Group 7 elements chemistry

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Chemistry

Group VII - Halogens

The halogens are the elements found in group VII of the p-block on the periodic table. They all

contain 7 electrons in their outermost shell and gain one electron to form a negatively charged

ion. The four first elements are fluorine, chlorine, bromine and iodine. They are diatomic,

meaning they exist as F

, Cl

, Br

and I

Property

Fluorine, F

Chlorine, Cl

Bromine, Br

Iodine, I

State at room

temperature

gas

liquid

solid

Color

Pale yellow

Yellow green

Red-brown

Grey (when solid)

Brown (when liquid)

Purple (when vapor)

Melting point/°C

-220

-101

-7

114

Atomic Radius/nm

0.072

0.099

0.114

0.133

As we go down group VII, the number of electrons and fully filled shell increases. Hence atomic

radius increases down the group. With increase in electrons, there is an increase in van der

Waals forces between molecules. More van der Waals forces require more energy to break.

Hence, melting point increases down the group and substances change state from gas to liquid

to solid. The color of the halogen molecules at room temperature gets darker as we go down

the group. This is because of the complementary color of the light they absorb from the visible

region of the electromagnetic spectrum. The color of the molecules depends on the amount of

energy the outer electrons absorb.

Reactivity of halogens

Halogens become less reactive down group 7. A more reactive halogen can displace a less

reactive halogen from an aqueous halide solution. Halogens react by gaining one electron in

their outermost shell to form an octet. As you go down group 7 a fully filled shell is being

added, increasing atomic radius and decreasing the pull from the nucleus. As a result, the

elements cannot attract electrons to itself as easily and reactivity decreases.

Halogen

Halide Ions

Chloride Cl

(aq)

Bromide Br

(aq)

Iodide I

(aq)

Turns orange

Turns brown

No reaction (Br

cannot displace Cl)

Turns from orange to

brown

No reaction (I cannot

displace Cl)

No reaction (I cannot

displace Br)

The reactions can be confirmed by adding cyclohexane to the solution. The cyclohexane layer

dissolves the halogen only, so any color changes can be confirmed.

Oxidizing and Reducing Agents

The E° value can tell whether a substance is a good oxidizing or reducing agent. The more

positive the E° value, the better it is as an oxidizing agent, gaining electrons. The more negative

the E° value, the better it is as a reducing agent, releasing electrons. As you go down group 7

oxidizing ability decreases as the E° value decreases, but reducing ability increases. Fluorine is

the best oxidizing agent in group 7.

Reaction of halogens with water

Fluorine and chlorine are able to oxidize water while bromine and iodine cannot. Fluorine is

such a strong oxidizing agent that it is able to oxidize water to oxygen.

+ 2H

O --> 4HF + O

Chlorine reacts slowly with water to form hydrochloric acid and chloric (I) and (HClO).

+ H

O --> HCl + HClO

Reaction of halogens with alkali

Chlorine, Bromine and iodine undergo similar reactions with alkalis. The products depend on

the temperature at which the reaction is carried out.

-With Cold dilute NaOH- sodium chlorate (I) is formed

2(g)

+ 2NaOH

(aq)

--> NaCl

(aq)

+ NaClO

(aq)

+ H

(l)

In this reaction, the chlorine molecule is simultaneously oxidized and reduced. This is called a

disproportionation reaction.

-With Hot concentrated NaOH- sodium chlorate (V) is formed

3Cl

2(g)

+ 6NaOH

(aq)

--> 5NaCl

(aq)

+ NaClO

3(aq)

+ 3H

(l)

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Khan Academy Chemistry Group VII - Halogens The halogens are the elements found in group VII of the p-block on the periodic table. They all contain 7 electrons in their outermost shell and gain one electron to form a negatively charged ion. The four first elements are fluorine, chlorine, bromine and iodine. They are diatomic, meaning they exist as F2, Cl2, Br2 and I2. Property State at room temperature Color Fluorine, F2 gas Chlorine, Cl2 gas Bromine, Br2 liquid Iodine, I2 solid Pale yellow Yellow green Red-brown Melting point/°C Atomic Radius/nm -220 0.072 -101 0.099 -7 0.114 Grey (when solid) Brown (when liquid) Purple (when vapor) 114 0.133 As we go down group VII, the number of electrons and fully filled shell increases. Hence atomic radius increases down the group. With increase in electrons, there is an increase in van der Waals forces between molecules. More van der Waals forces require more energy to break. Hence, melting point increases down the group and substances change state from gas to liquid to solid. The color of the halogen molecules at room temperature gets darker as we go down the group. This is because of the complementary color of the light they ...
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