Group 18 Elements – Noble Gases

  1. The “Noble Gases” are the last group in the Periodic Table, they also known as “inert gas”, due to their non-reactive behavior.
  2. This group consist of six elements, namely Helium, Neon, Argon, Kripton, Xenon and Radon.
  3. They are non-metallic, colourless gases at room temperature and pressure with very low melting points and boiling points.
  4. They form 1% of air, and most of this is argon.
  5. The size of atom increases down the group, due to the increase number of electron shell.
NameProton numberElectron arrangementMelting pointBoiling point
Helium22-270°C-269°C
Neon102.8-249°C-246°C
Argon182.8.8-189°C-186°C
Krypton362.8.18.8-157°C-152°C
Xenon542.8.18.18.8-112°C-108°C
Radon862.8.18.32.18.8-71°C-62°C

Physical Properties

Solubility and Conductivity

  1. All noble gas are insoluble in water.
  2. They are not conductor of heat and electricity.

Melting Point and Boiling Point

  1. As show in the table above, the melting and boiling point of noble gases are very low.
  2. This is because all noble gases exist as monoatoms. The force in between all these atoms is the weak van de Waals’ Force.
  3. Therefore very little energy is needed to overcome this force during melting and boiling.

Density

  1. The density of noble gases are very low.
  2. Nevertheless, the density increases steadily down the group.
  3. Density of a substance is given by the equation “Density=Mass/Volume”.
  4. Down the group, both the mass and the volume increase, but increase of mass is faster than the volume, hence the density increases down the group.

Chemical Properties

  1. All the noble gases are non-reactive elements.
  2. This is because their valence shell is full of electrons.
  3. In the chemical world, an atom is in the chemically most stable state if their valence shell is full with eight electrons (or 2 electrons for the first shell.).
  4. Therefore all noble gases do not react with other elements, due to their stable electronic structure.
  5. They exist as single atoms, that is they are monatomic.

Uses of the Group 18 Elements

Helium

Airship

  1. The gas is much less dense than air. Therefore it is used in balloons and ‘airships’.
  2. Because of its inertness it doesn’t burn in air UNLIKE hydrogen which used to be used in large balloons with ‘flammable’ consequences.

Deep-sea Diving

  1. Helium is also used in gas mixtures for deep-sea divers.
  2. This is because the solubility of the helium is very low. Therefore it will not dissolve in the blood even though the pressure of the surrounding is very high.

(Neon Bulb)

Neon

  1. Neon emits light when high voltage electricity is passed through it.
  2. Because of this, it is used in glowing ‘neon’ advertising signs and fluorescent lights.
Argon
(Filament Bulb)

Filament Bulb

  1. Argon, like all the Noble Gases is chemically inert.
  2. It used in filament bulbs because the metal filament will not burn in Argon and it reduces evaporation of the metal filament.

(Welding)

Welding

Argon also used to produce an inert atmosphere in high temperature metallurgical processes, eg in welding where it reduces brittle oxide formation reducing the weld quality.

Fire Extinguisher

Argon is also used for extinguishing fires where damage to equipment is to be avoided

(Laser)

Krypton

Krypton is used in fluorescent bulbs, flash bulbs and laser beams.

Xenon

(Camera Flash)
(Fluorescent Bulb)

Also used in fluorescent bulbs, flash bulbs and lasers.

Radon

Used in radiotherapy to kill cancer cell.