Displayed formulae
2 marks · EasyExplain why oxygen forms two bonds in the displayed formula of ethanol.
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Must show: Oxygen needs two more electrons to fill its outer shell, Oxygen typically forms two covalent bonds
Also accept: Oxygen has six electrons in its outer shell and needs two more
Common mistakes: Saying oxygen forms only one bond
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Marking points
M1 · 1 mark · Recognises oxygen forms two bonds to fill its outer shell.
A1 · 1 mark · Links to displayed formula of ethanol (e.g., bonds to hydrogen and carbon).
Worked solution
Oxygen forms two bonds in ethanol because it needs two more electrons to complete its outer shell. In the ethanol molecule, the oxygen atom forms one bond with the hydrogen (to make the -OH group) and one bond with a carbon atom.