Most probably not all chemical elements existing in
the Universe, Sun and Earth (Table 1) have taken part in the
build-up of living organisms. Their composition differs a lot
from non-living nature which indicates to a chemistry of a
special type. Living entities contain only a definite number
of chemical elements. Our knowledge on that matter is
constantly being enriched and undergoes changes including
new elements. Only before several decades it was thought
that the basic organic elementsare four — carbon (C),
hydrogen (H), nitrogen (N) and oxygen (O). Later on two
others were added — phosphorus (P) and sulphur
(S). The rest of the elements participate in much smaller
quantities and depen-ding on their percentage con-tent they
are divided into macroelements (0.5—1%) and microelements (0.01—0.001%).
Figure 1–4. Structure of water. The general shape of the water molecule is governed by
the shapes of the outer electron orbitals of the oxygen atom. These orbitals, like the bonding
orbitals of carbons, are roughly tetrahedral in shape: a single hydrogen atom is placed at
two corners and unshared electrons at the other two. Because the oxygen nucleus
attracts electrons more than hydrogen does, the water molecule is dipolar. Thus, the hydrogen
nuclei are slightly positively charged and the oxygen nucleus slightly negatively
charged. Other water molecules can fleetingly join together to create a lattice of water
molecules held together by hydrogen bonds. This short-lived ensemble has been called a
flickering cluster, which represent a prerequisite for emergence of living matter.
