JOM KIMIA A1

PERIODIC TABLE OF ELEMENTS

D. GROUP 17 ELEMENTS

http://periodictable.com/

1. The group 17 elements are:

Flourine 2.7

Chlorine 2.8.7

Bromine 2.8.18.7

Iodine 2.8.18.18.7

Astatine 2.8.18.32.18.7

2. Group 17 elements are known as halogens

3. Halogens exist as diatomic molecules.

4. Halogens have seven valence electrons.

GROUP 17

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Physical Properties of Group 17 Elements

1. All Group 17 elements are non-metals .

Element SymbolProton

Number

Physical state at room

temperature

ColourMelting point

Boiling point

Flourine F 9 Gas Pale yellow

IncreaseIncrease

Chlorine Cl 17 GasGreenish-

yellow

Bromine Br 35 LiquidReddish-

brown

Iodine I 53 SolidPurplish-

black

2. Halogen have low melting and boiling points because their molecules are attracted to each other by weak forces. Less energy is needed to overcome the forces .

3. When going down the group, the melting and boiling points increases. This is because the molecular size increases.

Diagram:

Cl2

Cl2

Cl2

Cl2

van der Waals forces

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Chemical Properties of Group 17 Elements

1. Group 17 elements react with water, metal and alkali.

a) Halogen react with water to form 2 acids

In general:

X2 + H2O HX + HOX ; X is halogen

HX and HOX solutions are acidic. HOX solution exhibits bleaching properties.

Example:

Cl2 + H2O HCl + HOClChlorine Water Hydrochloric Hypochlorus acid acid

Br2 + H2O HBr + HOBrBromine Water Hydrobromic Hypobromus acid acid

I2 + H2O HI + HOIIodine Water Hydrobromic Hypoiodus acid acid

What is physical state of astatine?

Practical book Carry out an experiment 4.2 page 39

HW: Draw diagram and answer the question

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b) Halogens in gaseous state react with hot iron

To form a brown solid , iron(III) halides.

In general:

2Fe + 3X2 2FeX3 ; X is halogen

Example :

2Fe + 3Br2 2FeBr3

Iron Bromine Iron(III) bromide

2Fe + 3Cl2 2FeCl3

Iron Chlorine Iron(III) chloride

2Fe + 3I2 2FeI3

Iron Iodine Iron(III) iodide

c) Halogens react with sodium hydroxide solution , NaOH.

To form sodium halide, sodium halate and water

The halogens are decolourised during these reaction.

In general:X2 + NaOH NaX + NaOX + H2O

[X is halogen]

Example:

2 NaOH + I2 NaI + NaOI + H2O

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Chemical Properties of Group 17 Elements

Fluorine is the most electronegative element

Elelctronegativity of an element refers to the measurement of the strength of an atom in its molecule to attract electrons towards its nucleus.

WHY they have similar chemical properties???

Halogens have 7 valence electrons.

When halogens take part in chemical reactions, their atom always gain one electron to achieve a stable octet electron arrangement.

The explanation …… a) The atomic size increases down the group.

b) The distance of the outermost shell becomes further from the nucleus .

c) The force of attraction of the nucleus on the electrons of the outermost shell decrease.

d) The tendency of an atom to receive one electron to achieve an octet electron arrangement decrease

Chlorine, Bromine and Iodine have similar chemical properties but differ in reactivity.

The Reactivity of Halogens decrease down the group.Do You Know WHY???

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Safety Precautions in handling Group 17 elements

1. The vapour of Flourine, Chlorine and Bromine are poisonous.

2. The following precaution should be taken when handling halogen:

a) Halogen gas and liquid should be handled inside a fume chamber

b) Wear safety goggles when handling halogen fumes.

c) Wear safety gloves when handling halogen materials.

Do It Yourself

Element X Y ZProton number 9 17 35

1. Elements X, Y and Z are same group in the periodic table.

a. What is the valence electron of the elements X,Y and Z?

seven(7)

b. Which group in the periodic table can you find the elements X,Y and Z?

group 17

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c. Element Y can react with water. What are the properties of the solution produced?

Acidic and bleaching properties

d. Write an equation for the reaction between element Z and hot iron.

2Fe + 3Z2 2FeZ 3

3. List all halogen elements from the top to the bottom of group 17.

Flourine, Chlorine, Bromine, Iodine and Astatine

4. Which are the most reactive and least reactive halogen?

Most reactive: Flourine least reactive : Astatine

4. Write the chemical equations for the following reaction: a) Chlorine with water

Cl2 + H2O HCl + HOCl

b) bromine with iron

2 Fe + 3Br2 2FeBr 3

c) iodine with sodium hydroxide

2 NaOH + I2 NaI + NaOI + H 2O

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5. Explain the changes to the reactivity of halogens when going down group 17.

The atomic size of halogen increases down the group.

The distance of the outermost shell becomes further from the nucleus. Therefore, the force of attraction of the nucleus on the electrons of the outermost shell decrease.

The tendency of an atom to receive one electron to achieve an octet electron arrangement decrease. This causes the reactivity to decrease down the group .

Kamal. A.http://kemhawk.webs.com