PERIODIC TABLE OF ELEMENTS Group 18 4S1 Monday, 15/4/2011 10.45 – 11.55 am

Members of Noble Gases Helium Neon Argon Krypton Xenon Radon

Atomic radius increases going down the group - Low mp & bp Physical Properties Atomic radius increases going down the group - Low mp & bp - Mp & bp increases down the group Low density Colourless gases Insoluble in water Cannot conduct electricity Poor conductors of heat

Physical Properties - increases down the group - bcoz number of shells Atomic radius (atomic size) - increases down the group - bcoz number of shells occupied with electrons increases down the group

2. Low mp & bp - bcoz noble gases are made up of single atoms (monoatomic) - the atoms are held together by weak van der Waals force of attraction - only small amount of E is needed to overcome the forces of attraction during melting & boiling

3. Mp & bp increases down the group - bcoz atomic size increases down the group. - thus, van der Waals forces of attraction btwn atoms of noble gases become stronger - more E is needed to overcome the stronger forces of attraction during melting & boiling

4. Low density - however, density increases slowly down the group - bcoz increase in mass is bigger compared to increase in volume when going down the group

Unreactive properties of noble gases Element Electron arrangement Helium 2 Neon 2.8 Argon 2.8.8 Krypton 2.8.18.8 Xenon 2.8.18.18.8 Radon 2.8.18.32.18.8 Duplet arrangement Octet arrangement

(Cont.) Unreactive properties of noble gases due to duplet & octet arrangement, noble gases are very stable do not release e-, accept or share e- among each other or with other atoms noble gases exist as monoatoms Noble gases are chemically inert or chemically unreactive

Uses of Group 18 elements Helium - fill weather balloons & airships - mixture of 80% He & 20% O2 is used by divers as artificial atm (bcoz He is less soluble in the blood compared to N2  can cause decompression sickness = bends) - used in thermometer to measure very low temp.

Airship

2. Neon - fill advertising light bulbs, colour: reddish- orange - used as indicator light in small neon lamp  indicate circuit is on

3. Argon - fill electric bulbs - supply inert atm for welding at high temp. - carrier gas in liquid-gas chromatography

Liquid-gas chromatography

4. Krypton - fill high speed photographic flash lamps - in lasers to repair retina of the eye

4. Xenon - used in electron tubes & spectroscopic lamps - used in bubble chambers 5. Radon - used in the treatment of cancer bcoz it is radioactive

Electron tubes