An atom consists of a central small nucleus which contains the proton and the neutron and is surrounded by electrons in an orbit. There is an electrostatic force of attraction between the positively charged nucleus and the negatively charged electrons. The maximum number of electrons a shell can accommodate is given by 2n2, n is an integer
n = 1, 2 x 12 = 2
n = 2, 2 x 22 = 8
n = 3, 2 x 32 = 18
An atom is represented by the symbol where A – mass number, Z – atomic number
Atomic number of an atom is the number of protons in the nucleus of an a atom.
The mass number is the number of protons and neutrons in the nucleus of an atom
The number of neutrons, N = A-Z,
The proton is positively charged, the neutron has no charge but the electron is negatively charged
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