How do you draw VSEPR diagrams?

1 Answer

Answer:

The Valence Shell Electron Pair Repulsion Theory (VSEPR) helps us to understand the 3D structure of molecules.

Explanation:

The general concept is that the pairs of electrons repel each other and try to locate themselves as far as possible from each other about a given nucleus.

Hence, for two pairs of electrons on a nucleus, the two pairs would locate themselves exactly opposite each other, forming a bond angle of exactly 180°.

If three pairs exist, they will locate themselves in a plane about the nucleus at angles of 120° from each other.

Here is a table of the electron pair geometries as a function of the number of electron pairs.

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To determine the shape of #"SO"_2#, for example, we first determine the Lewis dot structure of #"SO"_2#.

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The central atom, #"S"#, has three groups bonded to it, two oxygen atoms and a lone pair.

The electron pair geometry of #"SO"_2# is trigonal planar. It is drawn as

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The molecular geometry of #"SO"_2# is not trigonal planar.

In determining the molecular shape, we consider only the positions of the atoms, not the lone pairs.

So, the molecular shape of #"SO"_2# is bent and is represented as:

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The lone pair of electrons occupies a relatively large volume, since they are held by only one atom.

They compress the bond angle between the oxygens and sulfur to less than 120°. The actual #"O-S-O"# bond angle is 119.5°.

Here is a table listing the molecular shapes that correspond to various combinations of bonding pairs and lone pairs.

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