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Three Pairs of Electrons

The maximum number of covalent bonds that can be formed by each atom sharing one of its electrons is equal to the number of outer shell electrons.For group 2 and 3 this may result in the empty orbitals being used for dative covalent bonds.Boron and aluminium have six electrons in the outermost shell in BF3 and AlCl3. As a result of the electron pair repulsion theory, the shape of the molecules is trigonal planar (flat) with a bond angle of 120° between the B-F and the Al-Cl bonds.

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Specification: AQA Chemistry (7404), AS-level, 3.1.3.5 Shapes of simple molecules and ions and 3.1.3.2 Nature of covalent and dative covalent bonds. Topic: Bonding.

Key terms in this lesson

Atomic orbital
A region in space around the nucleus where there is a 95% probability of finding an electron of a given energy.
Covalent bond
A strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
Electron pair repulsion theory
The theory that electron pairs around a central atom arrange themselves as far apart as possible to minimise repulsion, determining the shape of the molecule or ion.
Group
A vertical column of the periodic table, containing elements with the same number of outer-shell electrons.

More in Bonding

All 30 lessons in Bonding · All AQA AS-level Chemistry topics