Atomic Structure

The central nucleus is made up of PROTONS and NEUTRONS. The nucleus is surrounded by electrons which are arranged in shells.

An atom has the SAME number of PROTONS and ELECTRONS, therefore it has no electrical charge.

The relative and charge mass of Protons, neutrons and electrons.

Atomic Particle Relative Mass Relative charge

Proton 1 +1

Neutron 1 0

Electron 1/1836 -1

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Atomic and Mass number

Atomic number - number of protons in an atom.

Mass number - total number of protons and neutrons in the nuclei.

MA - mass number is the top and atomic is the bottom.

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Isotopes

Atoms of the same element that have same atomic number but different mass number.

Each Isatope has the same number of protons and electrons but different number of neutrons.

For example, Carbon has three.

Isatope symbol Mass no. Atomic no. Protons neutrons electrons

C-12 12 C 6 12 6 6 6 6

C-13 13 C 6 13 6 6 7 6

C-14 14 C 6 14 6 6 8 6

Isotopes have different physical properties because they have different masses but same chemical properties because the electronic configuration doesnt change.

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Relative atomic mass

The larger of the two numbers (top) number is the Ar.

The relative atomic mass is the mass of a particular atom compared with a twelfth of the mass of a carbon twelve atom.

Calculation

(Mass x % isotope 1) + (Mass x % isotope 2)

100

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Electronic Configuration

Shows how the electrons are arranged in shells around the nucleus: 2,8,8,2

The outer shell is important because it tells us how an atom bonds to other atoms.

The group number tells us how many electrons are in the outer shell.

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Relative formula mass

Relative formula mass of a compound is the sum of the atomic masses of all the atoms in the formula.

E.g

H2SO4

H = 2 x 1 = 2

S = 1 x 32 = 32

O = 4 x 16 = 64

Add all together = 98

98 is the mass number for H2SO4

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Atomic Structure