An element is a substance which cannot be further divided into simpler substances.  Over 100 chemical elements are known.  They fall into two main categories, namely: Metals and Non-metals. Metallic elements have their ending with letter M while non-metal element may not have named ending with letter M but with other alphabets except very few.



Chemical compounds are formed when two or more elements combine together.  On this basis, two major categories of chemical compounds are known:  (a) Binary Compound    (b) Non-Binary Compounds.


Their names end with-ide Their names often end with-ate
They are made of only two elements They are made of 3 or more elements



Hydrogen H             Sodium, Na

Helium, He               Magnesium, Mg

Lithium, Li                 Aluminium, Al

Berilium, Be             Silicon, Si

Boron, B                    Phosphorous, P

Carbon, C                 Sulphur, S

Nitrogen, N              Chlorine, Cl

Oxygen, O                Argon, Ar

Flourine, F                Potassium, K

Neon, Ne                  Calcium, Ca



Water                        H20

Sand               Si02

Chalk              CaC03

Lime               CaO


The elements in a chemical compounds cannot easily be separated for they are chemical combined.  The ratios of combination of atoms of these elements in compounds are fixed unlike in mere mixture.



Binary Compounds are compounds of elements only and names ending with-ide.  E.g. Magnesium chloride. Magnesium Chloride = Magnesium + Chlorine.

Elements Atomic Electronic Number Group Configuration Valency Oxidation number
H 1 1 1 +1
He 2 2 0 0
Li 3 2,1 1 +1
Be 4 2,2 2 +2
B 5 2,3 3 +3
C 6 2,4 4 +4
N 7 2,5 3 -3
O 8 2,6 2 -2
F 9 2,7 1 -1
N 10 2,8 0 0


Combinations of elements are made on the basis of their combining Capacities called valencies. Besides, every atom of element contain electrons by which distribution in a given order termed ELECTRONIC


CONFIGURATION, the group and hence valency of each element in combination is decided.  For example, Magnesium nitride.

Mg = 12 = 2, 8, 2 = Group = 2, valency = +2

N = 7= 2 , 5 = Group = 5, valency = -3


Mg          N   = Mg3 N2 = Magnesium nitride.


2              3


Fundamental particles of Atom

The atom is made up of a number of different particles.

There are three fundamental units namely;

  1. The electron (discovered 1897)
  2. The proton (discovered 1920)
  3. The neutron (discovered 1932)



The electron carries a negative electric charge and indeed a very small function of the mass of even the smallest atom, hydrogen. They are at a comparatively great distance from the centre of the atom and travel rapidly and continuously in orbits around its centre known as the nucleus. The electrons were discovered first in 1897 by Sir J.J. Thomson.



The proton is a positively charged particle found in the nucleus of an atom although the positive charge on the proton has same magnitude charge on the electron mass of the proton which is about 1800 times larger than that of the electros.

The number of protons in the nucleus of an atom is called atomic number. All atoms of the same element have the same atomic number but those of different elements have a different number of protons in their nuclei. The sum of the protons and neutrons in the nucleus of an atom is called the mass number with the symbol. The proton was discovered by Sir, Ernest Rutherford in 1920.



The neutron was discovered in 1932 by a British Scientist, James Chadwick. It has almost the same charge. Whenever the neutron number in the nucleus of an atom of the same element varies, its mass number also varies and hence we have ‘Isotopes’.

Isotopes are atoms of elements of the same atomic number but different mass number because of the difference in their neutrons number. The three common isotopes of hydrogen are:

  1. Proton – 1 proton
  2. Deuterium – 1 Proton + 1 neutron
  3. Tritium – 1 Proton + 2 neutrons

The particles proton and neutrons which make up the nucleus are – called Nucleons


See also

Water and Chemical Pollution

Air and Noise Pollution

Environmental Health

Classes of food


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