Chemistry, Third edition

5 · MORE ABOUT BONDING

The three electron pairs around boron minimize the repulsion between them

when the molecule adopts the trigonal planarshape. The fluorine atoms are in the

same plane, at the three corners of a triangle drawn around the central atom. The

three angles between the B–F bonds are all 120°.

3. Methane, CH 4

To minimize repulsion, the four electron pairs adopt a tetrahedralshape, with a

bond angle of 109° 28:

4. The PF 5 molecule

The five electron pairs adopt a trigonal bipyramidalshape, with bond angles of 120°

and 90°:

5. The SF 6 molecule

In this molecule the six electron pairs arrange themselves in an octahedralshape. All

bond angles are 90°.

To summarize, Table 5.1 shows the shapes adopted by covalent compounds with

different numbers of electron pairs around the central atom.

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