Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

Example 2- I:

The sulphur hexafluoride molecule in Lewis structure

A SF 6 molecule consists of one sulphur atom and six fluor atoms. We wish to write down the Lewis

structure for this molecule in order to know something about the internal atomic arrangement and the

positions of the lone pairs in this molecule. Thus the 3-step procedure given by (2- 2) on page 59 is used

again:

Number of valence electrons = 6 (from sulphur) + 6×7 (from fluor) = 48

Use one electron pair pr. S-F bond. Since sulphur is from the 3rd period it can be surrounded by more than

eight electrons.

The remaining 48 - 6×2 = 36 electrons are arranged so that the octet rule is satisfied for all fluor atoms.

Figure 2- 11: Lewis structure for the sulphur hexafluoride molecule

The three steps in writing the Lewis structure. The octet rule has to be satisfied for all the atoms in the

molecule. Sulphur from the 3rd period has the ability to be surrounded by more than eight electrons pairs

by using its empty 3d-orbitals.

From the Lewis structure we now know that the sulphur atom is placed in the centre and is bonded to the

six fluor atoms by single bonds. Furthermore we know that each fluor atom is surrounded by three lone

pairs. But from the Lewis structure we know nothing about the actual geometry of the molecule.

The 3-step procedure given by (2- 2) on page 59 can also be applied for composite ions such as sulphate,

nitrate, cyanide etc. We are going to look more into that in the following example where the Lewis structure

for nitrate will be written down. During this procedure we will run into the concept of resonance structures.

Chemical compounds