- One atomic mass unit is a mass unit equal to exactly one twelfth(1/12th) the mass of one atom of carbon-12
10.Relative atomic mass of the atom of an element is defined as the average mass of the atom, as compared to 1/12th the mass of one carbon-12 atom
11.it is most elements are not able to exist independently. Atom form molecules and ions
- A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance
- Molecules of element are formed by the atoms of the same type
- Atoms of different elements join together in definite proportions to form molecules of compounds
Based upon atomicity we can classify molecules as follows.
- Monoatomic molecules: Noble gases like helium, neon, argon, etc., exist in atomic forms, i.e., they are monoatomic. For example, helium, neon and argon exist as He Ne and Ar respectively.
- Diatomic molecules: These molecules consist of two atom. For example, hydrogen (H2 ) oxygen (O2), nitrogen (N2), chlorine (Cl2), carbon monoxide (CO), hydrogen chloride (HCl) and sodium chloride (NaCl).
- Triatomic molecules: These molecules consist of three atom. For example. ozone (O3) is a triatomic molecule. Similarly, carbon dioxide (CO2), nitrogen dioxide (NO2) and hydrogen sulphide (H2S) are examples of triatomic molecules.
- Tetraatomic molecules: These molecules consist of four atoms. For example, P4 is a tetraatomic molecule of phosphorus.
- Polyatomic molecules: Any molecule containing more than four atoms is called a polyatomic molecule. For example, sulphur (S8), methane (CH4), nitric acid (HNO3), ethanol (C2H5OH).