Structure of The Atom Notes

• The number of protons in one atom of an element is known as its atomic number.
• All the atoms of an element have same atomic number.
• It is generally denoted by the letter Z and written at the bottom of the symbol of that element.

Atomic number of an element = Number of protons in one atom of element

• Nucleus of an atom is composed of protons and neutrons which are collectively called as nucleons.

• Electrons have negligible mass so the entire mass of atom lies in its protons and neutrons which are present in the nucleus.

• Protons and neutrons have appox. 1 unit mass the sum of number of protons and neutrons is called the mass number of the atom.

Mass number = No. of protons + No. of neutrons

• The arrangement of electrons in the various shells (or energy levels) of an atom of the element is known as its electronic configuration.
• The maximum number of electrons which can be put in a particular energy level or shell was given by Bohr and Bury.

According to Bohr-Bury scheme:

1. The maximum number of electrons which can be accommodated in any energy level of the atom is given by 2n² (where n is the number of that energy level)

1. For 1^st energy level, n = 1

So, the maximum number of electrons in 1^st energy level = 2n²

= 2 × (1)²