Writing Formulas & Names For Polyatomic Compounds printable pdf download

Nomenclature & Formula Writing 4

Writing Formulas & Names for Polyatomic Compounds

INFORMATION

Polyatomic ions, as their name suggests, are ions containing more than one atom.

Unlike the atoms combined in binary ionic compounds, the atoms in polyatomic ions are molecules –

atoms joined by covalent bonds. The nature and properties of covalent bonds are discussed in a later

activity, but for now it is important to know that the atoms in

The atoms in a polyatomic

the polyatomic ion collectively behave like an ion for the

purpose of forming ionic compounds.

ion collectively behave

like an ion for the purpose

The charges of polyatomic compounds are fixed, a result of the

of forming ionic bonds.

nature of the bonds between the atoms in them and the number

of electrons in those bonds. Valences for polyatomic ions are

not determined by patterns, like with representative elements. Each polyatomic ion has a fixed charge

based on its structure (structure indicated the connections between atoms and the molecule’s

configuration in space – the structure of molecules will also be investigated at a later time). These

charges are determined by looking up the ion on a table of polyatomic ions, or by memorizing the ions

and their charges.

Polyatomic ions are just that – ions – and therefore always have a charge associated with them.

Whenever a polyatomic ion is written as a chemical formula (as opposed to part of a compound), the

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charge must accompany it. For example, the polyatomic anion nitrate is written as NO

In later activities, the charge of polyatomic ions will be determined by the application valence bonding

theory – the governing principles that drive valence bonding. For now, the charges of polyatomic ions

will be provided in the reference table mentioned above.

Understanding Oxyanions

Oxyanions are polyatomic anions containing one or more oxygen atoms, but no hydrogen atoms. Many

oxyanions have the special property that the root element remains the same as the number of oxygen

atoms changes, but the charge stays the same.

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Hypochlorite (ClO

), chlorite (ClO

), chlorate (ClO

), and perchlorate (ClO

) are all related

(they have a chlorine root), and even though they have different numbers of oxygen atoms, they all

have a charge of -1.

The suffix -ite indicates one fewer oxygen than a compound ending in -ate. The prefix hypo- indicates

one less than -ite, and the prefix per- indicates one more than -ate.

The increasing order for the prefixes is hypo-, -ite, -ate, per-.

Writing Formulas & Names for Polyatomic Ionic Compounds / 1

Writing Formulas & Names For Polyatomic Compounds