Chapter 1: Structure Determines Properties

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.

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