Atomic Structure

Atom is the smallest particle of an element that may or may not exist independently.
E.g. Iron (Fe), calcium (Ca) and hydrogen (H).

Molecule is the smallest particle of an element or compound that exists independently.
E.g. Oxygen (O₂), nitrogen (N₂) and water (H₂O).
Mole is the collection of 6.022140857 × 10²³ particles.
1 mole = Avagadro's number = 6.022140857 × 10²³.
1 mole atom = 6.022140857 × 10²³ atoms.
1 mole molecule = 6.022140857 × 10²³ molecules.

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Constituents of the Atom

Constituents of the atom are proton, neutron and electron.

1. Proton

• Discovered by Goldstein and named by Ernest Rutherford.

2. Neutron

• Discovered by James Chadwick.

3. Electron

• Discovered by J.J. Thompson and named by Johnstone Stoney.

p = No.of protons
n = No.of neutrons
e = No.of electrons
Atomic number (Z) = p = e
Mass number (A) = p + n
Atomic symbol = X
Representation:
${}_Z{}^{A}X$ .
In
${}_{\mathrm{15}}{}^{\mathrm{31}}P$ ,
Z = 15,
A = 31,
n = Z - A = 31 - 15 = 16
Isotopes has same atomic number but different mass number.
E.g.
${}_7{}^{12}N$ ;
${}_7{}^{14}N$ ;
${}_7{}^{16}N$ .
Isobars has same mass number but different atomic number.
E.g.
${}_6{}^{14}C$ ;
${}_7{}^{14}N$ .
Isotones has same number of neutrons.
E.g.
${}_{15}{}^{31}P$ ;
${}_{16}{}^{32}S$ .