Group 17

Group 17 elements-known as halogen-exist as diatomic atom-non-metallic

Elements Symbol Proton Number

Electron Arrangement

No.of shells/orbital

Fluorine F2 9 2.7 2

Chlorine Cl2 17 2.8.7 3

Bromine Br2 35 2.8.18.7 4

Iodine I2 53 2.2.18.18.7 5

Physical propertiesdown the group

Colour

Pale yellow (g)

Greenish yellow (g)

Reddish brown (l)

Purplish-black (s)

F F

Cl Cl

Br Br

I I

F F

Cl Cl

Br Br

I I

Physical propertiesDOWN THE GROUP

increases

Molecules are attracted by van der waals ForceSize increase More Energy required to overcome these forces

Why the molecular size of halogens increase down the group?

Gas

Gas

liquid

solid

Molecular sizeMelting/boiling pointDensity

CHEMICAL PROPERTIESdown the group

Reactivity decrease down the group

• Atom size increase• Outermost shells become further

from nucleus• The strength to attract one

electron into the shell by nucleus weaker

• So,reactivity decrease

F F

Cl Cl

Br Br

I I

Chemical reactions

with water: form two acidsX2 + H2O ↔ HX +HOX

with NaOH: from sodium halide,sodium halite, dan waterX2 +2NaOH(aq) ↔ NaX (aq) + NaOX(aq) + H2O (l)

with iron: form a brown solid, iron (III) halides2Fe (s) + 3X2(g) → 2FeX3

Reaction of halogen wih water

Safety precautions

• Element E is placed below element D in group 17 of periodic table.

• a) Compare the melting point and boiling point of element D with element E. Explain your answer.

• • 2. Explain why • Iodine and bromine have similar chemical

properties.• Iodine is less reactive than bromine.

Conclusion