Structure and Bonding

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1.1 Chemical bonding

Elements react to form compounds by gainings or losing electrons, or by sharing electrons.

Atoms of metals in Group 1 combine with atoms of non-metals in Group 7 by transferring electrons to form ions that have electronic structures of noble gases.

1. It's made of two non-metals.

2. KBr, Na2O, MgO

3. Lithium atoms lose an electron to form a lithium ion that has a positive charge. Fluorine atoms gain an electron to form a fluorine ion that has a negative charge.

1.2 Ionic bonding

Ionic compounds are held together by strong forces between the oppositely charged ions.  This is called ionic bonding.

The ions form a giant structure or lattice.  The strong forces of attraction act throughout the lattice.

We can represent atoms and ions using dot and cross diagrams.

1. Sodium ions have a single positive charge and magnesium ions have a double positive charge.  Chloride ions have a single negative charge.

2. (http://www.bbc.co.uk/schools/gcsebitesize/science/images/diag_sodium_chloride.gif)

1.3 Formulae of ionic compounds

The charges on the ions in an ionic compound always cancel each other out.

The formula of an ionic compounds shows the ratio of ions present in the compound.

Sometimes we need brackets to show the ratio of ions in a compound, e.g. magnesium hydroxide, Mg(OH)2

1. CaFl2, Na2

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