Period (Chemistry)

Key Stage 3

A period is a row on the Periodic Table whose elements all have the same number of Electron Shells.

Atomic Number increases as you move along a period.

The chemical and physical properties of elements change as you move along a period.

Period 2 Melting Points	Period 3 Melting Points

There is a trend in the Melting Points as you move along the period.	A similar trend can be seen in the next period.

A period is a row on the Periodic Table whose elements all have the same number of Electron Shells.

Atomic Number increases as you move along a period.

The number of the period is the same as the number of electron shells.



For the first 3 elements Lithium, Beryllium and Boron all lose electrons in chemical reactions. The reactivity decreases as you go across the period because: The outer electrons are all roughly the same distance away from the nucleus. The charge on the atomic nucleus increases as you move go across the period but the electron shielding caused by the two inner electrons remains the same. This causes the electrons to experience a greater force of attraction as you move along the period, making it harder for the atoms to lose electrons and become ions. Nitrogen, Oxygen and Fluorine can all gain electrons to become negative ions in certain reactions. The reactivity increases as you go across the period because: The outer electrons are all roughly the same distance away from the nucleus. The charge on the atomic nucleus increases as you move go across the period but the electron shielding caused by the two inner electrons remains the same. This causes the electrons to experience a greater force of attraction as you move along the period, making it easier for an atoms to gain more electrons to become ions.