GROUP 18

Group 18

·         Group 18 elements are called noble gases

·         Elements= Helium, Neon, Argon, Krypton, Xenon, Radon

Physical properties:

·         Colourless gases at room temperature and pressure.

·         Low melting points and boiling points.

·         Low densities

·         Insoluble in water.

·         Do not conduct electricity

·         Poor conductors of heat

·         Exist as monoatomic gases at room condition

The physical properties of group 18 elements change down the group

a)      Atomic radius or atomic size increases.

Reason:

Number of occupied shells in the atom increases

b)      Melting point and boiling point increases.

Reason:

Forces of attraction between atoms become stronger as atomic size of elements increases.

c)       Density of elements increases

Reason:

Atomic mass increases more than the increase of atomic radius (volume of atom).

v  All group 18 elements are inert.

v  Inert means chemically unreactive.

v  Reason : All noble gases have the maximum number of valence electron on

outermost shell, which are two or eight valence electron.

v  Elements that has two valence electrons on the first shell is called duplet electron arrangement.

v  Elements that has eight valence electrons on the outermost shell is called octet electron arrangement.

The Uses of noble gases:

Helium	§  To fill airships and hot air balloons.
Neon	§  To fill neon lamps in signboards.
Argon	§  To fill an electric bulb.
Krypton	§  It is used in lasers to repair the retina of the eye. §  To fill the flash lights of cameras.