Group 17 Elements - Halogens

1. Group 17 elements are typical non-metals and also known as halogens.
2. The elements in this group are fluorine. chlorine, bromine, iodine and astatine.
3. In nature, all halogens exist as diatomic molecules. They are written as F₂, Cl₂, Br₂, I₂ and As₂.
4. Most of the halogens exist in the nature as halide salts.
5. Halide is the name given to the ion of halogens. Table below shows the corresponding halide of the halogen.

Halogen	Halide
Fluorine	Fluoride
Chlorine	CHloride
Bromine	Bromide
Iodine	Iodide

Physical Properties of Halogens

1. All group 17 elements are non-metals. Therefore they are heat and electricity insulator.
2. Table below shows the electron arrangement and physical properties of group 17 elements.

Name	Proton Number	Electron arrangement	Colour	Melting point	Boiling point
Fluorine	9	2.7	pale yellow gas	-220ºC	-188ºC
Chlorine	17	2.8.7	Yellowish green gas	-102ºC	-34ºC
Bromine	35	2.8.18.7	dark red liquid, brown vapour	-7ºC	59ºC
Iodine	53	2.8.18.18.7	black solid, purple vapour	114ºC	184ºC
Astatine	85	2.8.18.32.18.7	black solid, dark vapour	302ºC	380ºC

Size of Atom and Density

1. The atomic size of group 17 elements increases down the group.
2. This is due to the increase of number of electron shell down the group.
3. The density of group 17 elements is also increases down the group.
4. This is because the rate of increment of the atomic mass is higher than the rate of increment of the volume.

Melting Point and Boiling Point

1. As shown in the graph to the right, the melting points and boiling increase steadily down the group.
2. The physical state at room temperature also change from gas to liquid and then to solid.
3. This is because the intermolecular attractive force (van der Waals force) increase with increasing size of atom or molecule.