What is a covalent bond?
2 marks · EasyExplain, using dot-and-cross diagrams, why a molecule of hydrogen fluoride (HF) contains only one covalent bond.
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Both hydrogen and fluorine atoms share one pair of electrons; hydrogen can only make one bond (having only one electron to share), and fluorine needs only one electron to complete its outer shell. The dot-and-cross diagram shows one shared pair.
Also accept: Both atoms only have one unpaired electron to share
Common mistakes: Claiming HF has more than one bond
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Marking points
M1 · 1 mark · States that hydrogen can only make one bond and fluorine needs only one electron to complete its outer shell.
A1 · 1 mark · References the dot-and-cross diagram showing only one shared pair of electrons between H and F.
Worked solution
Hydrogen has only one electron in its outer shell, so it can only share one electron (can only form one bond).
Fluorine has seven electrons in its outer shell and needs one more to complete it. Thus, the two atoms share one pair of electrons, forming a single covalent bond. In the dot-and-cross diagram, only one pair appears between H and F.