Additional Science-Chem

Ions are electrically charged particles formed when atoms lose or gain electrons. They have the same electronic structures as noble gases. Metal atoms=positive ions non-metal atoms=negative ions The strong electrostatic forces of attraction between oppositely charged ions are called ionic bonds. How ions form Ions are electrically charged particles formed when atoms lose or gain electrons. This loss or gain leaves a complete highest energy level Metal atoms and non-metal atoms go in opposite directions when they ionise: Metal atoms lose the electron, or electrons, in their highest energy level and become positively charged ions Non-metal atoms gain an electron, or electrons, from another atom to become negatively charged ions

Ionic bonding

When metals react with non-metals, electrons are transferred from the metal atoms to the non-metal atoms, forming ions. The resulting compound is called an ionic compound.

Consider reactions between metals and non-metals, for example:

sodium + chlorine → sodium chloride

magnesium + oxygen → magnesium oxide

calcium + chlorine → calcium chloride

In each of these reactions, the metal atoms give electrons to the non-metal atoms. The metal atoms become positive ions and the non-metal atoms become negative ions.

There is a strong electrostatic force of attraction between these oppositely charged ions, called an ionic bond. The animation shows ionic bonds being formed in sodium chloride, magnesium oxide and calcium chloride

Formulae of ionic compounds

Ionic compounds are represented by formulae. Symbols and numbers show the atoms in the compound.

For example: ZnCO3 is the formula for zinc carbonate.

One zinc atom (Zn) and one carbon atom (C) are chemically bonded with three oxygen atoms (O3). Notice that we don't need to write a 1 next to the Zn or C.

Sometimes brackets are used.

For example: Fe(OH)3 is the formula for iron(III) hydroxide.

Iron(III) hydroxide consists of one iron atom joined with three oxygen and three hydrogen atoms. The formula is written like this because the oxygen and hydrogen atom often act together

The formula of a compound can be worked out if the ions in it are known. For example, the compound formed from Na+ and SO42- will consist of two Na+ ions to every one SO42- ion so that the compound is neutral overall. The formula is therefore Na2SO4.