✟ 神秘の科学城 ✟: 七月 2014

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 ElementNoble 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.







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』




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