the first atom) • Transition metals can have different charges depending on what they are bonded to
Naming Ionic Compounds • FeO • Fe is a transition metal and the charge can vary • Therefore start with O and figure out its charge • Oxygen is group 16, therefore forms -2 charges • Therefore Fe must have +2 charges to balance out the oxygen • Write the charge of the cation (Iron, +2) in parentheses after the metal, Iron (II) • Name of FeO: Iron (II) Oxide
How do you name… • Fe2O3 • What is the charge of one oxygen ion? • -2 • There are three oxygen atoms, therefore oxygen has an overall charge of (-2)(3) = -6 • Therefore iron must contribute a +6 charge to balance out the oxygen • There are two iron atoms, so each atom must have a +3 charge because (2)(+3) = +6 • Since iron has a charge of +3, the name of Fe2O3 is iron (III) oxide
Writing formulas… • What is the chemical formula for aluminum fluoride? • Use Table 4 (Page 159)Charge of an aluminum ion is +3 • Use Table 5 (Page 160)Charge of a fluoride ion is -1 • Step 1: Write down ions beside each other, with the cation first • Al+3F-
Writing ionic formulas… • What is the chemical formula for aluminum fluoride? • Al+3F- • Trick! Cross the charges to get the amount of ions in each. • Becomes AlF3
Practice… • Write lithium oxide • Li+1 • O-2 • Write the cation first: Li+1 O-2 • Cross the charges • Therefore lithium oxide is Li2O
Practice • Write beryllium chloride • Be+2 • Cl-1 • Write cation first. • Cross the charges. • So beryllium chloride is BeCl2
Practice • Write titanium (III) nitride • Remember: (III) corresponds to charge • So Ti+3 • Nitride-3 • Write the cation first. • If you cross the charges, you get Ti3N3 which can be reduced to a ratio of 1:1 • So titanium (III) nitride is TiN
Challenge Practice • Write cobalt (III) hydroxide • Co+3 • Hydroxide ion, OH- • Write the anion first, then cross the charges! • Co(OH)3 • Remember to keep OH is parentheses since it is one polyatomic ion!