Organichemica
Basic Organic Chemistry

A Tutorial

Dave Woodcock ©2001
Okanagan University College

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Level 1

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tetrahedral geometry

The four atoms surrounding a centre atom (with no lone pairs) are at the four courners of a tetrahedron. Bond angle between any two of the bonds to the four atoms is 109.5°.
Four electron groups spread out evenly in space produce groups pointing to the four corners of a tetrahedron. The shape obtained is called tetrahedral.
The geometry is explained electronically by using sp3 hybridization.
The carbon atom which has bonds to four other atoms is tetrahedral and is often called an 'sp3 carbon':


The tetrahedral (or sp3) carbon in methane.

trigonal planar

Three atoms surrounding a centre atom (with no lone pairs) are in a plane at 120° to each other.
Electronically, this geometry is explained by sp2 hybridization.
A highly reactive positive carbon species, the carbocation, has a trigonal planar geometry:


The trigonal planar (sp2) carbon in the methyl cation

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