Ionic Compounds – Polyatomic Ions (Metal + Polyatomic Ion)

Ionic Compounds – Polyatomic Ions

(Metal + Polyatomic Ion)

Learning Goals

1. To be able to determine ionic compounds containing polyatomic ions

2. To write chemical formulae containing polyatomic ions

3. To write chemical names containing polyatomic ions

Types of Compounds

Binary Compounds

(Metal + Non-metal)

Polyatomic Compounds

(Metal + Polyatomic ion)

Polyatomic Ions• Polyatomic ion: are ions that consists of a stable

group of several atoms acting together as a single charged particle.

• The ionic charge of a polyatomic ion is shared over the entire ion rather than being on just one atom.

• Polyatomic ions are sometimes called radicals. • These polyatomic ions bond with a metal to form

another type of ionic compound.• 3- Phosphate Ion

Formulas and Charges of Common Polyatomic Ions

Polyatomic Compound Name Ion Formula Ion Charge/Valence

carbonate CO3 2- 2-

nitrate NO3 - 1-

nitrite NO2 - 1-

phosphate PO4 3- 3-

sulphate SO4 2- 2-

sulphite SO3 2- 2-

hydroxide OH - 1-

chlorate ClO3 - 1-

*You must know how to use the back of your PT.

Writing Formulas

• Writing the formula for a polyatomic compound is similar to writing the formula for a binary ionic compound.

• First determine if it is a polyatomic compound? In other words, does it contain a _______metal_________ and a __polyatomic ion__ (a group of non-metals that act as one).

• Most polyatomic ions do NOT end in ____”-ide”____ except __hydroxide___.

• This is one of your clues to indicate that a compound contains a polyatomic ion.

What is the most common ending for the name of ....a polyatomic anion? “ –ate” (nitrate, chlorate, sulfate, phosphate)Or “ –ite” (nitrite, chlorite, sulfite, phosphite)

• Once you have determined that a compound is polyatomic then you can figure out the formula.

Let’s try!

Writing Formulas for Compounds Containing Polyatomic Ions

Method # 1

• Use the sum zero rule we learned

• Together on board!

Writing Formulas for Compounds Containing Polyatomic Ions

Method #2What is the chemical formula of copper (I) sulphate?Step 1: Write the symbol of each ion, with its charge. Cu1+ (SO4)-2

Step 2: Crisscross the numbers of the ionic charges so that they become subscripts.

Cu1+ (SO4)-2

Step 3: Write any necessary subscripts after the brackets around each ion.

The formula of copper (II) nitrate is Cu2(SO4)

WRITING NAMES

• When naming a polyatomic compound, the _____metal name_______ is first then the

___polyatomic ion name___.

Don’t forget about ___multivalent____ metals as some of them have multiple charges.

Let’s try!

Naming Compounds involving Polyatomic Ions

Write the name of the compound Fe(NO3)3 Step 1: Write the name of the metal and check

whether it has more than one possible ionic charge. Iron has two possible charges (+2 and +3)

Step 2: Determine the ionic charge of the metal.Fe(NO3)3

x + 3(-1) = 0 x = + 3Step 3: Write the name of the compound with the

Roman numeral if necessary.The name of Fe(NO3)3 is iron (III) nitrate.

Nitrites are not all bad news ...• Research suggests that sodium

nitrite may help protect heart tissue after a heart attack or heart transplant

• Nitrites and nitrates occur naturally in soil and are important plant nutrients

Hotdogs contain many chemical additives

Sodium nitritePreservative and colour enhancer

Sodium phosphateBinding agent

Sodium erythrobatePreservative