C2aL8 Halogens

Key Words

Astatine - a radioactive halogen.

Bromine - a dark brown toxic gas

Chlorine - a toxic green gas.

Fluorine - a very reactive yellow gas.

Group 7 - a family of reactive gases called the halogens.

Halide - a salt made between a metal and a halogen.

Halogens - the Group 7 gases.

Iodine - a dark crystalline solid that sublimes to make a purple gas.

Ionic compounds - compounds held together with ionic bonds.

Non-metal - elements that do not have metallic properties.

Salts - compounds formed by reactions between metals and non-metals.

Grade E

The halogens form a family at the right of the periodic table, the second column from the right.

They are also called the Group 7 gases.  They all have 7 outer shell electrons.  Halogen means that they form salt.

The family consists of:

• Fluorine (F) - a very reactive and highly poisonous gas;

• Chlorine (Cl) - a reactive and toxic green gas, often used to sterilise swimming pools;

• Bromine (Br) - a brown toxic liquid that readily changes to a gas;

• Iodine (I) - a grey crystalline solid that sublimates into a purple gas;

• Astatine (At)- a highly radioactive element.

All halogens exist as molecules of two atoms joined together by a covalent bond.

They all react readily with water to form acids.

With metals, Group 7 elements form salts.  The halide ions have a single (-1) negative charge.

Grade C

The reactions of Group 7 elements are similar:

Sodium + chlorine ® sodium chloride

Caesium + fluorine ® caesium fluoride

They all form negative ions with a single negative charge.

The alkali metals become less reactive as we go down the group:

• Fluorine is very reactive.  It can even react with the noble gases.

• Iodine is not very reactive.

Click on the link to see a demonstration of the reactions of Fluorine:

http://www.youtube.com/watch?v=mG6EG_igTGw

The reason for the way that fluorine is so reactive is that the 7 outer shell electrons are close to the nucleus.  Therefore the element wants to grab an extra electron to make the outer shell full, it more reactive.  This effect is less pronounced as we go down the group.

Grade A

There is a reactivity series within the halogens.  Chlorine will displace bromine from a bromide.

chlorine + potassium bromide ® potassium chloride + bromine