© Boardworks Ltd 2003 THE HALOGENS. © Boardworks Ltd 2003 Halogens and the Periodic Table These are the Halogens or Group 7 Elements H Li Na K Rb Cs Fr

© Boardworks Ltd 2003

THE HALOGENS


Halogens and the Periodic Table

These are the Halogens or Group 7 Elements

H

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg

V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa Kr

Y Zr Nb Mo Tc Ru Pd Ag Cd In Sn SbSr TeRh

Ba Hf Ta W Re Os Ir Au Hg Tl Pb Bi PoLa AtPt

Ra Rf Db Sg Bh Hs Mt ? ?Ac ?

Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

He

B C

As Br

At

Cl

F

I


Electronic Structure

All the Group 7 elements have 7 electrons in the outermost shell.

F

Cl

Br

I

At

Bromine

Iodine

Astatine

Fluorine 2,7

Chlorine

2,8,7

And so on


Halogen molecules

All the Group 7 elements are molecules containing two atoms. (They are diatomic)Each atom is 1 electron short of a noble gas electron structure.By sharing electrons in a covalent bond full outer electron shells are achieved.

F FF F


Patterns: colour

The group 7 elements get darker as you go down the group.

F

Cl

Br

I

Darker

Bromine solution.

Note the bromine vapour above the liquid

What colour would you expect astatine to be?


Patterns: physical state

Melting Points and boiling points increase as the molecules get bigger.

What is the physical state: solid, liquid or gas?

Element Size Melting Point (oC)

Boiling Point (oC)

Physical State

Fluorine -220 -188

Chlorine -101 -35

Bromine -7 59

Iodine +114 184

gas

gas

liquid

solid


Patterns: reactivity

Reactivity increases up the group.

F

Cl

Br

I

At Incr

easi

ng R

eact

ivity

For example, their reaction with hydrogen

F2Reacts instantly even at -200 C

Cl2 Reacts slowly in dark.Explodes in light

Br2Needs heating to +200 C in order to react

I2Does not react completely even at 500 C

How will Astatine react?


Reactivity and electron structures

Most halogen reactions involve gaining an electron.

1. The atoms get bigger as you go down the group. This reduces the attraction of the (+) nucleus for an additional (-) electron.

2. ‘Shielding’ by the inner electron shells also reduces the attraction from the nucleus.As we go down the group the tendency to gain electrons decreases and so does the reactivity

Reactivity d

ecreases


Displacement reactions

A more reactive halogen will displace a less reactive halide from its compounds in solution.

Chlorine + sodium bromide

Cl2(aq) + 2NaBr(aq)

very pale

green

red colour

sodium chloride + bromine

2

nocolour

NaCl(aq) + Br2(aq)

nocolour


Displacement theory

• The attraction of halogens for an extra electron gets greater going up the group: I <Br<Cl<F.

• If we mix a metal halide with a more reactive halogen, the electron will be transferred from the less to the more reactive halogen.

ClNa+

F-

Cl-Na+

F e-


Reactions with metals

The attraction of halogens for an extra electron means that they readily react with most metals.

Chlorine reacts readily with iron on gentle heating despite iron’s low reactivity.

Chlorine + iron iron (III) chloride

3Cl2(g) + 2Fe(s) FeCl32


Reactions with non-metals

Halogen atoms have 7 electrons in the outer shell.They seek to achieve a full shell (8 electrons).With metals they gain electrons forming ionic compounds.With non-metals they react by sharing electrons and forming covalent compounds.For example, hydrogen and chlorine form hydrogen chloride.

HClClH


Uses of Fluorine

Fluorine, often via hydrogen fluoride, is used to manufacture many other products.

Fluorineand its

compounds

Processing uranium

nuclear fuelFluoridation of

water

Toothpaste,to prevent tooth

decay

fluorine-containing polymers, e.g. Teflon


Uses of Chlorine

pesticides and weed killer

Drinking water treatment

Chlorineand its compounds

HCl

Bleach to kill bacteriaand to make paper

white

antiseptics and disinfectants

Chlorinatedcarbon

compounds, e.g.solvents and

plastics (PVC)


Uses of Bromine and Iodine

Iodine and its compounds

Bromineand its

compounds

medicines

antiseptic

Leaded petrol(being phased out)

agriculture

photography

Animal feed supplements


Uses of Halogens

Link up the halogen with the uses.

BrCl

F I


Across:Across:2 Reactivity does this going

up group 75 Added to animal feeds7 Number of outer shell

electrons in halogens8 Used in the swimming pool9 Used in photography

Down:Down:1 Name for Group 7

Elements3 Most reactive halogen4 Type of compounds formed

with non-metals6 Type of compounds formed

with metals

1

2

3 4

5 6

7

8

9


How many electrons do the halogens have in their outer shell?

A. 1B. 5C. 7D. 8


How many atoms exist in a halogen molecule?

A. 1B. 2C. 5D. 7


What is the order of increasing reactivity of the halogens?

A. F, Cl, I, BrB. F, Cl, Br, I C. I, Cl, Br, FD. I, Br, Cl, F


Which of the pairs of reactants will NOTNOT result in a displacement reaction?

A. Iodine + sodium chlorideB. Fluorine + sodium chlorideC. Chlorine + sodium iodideD. Bromine + sodium iodide


What halogen is used in non-stick cooking pans?

A. FB. ClC. BrD. I


What halogen is used in animal feed?

A. FB. ClC. BrD. I


Astatine comes below iodine in Group 7 What might its melting point be (in oC)?

A. –225 B. +82 C. +150 D. +300

-220

-101

-7

114

-300

-200

-100

0

100

200

300

Period

M.P

t (C

)

F

Cl

Br

I

Documents

© Boardworks Ltd 2003 THE HALOGENS. © Boardworks Ltd 2003 Halogens and the Periodic Table These are the Halogens or Group 7 Elements H Li Na K Rb Cs Fr