Wednesday, 7 January 2015

4.4 Group 17 Elements

Physical properties
■ Elements of Group 17 also known as halogens

Flourine, F
Chlorine, Cl
Bromine, Br
Iodine, I
Astatine, At

The following mnemonic method can be used to memorize the sequence of elements in Group 17.
Fairy Clowns Broil Innocent Ants.
■ Physical properties of halogens

Elements Proton number Atomic radius (nm) Melting point (℃) Boiling point (℃) Density (gcm-3) Color
Flourine, Fl 9 0.06 -220 -187 1.12 Light yellow
Chlorine, Cl 17 0.10 -102 -34 1.57 Greenish yellow
Bromine, Br 35 0.12 -7.2 59 3.13 Reddish-brown
Iodine, I 53 0.14 114 183 4.95 Purple-black

Low melting points and boiling point.
All halogens exist as diatomic molecules gas (F2, Cl2, Br2, I2, At2)

Do not conduct electricity

Weak conductors of heat

Low density

The animation below shows the changes in physical properties of Group 17 elements down the group.

Chemical properties
■ Arrangement of electron in halogen elements.

Element Electron configuration Arrangement of electron
Flourine 2.7
Chlorine 2.8.7
■ Chemical reaction.

Alkali halogens elements show similar properties when reacting with certain compounds.
Halogens react with water to form two acid.
Laboratory Activity 4.4.1: Studying the reaction of chlorine, bromine and iodine with water
Halogens react with hot iron to form a brown solid, iron (II) halides.
Laboratory Activity 4.4.2: Studying the reaction of halogens with iron wool
Halogens react with sodium hydroxide solution to form sodium halide, sodium halate (I) and water.
Laboratory Activity 4.4.3: Studying the reaction of halogens with aqueous sodium hydroxide solution

Brief explanation on the reaction of halogen.
All halogens have 7 valence electron.
They receive an electron to form an anion or negative ion in order to attain the stable octet or noble gas electron arrangement.

The reactivity of halogens decreases as down the group.

The animation below shows the explanation on the changes on the reactivity of alkali metals.

■ This video contains information about the physical properties and the reactions of the Group 17 elements.

⇲ For exercise(objective and subjective), download for free on Android OS.

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