Group 7 and Period 3

The PeriodicTable

Group 7 and Period 3

The halogens

Iodine

Bromine

Chlorine

Fluorine

dark grey or purple solid

red-brown liquid

yellow-green gas

pale yellow gas

The halogens

They exist as diatomic molecules. They have similar chemical properties. They react by gaining one valence electron to form anions.

Refer to CSEC Chemistry by Naresh Birju page 57 or CSEC Chemistry by Anne Tindale page 27

VIDEO

REACTIVITY OF THE HALOGENS

Unlike group 1 metals, the reactivity of the group 7 elements DECREASES DOWN THE GROUP or you can say INCREASES UP THE GROUP, so the smallest halogen, fluorine is the most reactive. The trend is this way because the halogens react by GAINING an electron and it is easier for a SMALLER ATOM TO GAIN AN ELECTRON readily than a larger one. Click here

VIDEO

DISPLACEMENT REACTIONS

A more reactive element will displace a less reactive element from its compound. This type of reaction also happens with the halogens Chlorine will displace bromine and iodine from bromide and iodide compounds respectively and bromine can only displace iodine from iodide compounds. Iodine cannot displace any of the other halogens as it is the least reactive of all.

GALLERY

07

The halogens

The strength of oxidizing powers of the elements is determined by how easily ONE SUBSTANCE TAKES ELCTRONS FROM ANOTHER SUBSTANCE. The group 7 elements react by GAINING ELECTRONS and those electrons THEY TAKE FROM ANOTHER SUBSTANCE. So in the same way fluorine is the smallest atom and is the most reactive (it can gain electrons the easiest), it also has the strongest oxidizing ability and will therefore TAKE THE ELECTRONS FROM ANOTHER SUBSTANCE so that it (the fluorine atom) can get it.

Oxidizing properties of the Group 7 elements: the halogens decrease down the group. Oxidizing ability or power is the ability of one substance to take electrons from another substance. The oxidising properties are essentially how the Group 7 elements react. Click here to go back to the page on how reactivity decreases down the group

Period 3

Trends in period 3

Elements change from metallic to nonmetallic. Atomic radius decreases. Electrical conductivity decreases. Click hereRefer to page 59-60 of CSEC Chemistry by Naresh Birju or page 28 in Concise Chemistry by Anne Tindale for further trends and details

THANK YOU!

Remember the three important points determining reactivity/ease of ionisation 1. Atomic radii (size of atom) 2. The attractive pull of the positive nucleus on the valence electrons 3. Electrons easily lost or gained. For Group 7: reactivity decreases down the group because the atomic radii increases, the attractive pull of the positive nucleus on the valence electron decreases so electrons are NOT EASILY GAINED