Reactivity

Key Stage 4

Meaning

Reactivity is how vigorously a chemical will react.

About Reactivity

Reactivity is determined by how easily an element can lose or gain electrons.

Electrons are held in orbit around the nucleus because the electrons are negatively charged and are attracted to the nucleus which is positively charged.

If an element loses electrons easily it is highly reactive.

If an element gains electrons readily it is also highly reactive.

Three important factors affect reactivity of elements.

• The charge of the nucleus
• The shielding effect of inner electrons.
• Distance between the nucleus and the outer shell.

Reactivity in Groups 1, 2 and 3

In a chemical reaction the electron in the outer shell is lost. The reactivity increases as you go down the group because: The outer electron is further away from the nucleus with each additional electron shell making the force of attraction weaker. This makes it easier for an atom to lose it's outer electron. Even though the charge of the nucleus increases the outer electron is shielded from most of the positive charge of the nucleus by electrons in the inner shells.

Reactivity in Group 7

In a chemical reaction an extra electron is added to the outer shell. The reactivity decreases as you go down the group because: The outer electrons are further away from the nucleus with each additional electron shell making the force of attraction weaker. This makes it less able to gain an extra electron. Even though the charge of the nucleus increases the outer electrons are shielded from most of the positive charge of the nucleus by electrons in the inner shells.

Reactivity along Period 2

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.

References

AQA

Reactivity; alkali metals, pages 26-27, GCSE Chemistry; Third Edition, Oxford University Press, AQA

Reactivity; metals, pages 26-27, 84-89, 220-221, GCSE Chemistry; Third Edition, Oxford University Press, AQA

Reactivity; periodicity, pages 19, 30-31, GCSE Chemistry; Third Edition, Oxford University Press, AQA