STD IX – ATOMIC STRUCTURE AND CHEMICAL BONDING – (Online)

Structure of an Atom

According to modern atomic theory, atoms are composed of particles. The three main sub-atomic particles are proton, neutron and electron.

Atomic Number

The number of protons in the nucleus of the atom of the element is the atomic number and denoted by the letter Z. In a neutral atom, the number of protons =  the number of electrons.

Atomic number = Number of protons.

Mass Number

This is the total number of protons and neutrons present in the atomic nucleus. It is denoted by the letter A

ELECTROVALENT BOND

Ionic bond, also called electrovalent bond, type of linkage formed from the electrostatic attraction between oppositely charged ions in a chemical compound. Such a bond forms when the valence (outermost) electrons of one atom are transferred permanently to another atom.

For example, the bond between the sodium and chlorine atoms in sodium chloride (NaCl) is formed by the transfer of an electron from sodium to chlorine, creating Na + and Cl – ions. The electrostatic attraction between these ions provides the bonding in NaCl.

COVALENT BOND

A covalent bond is formed by equal sharing of electrons from both the participating atoms. The pair of electrons participating in this type of bonding is called shared pair or bonding pair. The covalent bonds are also termed as molecular bonds. Sharing of bonding pairs will ensure that the atoms achieve stability in their outer shell which is similar to the atoms of noble gases.

Covalent Bonding can be Achieved in two Ways:

Sharing of electrons between atoms of the same kind E.g. Formation of H2, Cl2, O2, etc.

Sharing of electrons between atoms of different kind E.g. Formation of CH4, H2O, NH3, etc.