Return to Contents Chapter 1: Structure Determines Properties Ch 1 contents
Bonds

There are three bonding situations that we need to be aware of, these are:

ionic bonds, covalent bonds and polar covalent bonds

Each type will be encountered during our journey through organic chemistry.

Ionic bonds result when electrons are transfered between atoms forming ions.
The electron donor will become a positively charged ion =  cation
The electron acceptor will become a negatively charged ion = anion
The ionic bonds then result from the non-directional, electrostatic interaction between the ions based on simple electrostatics.
General rule:  Ionic bonds are formed when the electronegativity difference (Δχ) between the atoms is > 1.7

Covalent bonds result when valence electrons are shared between atoms.  A covalent bond is a balance between the attractive and repulsive forces between the atoms which ends up placing electron density between the atoms.
General rule:  Covalent bonds are formed when the electronegativity difference (Δχ) between the atoms is < 1.7

Polar covalent bonds result when the valence electrons are not shared e&ielta;mportant to note that unless Δχ = 0, there is unequal sharing of the electrons. This leads to a bond polarity or a bond dipole.

In organic compounds the C-C and C-H bonds are regarded as non-polar since the electronegativities are similar C (2.5) and H (2.1)

Most bonds within organic molecules will be covalent.  The exceptions will be compounds which possess metal atoms (where the metal atoms should be treated as ions, e.g. CH3MgBr = CH3- Mg2+ Br- and CH3ONa = CH3O- Na+).

You should be able to identify whether an ionic or covalent bond is being formed between atoms.  If a bond is covalent you should be able to identify whether it is polar or non-polar.


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© Dr. Ian Hunt, Department of Chemistry, University of Calgary