Structure of atoms, molecules and chemical bonds


The Atoms – Nature’s Building Material

All the living organism and non-living objects are formed of matter. Atoms are the building block of matter. Atoms are generally formed of three subatomic particles: electron, proton, and neutron. Each electron has one unit negative charge and each proton has one unit positive charge, whereas a neutron has no charge. Atoms aggregate and form elements so and an atom is the smallest part of an element.When the atoms are charged, then these are called ions which are of two types :

  1. The cation is a positively charged atom e.g. Na+, K+.
  2. The anion is a negatively charged atom e.g. Cl.

An element is the simplest form of matter which cannot be split into two or more simpler substances by ordinary chemical methods because an element is formed of only one type of atom.

There are only 25 elements essential to life which are divided into three categories:

  1. Principle or major elements
  2. Minor elements
  3. Trace or Rare elements

Principle or major elements

These are four in number e.g. Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N). These form about 95% of total amount of minerals.

Minor elements

These are nine in number e.g. Sodium (Na), Potassium (K), Calcium (Ca), Magnesium (Mg), Iron (Fe), Sulphur (S), Phosphorus (P), Iodide (I), and Chloride (Cl).

Trace or Rare elements

These are twelve in number e.g. Cu, Co, Mo, Cr, Mn, Ni, Zn, Si, Sn, As, F, and Br.

About 98 percent of the body weight of an organism is composed of only six type of elements (e.g. C, H, N, O, P and S).

Though the trace elements are required in very small quantities but are very essential nutrients of the organisms for the normal functioning of metabolism e.g.


Iodine is an essential component of thyroxine hormone secreted by the thyroid gland and controls basal metabolic rate (BMR) so regulates the physical, mental and sexual growth of the children. Daily need of iodine in the human diet is 0.02 mg. Deficiency of iodine in the diet leads to goiter disease in adult and cretinism in children.


Iron is the component of hemoglobin of RBCs of blood and helps in transportation of oxygen (about 97-99%) as well as carbon dioxide (about 23%). Deficiency of iron cause anemia.


Molybdenum is essential for the functioning of enzyme Nitrogenase in the leguminous plants and helps in biological nitrogen fixation.

Carbon is the principal structural element of a living cell.