water formula

Chemistry and its Language

Every science has its own technical terms and usually it requires considerable effort on the part of a beginner to master them. Chemistry is no exception. It is full not only of technical terms but also of c expressions like H2O, H2SO4 etc., which is the language of chemistry stand for the names of certain definite chemical substances. Before we walk up this language, we must understand some of the important technical terms which we shall come across.



 The smallest forms of matter which cannot be decomposed into simpler substances are called elements. We always come across such elements in our daily life. Hydrogen, oxygen, iron, silver, etc., are its examples.

 Element table



           Compound Of CO2

A compound is a substance of the other kind. When two or more elements combine chemically, i.e., in such a way that the properties of the resulting substance are entirely different from those of the combining elements, a chemical compound is obtained. It can be decomposed into simple substances by suitable chemical methods at our disposal. Water and carbon dioxide are examples of compounds.


The smallest particle of an element which can take part in chemical change is called an atom. It may or may not be capable of independent existence. There are 105 elements. Scientists say that atom has a fixed shape. There are smaller particles present inside the atom called sub-atomic particles. The sub atomic particles are
a) Electron       b) Proton and   c) Neutron

carbon atom

Name of subatomic
Relative weight
Relative charge
+ve 1
0 (null)
1839   of an atom of Hydrogen
-ve 1

Atomic Weight

Atoms are so small particles that their weights are inconveniently small in terms of grams, i.e., gram is too big to weight an atom or a molecule. For example, the weight of carbon atom is 0.00000000000000000000000195g (1.95×10-23g). to overcome this difficult, one-twelfth of the weight of a carbon atom (12c isotope) is selected as a unit of weight for the purpose and is termed 1 atomic mass unit (1amu).
Atom of the same element may have different masses. These are called isotopes. For example, chlorine has two isotopes of weight 35 amu and 37 amu. These are mixed in such a proportion that their average weight is 35.5 amu. Such an average is called atomic weight of the element. Atomic weight is defined as the average mass of the atoms of an element expressed in atomic mass units, carbon-12 being taken as the standard with an atomic mass of 12 amu. By saying that atomic of magnesium is 24, we mean that an atom of magnesium is twice as heavy as an atom of carbon.


The smallest particle of matter which is capable of stable existence is called molecule. A molecule is in a state of stability. Molecule of element or compound cannot be seen through naked eyes.

Molecular weight

The molecular weight of an element or a compound is defined as the relative weight of its molecule as compared with that of carbon atom (12c isotope) taken as 12 amu.
It is only a number and gives only a relative weight of the molecule. It does not give the actual weight of the molecule at all. Molecular weight of magnesium carbonate is equal to 84 means that a molecule of magnesium carbonate is 7 times heavy as an atom of carbon or 84 times as heavy as one-twelfth of an atom of carbon.

 Atomic number

Proton and electron are electrically positively and negatively charged respectively. Proton and neutron are located in the nucleus. An atom is electrically neutral because number of protons in the nucleus is equal to the number of the electrons in the orbits. That is, number of protons in an atom is equal to number of electrons. Because of variation in atomic number and the weight the properties of elements are different.
Atomic number of an electrically neutral atom of an element is defined as the number of protons or the number of electrons.
There are 105 elements. The atomic number also increases from 1 to 105. The atomic number determines the characters of an element.

Electronic Configuration

 Protons and neutrons are located in the nucleus of an atom. Electrons revolve round the nucleus like negatively charged cloud. The planetary electrons can be compared with solar system. As different planets revolve around the sun in their fixed orbits, the electrons also revolve the nucleus in the fixed paths called orbits, shell or energy level. These energy levels can be one or more. The shells which are closer to the nucleus are low energy level and farther the orbits higher the energy level. The number of electrons in an orbit can be given by the following rules which are called as Bohr-Bury Scheme.
The maximum number of electrons in an orbit is given by formula 2n2, where n is the number of orbits.
The outermost orbits shall not have more than eight electrons and next to the outermost not more than 18.
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