L1: Ionic Compounds

Objectives

Determine the formula of an ionic compound from the charges on the ions present
Use the symbols of the elements and write the formulae of simple compounds

Simple Ions

Group 1 (Alkali Metals) have 1 electron in their outer shell. It is easy for them to lose this electron to become a 1+ cation.

Group 2 (Alkaline Earth Metals) have 2 electrons in their outer shell. It is easy for them to lose these electrons to become a 2+ cation

Group 7 (Halogens) have 7 electrons in their outer shell. It is easy for them to gain one electron to become a 1- anion.

Group 6 (Chalcogens) have 6 electrons in their outer shell. It is easy for them to gain two electrons to become a 2- anion.

Polyatomic (complex) ions

These are made of several atoms bonded together. You need to memorise the names and formulae of these polyatomic ions

Carbonate ion, CO₃^2-

Sulfate ion, SO₄^2-

Ammonium ion, NH₄⁺

Hydroxide ion, OH^-

Nitrate ion, NO₃^-

Transition metal ions

Many (but not all) transition metals can form cations with different charges. For example, iron can produce cations with a charge of +2 or +3. Copper can produce cations with a charge of +1, +2, or +3.

If the metal in an ionic compound can form different cations, we identify the cation present by including its charge using Roman numerals in brackets

E.g. iron (III) chloride = made of Fe³⁺ and Cl^-

iron (II) oxide = made of Fe²⁺ and O^2-

C4 Stoichiometry L1: Ionic Compounds and Balancing Equations

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