Unit 6B: Naming and Writing Formulas for Ionic and Covalent Compounds

Polyatomic Ions

Polyatomic ions are groups of atoms that are covalently bonded and have a charge.• PO4

3- = phosphate ion

• SO42- = sulfate ion

Polyatomic Ions

Ending of –ate or –ite means there are oxygen atoms in the formula of the ion. • SO4

2- = sulfate

• SO32- = sulfite

Polyatomic Ions

The –ate ending always has one more oxygen than the –ite ending.

SO42- = sulfate NO3

- = nitrate

SO32- = sulfite NO2

- = nitrite

Names for Cations and Anions

Monatomic Cation Names: Same as element name• Na+ sodium ion• Al3+ aluminum ion

Names for Cations and Anions

What about transition metals with more than one charge? • Fe2+ iron(II)• Fe3+ iron(III)

Names for Cations and Anions

What about transition metals with more than one charge?• Cu+ copper(I)• Cu2+ copper(II)

Names for Cations and Anions

Monatomic Anion Names: Element name with –ide ending• S2- sulfide ion• O2- oxide ion

Names for Cations and Anions

Monatomic Anion Names: Element name with –ide ending• P3- phosphide ion• N3- nitride ion

Naming Binary Ionic Compounds

A binary compound is composed of two elements and can be ionic or molecular (covalent).• Binary ionic compound = metal, then

nonmetal

Naming Binary Ionic Compounds

NaCl • sodium chlorideCa3P2 • calcium phosphide

CuCl2 • copper(II) chlorideNi3N2 • nickel(II) nitride

Naming Compounds with Polyatomic Ions

To name an ionic compound with a polyatomic ion, write the name of the cation first, followed by the name of the anion.

Naming Compounds with Polyatomic Ions

NaNO3 • sodium nitrate(NH4)2SO4 • ammonium sulfate

Ca(NO3)2 • calcium nitrate

Writing Formulas for Ionic Compounds

The metal (cation) always goes first, followed by the nonmetal (anion).

Writing Formulas for Ionic Compounds

Use the “criss-cross method” to balance out the charges.

Writing Formulas for Ionic Compounds

Use the “criss-cross method” to balance out the charges.

Parenthesis must be used if more than one polyatomic ion is needed.

Writing Formulas for Ionic Compounds

Use the “criss-cross method” to balance out the charges.

Always reduce the subscripts to lowest terms

Naming Binary Molecular Compounds

We use prefixes to tell how many of each element are in a binary molecular compound.

Naming Binary Molecular Compounds

Name the elements in the order listed in the compound, using prefixes to indicate the number of each element.• Never use the prefix mono- for the first

element• The second element always ends in -ide

Naming Binary Molecular Compounds

CO• carbon monoxideCO2

• carbon dioxide

P4O10

• tetraphosphorus decoxide

N2O5

• dinitrogen pentoxide

Writing Formulas forBinary Molecular Compounds

Write the formula in the same order the elements are named.

The prefix tells you the subscript for each element.

Writing Formulas forBinary Molecular Compounds

Dioxygen monofluoride • O2F

Phosphorus trichloride• PCl3

Review

Binary Ionic Compounds Binary Molecular Compounds

Electrons Give and Take Shared

Type of Elements Metal + Nonmetal Nonmetal + Nonmetal

Naming NO prefixes YES prefixes

YES Roman numerals (if > 1 charge) NO Roman numerals

Review