Common Molecular Structures
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There are a few basic molecular structures.
In order to picture them, you need to be able to see three-dimensionally.
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In a linear molecule, the atoms lie in a straight line.
The bond angle formed is therefore 180°.
Planar Triangular Molecules
In a planar triangular molecule, three atoms extend out from a central atom.
All four atoms lie on the same plane and the bond angles are all 120°.
A tetrahedron is a four-sided geometric figure shaped like a pyramid with triangular faces.
A tetrahedral molecule is a molecule which has four atoms extending out from a central atom.
The four atoms are located at the vertices of a tetrahedron.
All bond angles are 109.5°.
Trigonal Bipyramidal Molecules
This shape consists of two trigonal pyramids (pyramids with triangular faces) stuck together by their bottoms.
The central atom has 3 atoms which extend out all on the same plane.
These are called the equatorial bonds and have a bond angle of 120°.
Perpendicular to that plane are 2 atoms extending in opposite directions.
They are the axial bonds.
An octahedron is an eight-sided figure.
It is like two square-bottomed pyramids sharing a common base.
It has six verticies with atoms all extending from a central atom.
If it was on a three-dimensional coordinate grid with the central atom being the origin, the bond extensions would run along the x-, y-, and z-axes.
All bond angles are 90°.