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

2. Members of Noble Gases
Helium
Neon
Argon
Krypton
Xenon
Radon

3. 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

4. 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

5. 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

6. 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

7. 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

8. Unreactive properties of noble gases
Element
Electron arrangement
Helium 2
Neon
2.8
Argon
2.8.8
Krypton
Xenon
Radon
Duplet arrangement
Octet arrangement

9. (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

10. 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.

11. Airship

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

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

14. Liquid-gas chromatography

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

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

17. Electron tubes