BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
A molecule is the smallest particle of a compound which can exist and still retain the same
chemical properties of that compound. Molecules consist of atoms chemically bonded together in
a precise arrangement. A molecule of water consists of two atoms of hydrogen combined with
one atom of oxygen to give a chemical formula of H 2 O. When the elements hydrogen and
oxygen combine to form the compound water, each molecule of water consists of two atoms of
hydrogen bonded to one atom of oxygen.
Atomic structure
Atoms are indivisible by chemical means, but other methods show that they are composed of
three simpler particles. These are neutrons, protons, and electrons.
Neutrons have no charge and are assigned a mass of one atomic mass unit, or 1 a.m.u., but carry a
single positive charge. Electrons are much lighter, being only 1/1840 a.m.u. They carry a single
negative charge.
Figure 3-1
Pictorial Representation of Atomic Structure
The simplified picture of an atom is that of a dense nucleus containing all the neutrons and
protons surrounded by a diffuse “cloud” of electrons which orbit the nucleus in various electron
“shells” or orbitals. Thus the nucleus carries all the positive charge of the atom and negative
charge is spread over a comparatively much larger area by the electron cloud. The electrons are
equal in number to the protons so that overall the atom is electronically neutral.
Atomic number
The number of protons in the nucleus is called the atomic number and determines the identity of
an atom. There are over a hundred different elements, each characterized by a different number
of protons in the nucleus of their atoms. Hence each element has a different atomic number.
Most elements are found in nature, though some only exist on earth by virtue of artificial
synthesis in a nuclear reactor.
The terms “atom” and “element” are often mixed up or left out when referring to elements by
name. Thus “Iron has a density of 7.7” refers to the element but “Iron has an atomic number of
26” refers to the atoms of the element iron having 26 protons in their nucleus.
Lists of atomic numbers are given in Table 3-1.
Reference Manual
Baker Hughes Drilling Fluids
3-2 Revised 2006