group18-1-17

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Arrangement of Elements in The

Periodic Table

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Question 1 :

The Melting Point and Boiling

Point increases down the Group18. Why?

Atomic size increases Forces of attraction between atoms

become stronger 

More heat energy is needed

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Question 2 :

The Melting Point and Boiling

Point of Group 18 elements are

very low (negative) generally.

Why?

Van der Waals force between atoms

are weak

Less heat energy is needed to

overcome the force

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Question 3 :

All elements in Group 18 are said

to be not reactive (Inert). Why?

The valence shells are fully filled with

8 electrons (except He)

Achieve octet (duplet) electron

arrangement

Not tend to release, receive or shareelectrons with other elements.

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Question 4 :

Density of Group 18 elements

increases down the group. Why?

The increase rate of atomic massis higher than the rate of atomic

size.

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The Inert nature of Group 18

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Group 1 – Alkali Metals

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Question 1 :

The Melting Point and Boiling

Point decreases down Group 1.Why?

Atomic size increasesMetallic bond between atoms become

weaker 

Less heat energy is needed

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Question 2 :Define “electropositivity”. 

The tendency of one atom todonate its valence electrons

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Question 3 :

The reactivity of alkali metalsincreases down the group.

Why?

Atomic size increasesDistance of valence e from nucleus is

further  

Attraction between nucleus and

valence e is weaker 

Easier to donate the single valence e

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Question 4 :

Potassium is more reactivethan sodium. Why?

Atomic size of K is bigger Distance of valence e from nucleus of  

K is further 

Attraction between nucleus andvalence e of  K is weaker 

Easier for K to donate the singlevalence e

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Question 5 :

Alkali metals conduct

electricity in solid phase.

Why?

Atoms contain free movingelectrons

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Summary

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Guestion 6:

 Alkali metals are stored in pariffinoils. Why?

The metals are very reactiveTo prevent them from being

oxidized by oxygen and wet

air 

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Chemical Properties

Alkali metals1) Reaction with water 

2) Reaction with oxygen

3) Reaction with chlorine gas

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Reaction with water 

2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g) 

2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) 

2K(s) + 2H2O(l) 2KOH(aq) + H2(g) 

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Observations

Reaction with water - Lithium

2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g)

• floats and move rapidly and randomly• Hissing sound (fizzing)

• Dissolved into water 

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Observations

Reaction with water - Sodium

2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

• turns into sphere• floats and move faster 

• small yellow flame 

• Hissing sound (fizzing)• Dissolved into water 

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Observations

Reaction with water - Potassium

2K(s) + 2H2O(l) 2KOH(aq) + H2(g)

•

turns into sphere• floats and move very fast

• burns in lilac flame

• Hissing sound (fizzing)

• Dissolved into water 

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Gas test : burning splinter 

  Hydrogen gas:

Collect the gas into a test tubeApproach the burning splinter towards the

mouth of test tube

“pop” sound occurred 

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alkali test : Red litmus

 Alkali aka LiOH, NaOH, KOH :

Put some solution onto a glass discDip the red litmus into the liquid

It turns blue

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Reaction with oxygen

2Li(s) + O2(g) 2Li2O(s)

2Na(s) + O2(g) 2Na2O(s)

2K(s) + O2(g) 2K 2O(s)

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Observation

Lithium + oxygen

Burn in red red flame

White solid (lithium oxide)

Li2O dissolves in water 

2Li(s) + O2(g) 2Li2O(s)

Li2O(s) + H2O(l) 2LiOH(aq)

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Observation

Sodium + oxygen

Burn brighter in red yellow flame

White solid (sodium oxide)

Na2O dissolves in water 

2Na(s) + O2(g) 2Na2O(s)

Na2O(s) + H2O(l) 2NaOH(aq)

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Observation

Potassium + oxygen

Burn in red lilac flame

White solid (potassium oxide)

K2O dissolves in water 

2K(s) + O2(g) 2K 2O(s)

K2O(s) + H2O(l) 2KOH(aq)

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Reaction with chlorine

2Li(s) + Cl2(g) 2LiCl(s)

2Na(s) + Cl2(g) 2NaCl(s) 

2K(s) + Cl2(g) 2KCl(s)

The salts produced here are soluble in water 

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Group 17 - Halogen

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Group 17

HalogenHalogen

In CCl4 

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THE DANGERS OF HALOGENS

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Physical Properties Of Halogens

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Physical Properties of Halogens

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Summary

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Physical Properties Of Group 17

4.94Grey solid184114Iodine

3.14Brownish

Liquid

59-7Bromine

0.003Pale

Green gas

-35-101Chlorine

0.0016Pale yellow

gas

-188-220Fluorine

Density/

G dm-3 

Appearance

Boiling

Point/ oC

MeltingPoint / oC

Element

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Summary of Physical Properties

Physical state : gas liquid solid

Low melting and boiling point

Do not conduct electricity

Poor heat conductor 

Low density

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Question 1 :

The Melting Point and Boiling

Point increases down Group 17.Why?

Molecular size increases

Forces of attraction between

molecules become stronger 

More heat energy is needed

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Question 2 :

Halogens do not conduct

electricity . Why?

The particles of halogens are

molecules

They have no free ions

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Chemical Properties

Halogens1) Reaction with water 

2) Reaction with Iron

3) Reaction with alkali 

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Observations

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1) Reaction with water 

I2(g) + 2H2O(l) HI(aq) + HOI(aq) 

Br2(g) + 2H2O(l) HBr(aq) + HOBr(aq) 

Cl2(g) + 2H2O(l) HCl(aq) + HOCl(aq) 

Name : HOCl = hypochlorus acidHOBr = hypobromus acid

HOI = hypoiodus acid

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2) Reaction with iron 

2Fe(s) + 3Cl2(g) 2FeCl3(s) 

Name : FeCl3 = Iron(III) chlorideAll the salts produced are soluable in

water 

2Fe(s) + 3Br2(g) 2FeBr3(s) 2Fe(s) + 3I2(g) 2FeI3(s) 

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How to draw the diagram of Iron

being burned in halogens

Heating

Potassium permangate + HCl

Chlorine gas

Iron wool

Soda chalk

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How to draw the diagram of Iron

being burned in halogens

HeatingHeating

Brominegas

Heating

Bromine water 

Iron wool

Heating

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3) Reaction with alkali

NaOH(aq)+Cl2(g) NaCl(aq)+NaOCl(aq)+H2O(l) 

Name : NaOCl = sodium chlorate(I)NaOBr = sodium bromate(I)

NaOI = sodium iodate(I)

NaOH(aq)+Br2(g) NaBr(aq)+NaOBr(aq) + H

2O(l) 

NaOH(aq)+I2(g) NaI(aq)+NaOI(aq)+ H2O(l) 

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Summary 1

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Summary 2

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Question 3 :

The reactivity (electronegativity)

of halogens decreases down the

group. Why?

Atomic size increasesDistance of valence e from nucleus is

further  

The strength to attract one electron

into valence shell is weaker 

Harder to attract electron

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Question 4 :

Define “electropositivity”. 

The tendency of one atom toattract electrons into the

outermost occupied shell

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