BAKER HUGHES - Drilling Fluids Reference Manual

Oil / Synthetic Fluids
charged (represented by Cl – ). Negatively charged ions are called anions. Sodium chloride can be
represented as Na + Cl – to indicate the electron transferred.
The two electrically charged atoms or ions of opposite charge are highly attracted to one another. This
electrical attraction is called coulombic attraction. When atoms in a molecule have somewhat similar
affinity for the electrons, the bond is covalent and the molecules are nonionic. The shared electrons
are distributed over the atoms. Examples would be molecular hydrogen, molecular nitrogen, and
hydrocarbons.
Fundamental Chemical Classes
If the electrons in a chemical bond are shared equally by the atoms, we call the bond nonpolar. An
example would be molecular nitrogen. When the shared electrons in a molecule favor one atom over
the other, the bond and the molecule are polar. An example is water. Polar molecules, while
electrically neutral, have uneven centers of positive and negative charge due to the uneven electron
distribution. Such molecules are called dipoles. Hydrogen chloride (gas) is a good example (see
Figure 5-2).
Figure 5-2
Dipolar Hydrogen Chloride Molecule Showing Separation of Charge
The positive end of one dipole is attracted to the negative end of other dipoles. This is referred to as
dipole interaction and this phenomenon accounts for much of the strong attraction that polar molecules
have for each other (see Figure 5-3).
Figure 5-3
Association of Liquid Water
Baker Hughes Drilling Fluids
Reference Manual
5-8 Revised 2006