Ionic compounds with 3 or more elements contain polyatomic ions. We’ll show you how to write the formulas for compounds with polyatomic ions.

A polyatomic ion is Polyatomic ion - A group of atoms that stay together and act as a single unit. The whole ion has a charge.

A group of atoms that bond together O N O O 3– Polyatomic ion - A group of atoms that stay together and act as a single unit. The whole ion has a charge.

And it stays together to act like a single unit O N O O 3– Polyatomic ion - A group of atoms that stays together and acts as a single unit. The whole ion has a charge.

The whole ion has a net charge. O N O – O Polyatomic ion - A group of atoms that stays together and acts as a single unit. The whole ion has a charge.

In the example shown here there is one nitrogen atom and three oxygen atoms and the ion has a charge of negative 1, so the formula is (click) NO3 minus O N O – O Polyatomic ion - A group of atoms that stays together and acts as a single unit. The whole ion has a charge. Formula: Name: nitrate

The name of this polyatomic ion (click) is nitrate. O N O – O Polyatomic ion - A group of atoms that stays together and acts as a single unit. The whole ion has a charge. Formula: Name: nitrate

Here is a table that contains the formulas and charges of the ions we will be using in this course. Formulas and Charges of Common Ions

The polyatomic ions are the ones with more than one element. In this table, they are shaded. The other ions on here are not polyatomic, they are ions of single elements. Formulas and Charges of Common Ions

polyatomic ions are easy to recognize because the formula always has more than one capital letter. Formulas and Charges of Common Ions More than one Capital Letter in the Formula

For example, the hydroxide ion is polyatomic, because it has a capital “O” and a capital “H”. You will always be able to use a table like this when you are writing formulas for ionic compounds. Formulas and Charges of Common Ions More than one Capital Letter in the Formula

The only positive polyatomic ion we’ll be using is ammonium, with the formula NH4 plus. Formulas and Charges of Common Ions Positive Polyatomic Ion

All the negative polyatomic ions are shaded in pink. You can see, there are quite a few of these. Formulas and Charges of Common Ions Negative Polyatomic Ions

If you look at the names of these, you can see that many of them end in “ate”, like acetate, carbonate, and nitrate Formulas and Charges of Common Ions End in “ate”

A few of the names end in “ite”, like chlorite, hypochlorite, and nitrite Formulas and Charges of Common Ions End in “ite”

And three polyatomic ions have names ending in “ide”, cyanide, bisulphide, and hydroxide. The other ions whose names in in “ide” on this table are not polyatomic ions, they are ions of a single element. Formulas and Charges of Common Ions End in “ide”

Notice that 4 of the polyatomic ions, have two possible names, separated by a comma. Either name can be used. For example HCO3 minus can be called hydrogen carbonate or bicarbonate. Formulas and Charges of Common Ions 2 possible names

CrO 3 – We’re asked to write the formula for barium chlorate Write the formula for barium chlorate Ba 2+ CrO 3 – +2 –2 Total Positive Charge Total Negative Charge

CrO 3 – Looking up barium on the periodic table Ba 2+ CrO 3 – +2 –2 Total Positive Charge Total Negative Charge Write the formula for barium chlorate

CrO 3 – We see that it forms the Ba 2 plus ion Ba 2+ CrO 3 – +2 –2 Total Positive Charge Total Negative Charge Write the formula for barium chlorate

ClO 3 – Chlorate is a polyatomic ion on the ion table. Ba 2+ CrO 3 – +2 –2 Total Positive Charge Total Negative Charge Write the formula for barium chlorate

ClO 3 – It’s formula is ClO3 with a negative 1 charge. Ba 2+ ClO 3 – +2 –2 Total Positive Charge Total Negative Charge Write the formula for barium chlorate

ClO 3 – With one barium and one chlorate ion, the total positive charge is positive 2 and the total negative charge is negative 1. Write the formula for barium chlorate Ba 2+ ClO 3 – +2 –1 Total Positive Charge Total Negative Charge

ClO 3 – The charges are not balanced, they do not add up to zero. Write the formula for barium chlorate Ba 2+ ClO 3 – +2 –1 Total Positive Charge Total Negative Charge These do not add up to zero

ClO 3 – So we add one more chlorate ion Write the formula for barium chlorate Ba 2+ ClO 3 – +2 –1 Total Positive Charge Total Negative Charge

ClO 3 – And the total negative charge is now negative 2 Write the formula for barium chlorate Ba 2+ ClO 3 – +2 –2 Total Positive Charge Total Negative Charge

ClO 3 – So now the charges are balanced. Write the formula for barium chlorate Ba 2+ ClO 3 – +2 –2 Total Positive Charge Total Negative Charge NOW these add up to zero

ClO 3 – There is one Ba ion Write the formula for barium chlorate Ba 2+ ClO 3 – Ba(ClO 3 ) 2

ClO 3 – To two chlorate ions. Write the formula for barium chlorate Ba 2+ ClO 3 – Ba(ClO 3 ) 2

ClO 3 – The subscript 2 here, to the right of ClO3, means there are 2 chlorate ions in the formula. Whenever a subscript refers to a polyatomic ion… Write the formula for barium chlorate Ba 2+ ClO 3 – Ba(ClO 3 ) 2 A subscript referring to a polyatomic ion

ClO 3 – Brackets must be drawn around the polyatomic ion. Write the formula for barium chlorate Ba 2+ ClO 3 – Ba(ClO 3 ) 2 A subscript referring to a polyatomic ion

ClO 3 – And now we have the final formula for barium chlorate: Ba, Write the formula for barium chlorate Ba 2+ ClO 3 – Ba(ClO 3 ) 2 Formula:

ClO 3 – ClO3 in brackets, Write the formula for barium chlorate Ba 2+ ClO 3 – Ba(ClO 3 ) 2 Formula:

ClO 3 – 2 Write the formula for barium chlorate Ba 2+ ClO 3 – Ba(ClO 3 ) 2 Formula:

ClO 3 – The formula tells us that the compound barium chlorate has one barium ion Write the formula for barium chlorate Ba 2+ ClO 3 – Ba(ClO 3 ) 2 Formula: 1 barium ion

ClO 3 – For every 2 chlorate ions Write the formula for barium chlorate Ba 2+ ClO 3 – Ba(ClO 3 ) 2 Formula: 1 barium ion2 chlorate ions