Chem-To-Go Lesson 15Unit 4

IONIC BONDING –

ROMAN NUMERALS

Need a periodic table and an ion sheet

WHAT IS THE PURPOSE OF ROMAN NUMERALS?

The transition metals and Group 4A have unpredictable cation charges.

The Roman numeral communicates to the reader which form of the ion was used to create the compound. Example 1:

You say, “Copper (I) oxide.” I know to write: Cu2O

Example 2: You say, “Copper (II) oxide.” I know to write: CuO

The Roman numeral makes a diff erence in the chemical formula.

Example 1: Copper (I) oxide

Example 2: Copper (II) oxide

1. When you are given a name and asked for a formula, Roman numerals are simple.

2. The Roman numeral will be given, and you’ll need to use it as you criss cross to write the formula.

Example 1: Name given in problem:

Nickel (II) nitrite You criss-cross using Ni+2

Example 2: Name given in problem:

Lead(II) acetate You criss-cross using Pb+2

WHEN WRITING FORMULAS = SIMPLE

Example 1: Nickel(II) nitrite

Example 2: Lead(II) acetate

o When you are given a formula and asked for a name, then you cannot take short-cuts.

o The Roman numerals is not always obvious.1. Identify the charge of the

negative ion. They are ALWAYS predictable.

2. Calculate the overall negative charge of the compound.

• (Anion Subscript)(Negative Charge)

3. The metal ion must cancel the overall negative charge.

4. Calculate the metal charge by dividing the overall negative charge by the subscript of the metal.

WHEN WRITING NAMES = COMPLICATED

Example : Sn(SO4)2

o Charge of the anion:

o Overall negative charge:(Anion subscript)(Negative charge)

o Subscript of metal:

o Roman numeral calculation:

WHEN WRITING NAMES = COMPLICATED

Example : TiS

o Charge of the anion:

o Overall negative charge:(Anion subscript)(Negative charge)

o Subscript of metal:

o Roman numeral calculation:

Example : Cu3PO4

o Charge of the anion:

o Overall negative charge:(Anion subscript)(Negative charge)

o Subscript of metal:

o Roman numeral calculation: