BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
Atomic weight
Carbon has six protons (each of mass 1 a.m.u.) in its nucleus and thus has atomic number 6.
Most carbon atoms have six neutrons (also each of mass 1 a.m.u.) in their nucleus and the atomic
weight of one atom of this type of carbon is defined as 12.00000 a.m.u. The mass of the electrons
is included in this figure, but their contribution to the total is very small. All other elements are
compared to this on a relative scale.
Atomic weights for all the elements are given to the nearest 0.01 a.m.u. in Table 3-1. At this
level of accuracy, the mass of the electrons is negligible. Thus, the atomic weights might be
expected to be whole numbers, since they are simply the sum of the number of protons and
neutrons in the nucleus. Table 3-1 shows that this is not so. The explanation is that atoms of the
same element can have different numbers of neutrons in their nucleus and thus different atomic
weights. For example the majority of carbon atoms have 6 neutrons but some have 7 or even 8
making their atomic weight 13 or 14 respectively. The atomic weight of the element carbon is an
average of all the forms that occur, taking into account their relative abundance in nature, and is
thus 12.01.
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 3-3