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Bonding for OCR GCSE Chemistry

Bonding

This page covers the following topics:

1. Ionic bonding
2. Covalent bonding

Ionic bonds form between cations (positive ions) and anions (negative ions). Many ionic compounds (salts) are formed by metals and non-metals. When an ionic bond is formed by a metal (usually from groups 1, 2) and a non-metal (usually from groups 6, 7), electrons are transferred from the metal atoms to the non-metal atoms to form metal cations and non-metal anions. The electrostatic attraction between these ions creates an ionic bond, which can be depicted using a dot-and-cross diagram.

Ionic bonding

Covalent bonds arise from the sharing of pairs of electrons between two non-metal atoms. Covalent bonds are stronger than ionic or metallic bonds. Most molecules have covalent bonds. Hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine exist naturally as diatomic molecules Hโ‚‚, Nโ‚‚, Oโ‚‚, Fโ‚‚, Clโ‚‚, Brโ‚‚, Iโ‚‚. For these diatomic molecules, the number of shared electron pairs in a molecule is the same as the number of unpaired electrons in a single atom. A single bond is formed when 2, a double when 4 and a triple when 6 electrons are shared.

Covalent bonding

1

Draw a dot-and-cross diagram to represent an ionic bond in KBr.

When an ionic bond is formed by a metal (usually from groups 1, 2) and a non-metal (usually from groups 6, 7), electrons are transferred from the metal atoms to the non-metal atoms to form metal cations and metal anions. The electrostatic attraction between these ions creates an ionic bond, which can be depicted using a dot-and-cross diagram.

Potassium is in group 1 and it has 1 valence electron. Bromine is in group 7 and has 7 valence electrons. Thus, bromide ion has 7 dots and 1 cross (the electron from potassium).

image

Draw a dot-and-cross diagram to represent an ionic bond in KBr.

2

Which two groups of the periodic table are most cations in ionic compounds from?

Cations (positive ions) are frequently formed by metals from groups 1 and 2.

1, 2

Which two groups of the periodic table are most cations in ionic compounds from?

3

Explain what holds ions in an ionic compound together.

When an ionic bond is formed between cations and anions, the electrostatic attraction between these ions creates an ionic bond that holds the ions together.

electrostatic attraction between ions

Explain what holds ions in an ionic compound together.

4

Which of the following are the most likely to form a covalent bond?

A) A metal and a non-metal
B) A metal and a metal
C) A non-metal and a non-metal

Covalent bonds arise from the sharing of a pairs of electrons between two non-metal atoms.

C

Which of the following are the most likely to form a covalent bond? 

A) A metal and a non-metal 
B) A metal and a metal 
C) A non-metal and a non-metal

5

Compare a cation with an anion.

Both a cation and an anion are ions, that is, charged particles. A cation is positively charged while an anion is negatively charged.

Both are ions, cation - positive, anion - negative.

Compare a cation with an anion.

End of page

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