Covalent bonding, shapes and electronegativity
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 3 practice questions, 4 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Why water is bent
- Covalent bonds and dot-and-cross diagrams
- Coordinate bonding
Read the transcript of the teaching part
Last time
Before we start: last time, in Equations, formulae and the mole, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Why water is bent
Carbon dioxide is a straight line, but water is bent. Both have three atoms, yet their shapes are completely different, and so are their properties. Water is a liquid that dissolves salts, and carbon dioxide is a gas. The difference is down to lone pairs of electrons, and how they repel.
Covalent bonds and dot-and-cross diagrams
A covalent bond is the electrostatic attraction between the nuclei of two atoms and a shared pair of electrons. A dot-and-cross diagram shows only the outer electrons. Use dots for one atom's electrons and crosses for the other's. A bond pair is shared. A lone pair belongs to one atom. Show both. An ionic compound like lithium oxide shows square brackets and charges: two Li plus ions, and one O two minus ion with eight outer electrons.
Coordinate bonding
A coordinate bond, or dative covalent bond, is a covalent bond in which both shared electrons come from the same atom. The donor has a lone pair. The acceptor has an empty orbital, or is positively charged. In the ammonium ion, the nitrogen lone pair of ammonia is donated to a hydrogen ion, H plus. Once formed, a coordinate bond is identical to the other bonds. Show it as an arrow from the donor.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Bond angles.
The whole chapter: Chemical Bonding, Chemical Bonding.
Chapter 3: Chemical bonding
- Covalent bonding, shapes and electronegativity 7 min
- Hybridisation, sigma and pi bonds 7 min
- Intermolecular forces and metallic bonding 7 min
Also for A Level Chemistry 9701
Which topics come up most in A Level Chemistry 9701 past papers, counted from every paper since 2004: Paper 2 topic frequency, Paper 4 topic frequency.