SPM Form 4 Chemistry Notes — Chapter 4『4.2』Group 18 Elements

4.2 Group 18 Elements

● Known as noble gases（inert gases）due to their non-reactive behavior.『G18 的element是惰性气体，不会发生reaction』

● This group consist of six elements，namely Helium，Neon，Argon，Krypton，Xenon and Radon

● Have 8 valence electron expect helium（has 2 valence electron）『注：He被放在G18那是因为它也是Noble gases（Have stable duplet electron arrangement）』

● The form 1% of air，and most of this is argon.

Physical Properties

● Atomic size is small but increases down the group.

● Density - Low but increases down the group.

Atomic Size

● The atomic size increases when down the group.

● It is because the number of electron occupied shells in the atom increases from helium to radon.『因为electron增加，所以大小也增加』

Melting Point & Boiling Point

● The melting and boiling point of noble gases are very low.

● This is because all noble gases exist as monoatoms（Means 1 molecule contain 1 atom）.The force in between all these atoms is the weak van der Waals' Force.

● Therefore very little energy is needed to overcome this force during melting and boiling.

『G18 element是monoatoms，所以atoms 之间的van der Waals' Force 很弱，所以只需要一点点的热量就可以让它们达到熔点与沸点』

Changes Down the Group

● The melting and boiling point increase down the group.

● The atomic size increases down the group.

● The intermolecular force increases.

● More energy is needed to overcome the stronger forces，hence the melting and boiling point increase.

Density

● The density of noble gases are very low but increases steadily down the group.

Density = Mass / Volume

● 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.『质量和体积都会增加，可是质量增加比体积还快』

Chemical Properties

● All the noble gases are inert / chemically non-reactive elements.

● This is because their outermost shell is full of electrons （8 valence electrons or 2 valence electrons for Helium）

● These octet / duplet electron arrangement are very stable.The atoms do not receive，donate or share electron with others.

● So，noble gases exist as monoatomic gases.

Uses of the G18 Element（Noble Gases）

1. Helium

● Airship  and weather balloons - because it doesn't burn in air UNLIKE hydrogen which with "flammable" consequences.『因为Helium是inert gases，不像Hydrogen那么reactive』

2. Neon

● It is used in advertising signs and fluorescent lights.

● Used in landing light bulbs for planes.

3. Argon

● It used in filament bulbs because the metal filament will not burn in Argon and it reduces evaporation of the metal filament.

● Fire Extinguisher

4. Krypton

● Used in fluorescent bulbs，flash bulbs and laser bulbs.

● Used in lasers to repair retina of eye.

5. Xenon

● Making electron tube & stroboscopic lamps.

● Used in fluorescent bulbs，flash bulbs and lasers.

6. Radon

● Treatment of cancer.

● To detect pipe leakage.

温馨小提示：

1. Force of attraction的分类：

     - Metallic Bond『Metal atom- Valence electron between nucleus』

     - Van der Waals' Force = Intermolecular Force『Non-metal - between molecules』

     - Electrostatic Force 『Ionic Bond - between Metal and Non-metal』

2. Electron Arrangement

     - Stable duplet『For Hydrogen ion and Helium molecule which only have 2 valence electron』

     - Stable octet『For ion or molecule which have 8 valence electron』