Basic Physical Chemistry

An atom consists of a positively charged nucleus (protons, neutrons) surrounded by a single negatively charged electron (hydrogen) or ‘shells’ of electrons. A molecule consists of two or more atoms joined by chemical bonding. Bonds vary in type and the strength of bonding depends upon the participation atoms and upon other interactions between molecules (inter-molecular), or within a molecule (intra-molecular).

In order of increasing strength of bonding:

Intermolecular Van Der Waals bonds are weak and operate over short distances.

Non-covalent bonds result from electrostatic attraction of charged groups in molecules.

Hydrophobic attraction involves an orientation of un-charged molecules toward un-charged components of the medium and away from charged components, such as water.

A hydrogen bond results from an attractive intermolecular force between two partial electric charges of opposite polarity. Although stronger than most other intermolecular forces, a hydrogen bond is much weaker than either a covalent or ionic bond.

In covalent bonds, atoms share an electron or electrons.

In ionic bonding an atom donates an electron to another atom.