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Covalent Bonding

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Normally, Covalent Bonds form between two non-metal atoms. Non-metals are found to the right of the Periodic Table and will have outer shells that are half-filled or more than half-filled.

They will tend to gain electrons by sharing electrons to become more stable.

The number of unpaired electrons will determine the number of bonds an atom can form.

Hydrogen has one single electron which it can - share to form a single covalent bond.

Hydrogen appears in a wide variety of molecules but can never form more than one single covalent bond.

Similarly, Chlorine appears in a wide variety of molecules but can never form more than one single covalent bond.

Oxygen has 6 electrons (2 pairs and 2 singles) and can form two single covalent bonds or one double covalent bond (maximum of 2 bonds).

Nitrogen has 5 electrons (1 pair and 3 singles) and can form three single covalent bonds or one triple covalent bond (maximum of 3 bonds).

Carbon with 4 single electrons is the most versatile and can form single, double and triple covalent bonds (maximum of 4 bonds).

Bonding Pictures

There are many ways of representing the formation of Covalent Bonds. One of the 'best' shows the orbitals overlapping to share electrons.

In exams, however, you are more likely to be asked to draw 'electron-dot' diagrams to represent shells overlapping to share electrons.

In particular, you would be expected to draw diagrams to show the electrons in molecules of methane (CH4), ammonia (NH3) and water (H2O).

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Molecular Shapes

Similarly, you would be expected to know the shapes of simple molecules like methane (CH4), ammonia (NH3) and water (H2O).

In methane (CH4), all 4 orbitals are used to form bonds and the molecule is the same tetrahedral shape as the orbitals have.

In ammonia (NH3) only 3 orbitals are used and the molecule is pyramidal in shape.

in water (H2O) only 2 orbitals are used and the molecule is bent (non-linear) in shape.

Quick Check 4

Question9.

The shapes of some molecules are shown below.

Phosphine is a compound of phosphorus and hydrogen. The shape of a molecule of phosphine is likely to be

tetrahedral pyramidal bent linear.

Question 10.

The shapes of some molecules are shown below.

'Bad egg gas' is a compound of hydrogen and sulfur. The shape of a molecule of 'Bad egg gas' is likely to be

tetrahedral pyramidal bent linear.

Check my Answers

Question 9:The correct answer is pyramidal.

Phosphorus is like nitrogen and has 5 valence electrons in its outer shell

This will be 1 pair and 3 singles - 3 bonds forming to 3 hydrogen atoms.

Using only 3 of the 4 orbitals means the shape will be pyramidal, like NH3.

Question 10:The correct answer is bent.

Sulfur is like oxygen and has 6 valence electrons in its outer shell

This will be 2 pairs and 2 singles - 2 bonds forming to 2 hydrogen atoms.

Using only 2 of the 4 orbitals means the shape will be bent, like H2O.

You answered them both correctly

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