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Electronic configuration, electronic structure and electronic arrangement all mean the same thing.

Electrons orbit the nucleus in shells.

• each shell is at a different distance from the nucleus. The first shell is nearest to the nucleus.
• different shells hold a different maximum number of electrons.
• the electrons fill the lowest available shell first – the one nearest the nucleus.
• when this shell is full, the electrons begin to fill the next shell.

The table below shows the maximum number of electrons each shell can hold for elements with atomic numbers 1 to 20.