The Polyatomic Ion Problem!

Knowing dot structures (Using only the Octet Rule) of polyatomic ions (Corwin Chapter 12 section 12.5), and some keen observations you can boil it down to six questions to determine the formula and the charge on a polyatomic ion :

1. What is the formula for the –ate polyatomic ion?

See Taylor’s 3/4 Rule:

http://www.fccj.us/PolyatomicIons/Taylor34OxygenRuleHandout.htm

What is the charge on –ate polyatomic ion?

See Taylor’s Charge Rule:

http://www.fccj.us/PolyatomicIons/TaylorChargeRuleHandout.htm

2. What happens to the charge on the polyatomic ion when you attach hydrogen atom(s) to the polyatomic 2- and 3- anions?

The hydrogen fills one of the electron holes on the polyatomic ion and it results in an increase of +1 to the 2- charge ( making the charge1-) or 3- charge (making the charge 2-)

Carbonate is CO₃^{2- so} hydrogen carbonate or bicarbonate is HCO₃^1-

Phosphate is PO₄^3- so hydrogen phosphate is HPO₄^2-

3. What does –ite mean in a polyatomic ion?

One less oxygen than the –ate ion, but with the same charge as the –ate ion.

Nitrate is NO₃^1- , but Nitrite is NO₂^1-

5. How do the hypo- and per- prefixes apply to polyatomic ions?

Hypo- means one oxygen less than –ite but the same charge as –ite

Chlorite is ClO₂^{1- so} hypochlorite is ClO^1-

Per- means one oxygen more than –ate but the same charge as –ate

Chlorate is ClO₃^{1- so} Perchlorate is ClO₄^1-

6. What are the two –ide polyatomic negative charged Anions and the two -ium positive charged polyatomic Cations?

Hydroxide is OH^1- Ammonium is NH₄¹⁺

Cyanide is CN^1- Hydronium is H₃O¹⁺