Lewis structures can be used to predict the 3-dimensional shape of a molecule by using a simple theory known as VSEPR: Valence Shell Electron Pair Repulsion
We know that electrons repel each other, since they have like charges. VSEPR theory states that the electrons in a molecule repel each other, so the orbitals containing those electrons are oriented as far away from each other as possible.
In the simplest example, consider the molecule BeH₂, beryllium hydride. BeH₂ has two bonds, one between each hydrogen and the beryllium, and no lone pairs. Its Lewis structure is



The electrons in the two bonds repel each other, thus, they will be as far apart as possible. Therefore, the hydrogens will be on opposite sides of the beryllium and the molecule is linear, with an angle of 180⁰ between the two bonds. The Chime model below shows the BeH₂ molecule.
VSEPR can be used to predict the structures around atoms with more than two things attached: for example, the methane molecule CH₄ has the four hydrogens at the tips of a tetrahedron, with the angles between the bonds = 109.5⁰.
Double and triple bonds act exactly like single bonds for VSEPR purposes. Lone pairs affect the molecular geometry, but VSEPR does a good job predicting structures with lone pairs as well. For a molecule with one or more lone pairs

• A lone pair acts much like a bond for arranging things around the atom. It repels bonds much like a bond would.
• The molecular geometry is quite a bit different than the species without the lone pair. The lone pair is not included in the molecular geometry. See the links below for examples.

The links below will give you models of the various molecular geometries. A useful shorthand to write the type of geometry is the AX_mE_n notation, where A is the central atom, surrounded by m X things and n lone pairs.

• AX₂: Linear
• AX₃: Trigonal Planar
• AX₄: Tetrahedral
• AX₅: Trigonal Bipyramidal
• AX₆: Octahedral

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