Civil Engineering Reference
In-Depth Information
with the mucous membranes is also a question of chemistry. It has been shown
that certain materials react with each other, and can thus affect each other's dura-
bility, pollution potential, etc.
A small introduction to the chemistry of building
materials
There are a total of 89 different chemical elements in nature. Each element is rep-
resented by a single letter or two letters, e.g. H for hydrogen or Au for gold.
Chemistry is mainly concerned with the way these elements combine to form
compounds.
Materials usually consist of several compounds, and when a product consists
of several materials the picture can become rather complex. A telephone can
contain as many as 42 of the 89 elements (Altenpohl, 1980). Materials exist as
solids, liquids or gases. The same chemical compound can exist in any of these
three states, depending on temperature and pressure. Water (H
2
O) freezes at
0°C and boils, or evaporates, at 100°C without changing its chemical composi-
tion.
The smallest unit a material can break down into is a molecule. Every molecule
consists of a certain number of atoms. These atoms represent the different ele-
ments and can be obtained through chemical reactions.
Relative atomic weight
Each of the 89 elements has its own characteristic atomic structure, mainly
described by its weight: the relative atomic weight. Hydrogen has the lowest rel-
ative atomic weight, 1, while oxygen has a relative atomic weight of 16.
The molecular weight of water is found through adding up the different
atomic weights:
H
2
O = H + H + O = 1 + 1 + 16 = 18
(1)
Calcium carbonate (CaCO
3
) consists of calcium (Ca), with a relative atomic
weight of 40, carbon (C) with a relative atomic weight of 12, and oxygen (O) with
16. The relative molecular weight is therefore:
CaCO
3
= Ca + C + O + O + O = 40 + 12 + 16 + 16 + 16 = 100
(2)
The relative atomic weights of the different elements are given to two decimal
places in the periodic table (see Figure 4.1). The elements are also given a rank-
ing in the table of 1-89. The number of the elements in the ranking order is equiv-
alent to the number of protons in the nucleus of the atom.
