4.5 elements in Group 17

group 17 consists of elements of …

• F, fluorine

• Cl, chlorine

• Br, bromine

• I, iodine

• At, astatine

• Ts, tennessine

mnemonic …

first class biriyani in austria

• f, cl, br, i, at, ts

elements in group 17 are known as …

halogens (exist as diatomic molecules)

physical properties of group 17 elements …

• very low melting and boiling points

• does not conduct electricity or heat

• have pungent smell and are poisonous

• low density

• exist as diatomic molecules at low temperatures (F₂, Cl₂, Br₂, I₂, At₂, Ts₂)

why is the boiling point of group 17 elements low ?

the presence of very weak attraction force between particles (Van der Waals force). thus, only a small amount of heat is required to overcome the attraction force to separate halogen molecules.

the physical state of halogens at room temperature changes gradually…

from gas (fluorine, chlorine) → to liquid (bromine) → to solid (iodine, astatine)

going down the group …

1. the atomic radius or atomic size of elements increase

   • ^^ due to the number of electrons and electron filled shells increasing

2. the melting and boiling points increase

   • when going down the group, the atomic radius or atomic size increases

   • the attraction force between molecules also increases

   • more heat energy is need to overcome the attraction force between molecules

3. the density of elements increase

   • increase in atomic mass is higher than increase of atomic radius

4. the existence of different physical states of elements at different room conditions

   • atomic size increases down the group, so does the force of attraction

5. the electronegativity of halogens decrease

   • the tendency to accept electrons to form negative ions decrease.

physical state of: chlorine gas at room temperature

• molecular size of chlorine is small

• therefore, the force of attraction between molecules is weak

• this causes chlorine to exist as a greenish yellow gas at room temperature

physical state of: liquid bromine at room temperature

• the molecular size of bromine is larger than chlorine

• therefore, the force of attraction between molecules is stronger

• this causes bromine to exist as a reddish brown liquid at room temperature

physical state of: solid iodine at room temperature

• the molecular size of iodine is huge

• therefore, the force of attraction between molecules is very strong

• this causes iodine to exist as a purplish black solid

all halogens have …

7 valence electrons.

in chemical reactions, these atoms receive one electron and form ions with a -1 charge.

X + e^- → X^-

halogen elements such as chlorine, bromine and iodine exhibit …

the same chemical properties when reacting with …

• water to produce two types of acids

• iron to produce iron (III) halide

• sodium hydroxide solution to produce sodium salt and water

chlorine, bromine and iodine have the same … but different …

• chemical properties

• reactivity

the reactivity of the reaction between halogens and water…

decrease when going down group 17

Cl₂ Br₂ I₂

———————>

reactivity decreases

halogens react with water to form …

an acidic solution

reaction of chlorine with water

chlorine dissolves in water to form a mixture of hydrochloric acid and hypochlorous acid (bleaching agent). the light yellow solution is called chlorine water (chlorine solution)

Cl₂ (g) + H₂O (l) <—> HCl (aq) + HOCl (aq)

reaction of bromine with water

bromine dissolves in water to form a mixture of hydrobromic acid and hypobromous acid. the reddish brown solution is called bromine water (bromine solution)

Br₂ (l) + H₂O (l) <—> HBr (aq) + HOBr (aq)

bromine water is also a bleaching agent but is less effective than chlorine water.

reaction of iodine with water

iodine does not dissolve easily in cold water. it only dissolves slightly in hot water to produce a mixture of hydroiodic acid and hypoiodous acid. the resulting brownish yellow solution is called iodine water.

I₂ (s) + H₂O (l) <—> HI (aq) + HOI (aq)

halogens react with metal to form …

a metal halide.

• halogens are very electronegative elements and tend to combine with other metals to form metal halides. all halogens show similar chemical properties in their reaction with iron.

reaction of chlorine with metal

chlorine gas reacts vigorously with iron to produce a brown solid of iron (III) chloride

2Fe (s) + 3Cl₂ (g) —> 2FeCl₃ (s)

sodium hydroxide solution is used to absorb excess chlorine gas.

reaction of bromine with metal

bromine vapour reacts with iron to produce a brown solid of iron (III) bromide

2Fe (s) + 3Br₂ (g) —> 2FeBr₃ (s)

sodium hydroxide solution is used to absorb excess bromine gas.

reaction of iodine with metal

iodine vapour reacts with iron to produce a brown solide of iron (III) iodide.

2Fe (s) + 3I₂ (g) —> 2FeI₃ (s)

when halogens react with an alkaline solution ,

a metal halide, a metal halate and water will be produced.

reaction of chlorine with sodium hydroxide solution

chlorine reacts vigorously with sodium hydroxide solution to produce sodium chloride solution, sodium hypochlorite (sodium chlorate (I)) solution and water.

Cl₂ (g) + 2NaOH (aq) —> NaCl (aq) + NaOCl (aq) + H₂O (l)

reaction of bromine with sodium hydroxide solution

bromine reacts less vigorously with sodium hydroxide solution to produce sodium bromide solution, sodium hypobromite (sodium bromate (I)) solution and water.

Br₂ (l) + 2NaOH (aq) —> NaBr (aq) + NaOBr (aq) + H₂O (l)

reaction of iodine with sodium hydroxide solution

iodine reacts slowly with sodium hydroxide solution to produce sodium iodide solution, sodium hypoiodite (sodium iodate(I)) solution and water.

l₂ (s) + 2NaOH (aq) —> Nal (aq) + NaCl (aq) + H₂O (l)

elements in group 17 have the same ….

chemical properties because they have the same number of valence electrons, which is 7.

during a chemical reaction …

these atoms accept one electron into the valence shell to achieve a stable octet arrangement. this reaction forms a negative ion, such as F, Cl, Br, I, At with a -1 charge.

draw a chlorine atom receiving an electron to achieve stability

…

explain the reactivity of halogens

the reactivity of halogens decreases down the group.

• when going down the group, atomic size increases

• the distance of the valence shell becomes further away from the nucleus

• the force of attraction of the nucleus on the electrons in the valence shell become weaker

• the tendency for atoms to accept one electron to achieve a stable octet electron arrangement decreases.

compare the reactivity of fluorine and chlorine.

• chlorine atomic size is larger than fluorine atom.

• the distance between the nucleus and the valence electrons of chlorine atom is larger

• the force of attraction between the nucleus and the valence electrons becomes weaker for the chlorine atom,

• thus, the tendency of chlorine atom to accept a valence electron is lower than that of fluorine atom.

  F + e^- —> F^- (easier to happen)

  Cl + e^- —> Cl^- (more difficult to happen)

reactivity of astatine

astatine is under iodine in group 17 . thus, it is expected to react with water, iron and sodium hydroxide solution in the same way as iodine but slower (less reactive) than iodine.

astatine is a rare radioactive element because it is not chemically stable.