Ionic Compounds: - are made up of positive and negative ions arranged in a crystal structure. Covalent Molecules: - are made up of atoms sharing electrons.

Salt, NaCl

4.2 – Ionic and Covalent Compound Naming

Water, H2O

Naming Ionic Compounds:

– name of an ionic compound = cation anion-ide

– Ex.1: magnesium and oxygen

cation anion-ide

Magnesium ox + ide

Magnesium oxide

– Ex.2: what is the name of Ca3N2?

Ca = calcium; N = nitrogen

Drop the end of the anion and add –ide

Calcium nitride

– Ex.3: What is the name of BaCl2?

Barium chloride

Magnesium oxide is used as a drying agent.

Writing formulas for Ionic Compounds Remember: positive charges must = negative charges

Ex.1: What is the formula for magnesium phosphide?

Magnesium is Mg2+ Phosphorous is P3–

Lowest common multiple of 2 and 3 is 6

3 Mg2+ ions & 2 P3– ions (6 +ve’s & 6 –ve’s)

Magnesium phosphide = Mg3P2

Ex.2: What is the formula for calcium oxide? Calcium is Ca2+ Oxygen is O2–

1 Ca2+ ion & 1 O2– ion Calcium oxide = CaO

Drawing Formula Diagrams

Examples on overhead:

– Lithium nitride

– Barium sulphide

Ionic Compound with a Multivalent Metal

Multivalent: some transition elements have more than one charge. – Roman numerals are used after the metal

name to indicate which ion was used

Ex. 1 What is the formula manganese(III) sulphide?

This manganese is Mn3+ Sulphur is S2–

Lowest common multiple of 3 and 2 is 6

2 Mn3+ ions and 3 S2– ions

Mn2S3

You try!

What is the name for TiF4?

Titanium can be Ti4+ or Ti3+ Fluorine is F–

From the ratio in the formula you can find out it is Ti4+

1 Ti4+ ion and 4 F– ions

Titanium (IV) fluoride

Polyatomic Ions

are made up of several atoms joined together by covalent bonds

– The whole group has a + or – charge, not individual atoms.

Ex.1 What is the formula of sodium sulphate?

Na+ and SO42–

Na2SO4

Ex.2: What is the name of the compound KClO?

K+ = potassium ClO– = hypochlorite

Potassium hypochlorite

Ex.3: What is the formula for Calcium nitrate?

Ca2+ and NO3-

Ca(NO3)2

* Note the brackets around NO3 show there are two of the nitrate ions present

Naming Simple Covalent Compounds Prefixes are used before the atom name to

indicate the number of atoms in the molecule.

Examples: CO = carbon monoxide

CO2 = carbon dioxide Write the most metallic atom (furthest left) first, then add -ide to the end of the second atom’s name

Examples:

What is the name of the molecule Si3P6?

– Trisilicon hexaphosphide

What is the chemical formula for the molecule trinitrogen tetrachloride?

– N3Cl4

How do you know which type it is?

To determine whether a compound is ionic or covalent:

- Examine the formula

• Ionic compounds start with a metal or the ammonium ion

• Covalent compounds start with a non-metal

Take the Section 4.2 Quiz