Chem- Understanding Atomic Structure and Electron Configuration

Atom

An atom is the smallest part of an element that retains the properties of that element.

Proton

Charge: +1, Mass: 1, Location: Nucleus

Neutron

Charge: 0, Mass: 1, Location: Nucleus

Electron

Charge: -1, Mass: Almost 0, Location: Shells around nucleus

Nucleus

Tiny compared to the atom and very dense — contains almost all the mass.

Atomic number

Number of protons = number of electrons (in a neutral atom).

Mass number

Number of protons + neutrons.

Number of neutrons

Mass number − Atomic number

Sodium (Na)

Atomic number = 11, Mass number = 23, Protons = 11, Electrons = 11, Neutrons = 23 - 11 = 12

Magnesium (Mg)

Atomic number = 12, Electrons = 12, Electronic structure: 2 electrons in 1st shell, 8 electrons in 2nd shell, 2 electrons in 3rd shell → 2, 8, 2

1st shell

Maximum 2 electrons

2nd shell

Maximum 8 electrons

3rd shell

Maximum 8 electrons (for GCSE)