Teacher's notes and answers to questions in the book - Hodder Plus ...

WJEC GCSE Additional Science Teacher’s Notes
14. How is water formed from hydrogen and oxygen
The oxygen atom shares one electron from one hydrogen atom and another electron from a
second hydrogen atom.
15. Why is water a liquid at room temperature
The freezing point of pure water is 0 °C and its boiling point is 100 °C, room temperature
(10–20 °C) is between these two values hence water is a liquid at these temperatures.
16. Why is water only a poor conductor of electricity
There are few H + and OH – ions in pure water – hence there are few charged particles free to
move and so water is a poor conductor of electricity.
17. Draw dot and cross diagrams showing the covalent bonds in the following molecules:
a hydrogen chloride c methane
b ammonia
18. Some atoms can form double covalent bonds. In these molecules, each atom shares four electrons (in
two pairs). Carbon dioxide is an example of a molecule containing double covalent bonds.
Draw dot and cross diagrams and structural formulae for the following molecules containing double
covalent bonds:
a sulfur dioxide
b oxygen gas
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