Group 17: The Halogens


The Halogens in Group 17 are non metal elements that are diatomic and simple covalently bonded. They decrease in reactivity down the group but increase in their melting and boiling points.

The halogens are found in Group 17 including fluorine, chlorine, bromine and iodine. They are considered to be the most reactive non metals. Halogens unlike metals exist in a number of states from fluorine as gases to the larger iodine as a solid. Halogens exhibit increasing reactivity up the periodic table. The halogens are so reactive due to their need to gain an extra electron to complete their shell of 7 electrons to 8. By obtaining an electron the halogens will form -1 charged halide ions. The reactivity of the halogens increases up the group as fluorine is the smallest atom and has a small atomic radius, this means it is able to easily attract an electron through its low number of shells.

Terms in section

Halogens are found in group 7 of the periodic table. Non metal elements that have 7 electrons in their outer shell and are often used for cleaning or sterilization.


How an element or compound will easily gain or lose electrons when interacting with other elements. Reactivity can also be a measure of how violent a reaction is giving our heat or light.


Halides are ionic compounds formed when metals react with halogens to form ionic compounds


An ion forms when an atom loses or gains electrons to form a positive or negative particles due to the unbalanced number of protons

Atomic radius

Atomic radius is the distance measured from the nucleus to the outer valence electrons – measured in pm picometres which is 1x10-12 m


The shell is the path that electrons follow outside the nucleus. Shells can be considered as energy levels and the further away from the nucleus the higher in energy.


The Transition Metals


Group 18: The Noble Gases