ZON PENA

Introduction

Group-18:Noble Gas

• The "Noble Gases" are the last group in the Periodic Table, they also known as "inert gas", due to their non-reactive behavior.
• As shown in the diagram on the right, this group consist of six elements, namely Helium, Neon, Argon, Kripton, Xenon and Radon.
• They are non-metallic, colourless gases at room temperature and pressure with very low melting points and boiling points.
• They form 1% of air, and most of this is argon.

Physical Properties

• The table above shows the physical properties of the noble gas.
• The size of atom increases down the group, due to the increase number of electron shell.

Solubility an Conductivity

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

Melting Point and Boiling Point

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

Changes Down the Group

• The melting and boiling point increase down the group.
• This is because the size of the atom increases down the group.
• The strength of van de Waals force increases as the size of the particles (atoms) increases.
• More energy is needed to overcome the force in between the atoms during melting and boiling, hence the melting and boiling point become higher.

Density

• The density of noble gases are very low.
• Nevertheless, the density increases steadily down the group.
• Density of a substance is given by the equation .
• 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

• All the noble gases are non-reactive elements.
• This is because their valence shell is full of electrons.
• 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.).
• Therefore all noble gases do not react with other elements, due to their stable electronic structure. (We will discuss in more detail in the very next chapter, the Chemical Bond.)
• They exist as single atoms, that is they are monatomic.

All elements in Group 18 are very stable and do not react with themselves or other elements to form any molecule or compound. All elements in Group 18 exist as monoatoms.

Uses of the Group 18 (Noble Gases)

Helium

Airship The gas is much less dense than air. Therefore it is used in balloons and 'airships'. Because of its inertness it doesn't burn in air UNLIKE hydrogen which used to be used in large balloons with 'flammable' consequences.	Airship
Deep-sea Diving Helium is also used in gas mixtures for deep-sea divers. 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.	Deep-sea diving

Neon

Neon emits light when high voltage electricity is passed through it. Because of this, it is used in glowing 'neon' advertising signs and fluorescent lights.

Neon Tube

Argon

Filament Bulb Argon, like all the Noble Gases is chemically inert. It used in filament bulbs because the metal filament will not burn in Argon and it reduces evaporation of the metal filament.	filament bulb
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.	welding
Fire Extinguisher Argon is also used for extinguishing fires where damage to equipment is to be avoided
Argon bubbles are used to stir mixtures in steel production. Argon is the cheapest to produce.

Krypton

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

Fluorescent Bulb

Flash Bulb

Xenon

Also used in fluorescent bulbs, flash bulbs and lasers.

Radon

Almost no uses!