Download Chlorine - WordPress.com

THE HALOGENS
© Boardworks Ltd 2003
Halogens and the Periodic Table
These are the Halogens or Group 7 Elements
H
He
Li Be
B C N O F Ne
Na Mg
Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac Rf Db Sg Bh Hs Mt ? ? ?
© Boardworks Ltd 2003
Electronic Structure
All the Group 7 elements have 7 electrons in the
outermost shell.
F
Fluorine
Cl
Chlorine
2,7
2,8,7
Br
Bromine
I
Iodine
At
Astatine
And so on
© Boardworks Ltd 2003
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
F
F
F
© Boardworks Ltd 2003
Patterns: colour
The group 7 elements get darker as you go down
the group.
F
Darker
Cl
Br
I
Bromine
solution.
Note the
bromine
vapour
above the
liquid
What colour would you expect astatine to be?
© Boardworks Ltd 2003
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
Boiling Physical
Point (oC) Point (oC)
State
Fluorine
-220
-188
gas
Chlorine
-101
-35
gas
Bromine
-7
59
liquid
+114
184
solid
Iodine
© Boardworks Ltd 2003
Patterns: reactivity
Reactivity increases up the group.
Cl
Br
I
At
Increasing Reactivity
F
For example, their reaction with
hydrogen
F2
Cl2
Br2
I2
Reacts instantly even at 200 C
Reacts slowly in
dark.Explodes in light
Needs heating to +200 C in
order to react
Does not react completely
even at 500 C
How will Astatine react?
© Boardworks Ltd 2003
Reactivity and electron structures
Most halogen reactions involve gaining an electron.
Reactivity decreases
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
© Boardworks Ltd 2003
Displacement reactions
A more reactive halogen will displace a less reactive halide
from its compounds in solution.
Chlorine + sodium bromide  sodium chloride + bromine
Cl2(aq) + 2NaBr(aq)  2 NaCl(aq) + Br2(aq)
very
pale
green
no
colour
no
colour
red
colour
© Boardworks Ltd 2003
Displacement theory
• The attraction of halogens for
an extra electron gets
greater going up the group:
I <Br<Cl<F.
Na+
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.
Na+
e-
Cl
F-
© Boardworks Ltd 2003
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)  2 FeCl3
© Boardworks Ltd 2003
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.
H
Cl
Cl
H
© Boardworks Ltd 2003
Uses of Fluorine
Fluorine, often via hydrogen fluoride, is used to
manufacture many other products.
Fluorine
and its
compounds
Processing
uranium
nuclear fuel
Toothpaste,
to prevent tooth
decay
Fluoridation of
water
fluorine-containing
polymers, e.g. Teflon
© Boardworks Ltd 2003
Uses of Chlorine
antiseptics and
disinfectants
pesticides
and weed killer
Chlorine
and its compounds
Bleach to kill bacteria
and to make paper
white
Drinking water treatment
HCl
Chlorinated
carbon
compounds, e.g.
solvents and
plastics (PVC)
© Boardworks Ltd 2003
Uses of Bromine and Iodine
Leaded petrol
(being phased out)
Bromine
and its
compounds
medicines
photography
agriculture
Iodine and its
compounds
antiseptic
Animal feed
supplements
© Boardworks Ltd 2003
Uses of Halogens
Link up the halogen with the uses.
F
I
Cl
Br
© Boardworks Ltd 2003
Across:
2 Reactivity does this going
up group 7
5 Added to animal feeds
7 Number of outer shell
electrons in halogens
8 Used in the swimming pool
9 Used in photography
Down:
1 Name for Group 7
Elements
3 Most reactive halogen
4 Type of compounds formed
with non-metals
6 Type of compounds formed
with metals
1
2
3
5
4
6
7
8
9
© Boardworks Ltd 2003
How many electrons do the halogens have in
their outer shell?
A.
B.
C.
D.
1
5
7
8
© Boardworks Ltd 2003
How many atoms exist in a halogen molecule?
A.
B.
C.
D.
1
2
5
7
© Boardworks Ltd 2003
What is the order of increasing reactivity of the
halogens?
A.
B.
C.
D.
F, Cl, I, Br
F, Cl, Br, I
I, Cl, Br, F
I, Br, Cl, F
© Boardworks Ltd 2003
Which of the pairs of reactants will NOT result
in a displacement reaction?
A.
B.
C.
D.
Iodine + sodium chloride
Fluorine + sodium chloride
Chlorine + sodium iodide
Bromine + sodium iodide
© Boardworks Ltd 2003
What halogen is used in non-stick cooking
pans?
A.
B.
C.
D.
F
Cl
Br
I
© Boardworks Ltd 2003
What halogen is used in animal feed?
A.
B.
C.
D.
F
Cl
Br
I
© Boardworks Ltd 2003
Astatine comes below iodine in Group 7
What might its melting point be (in oC)?
A. –225
B. +82
C. +150
D. +300
300
M.Pt (C)
200
114
I
100
0
-100
-200
-300
-101
Cl
-7
Br
-220
F
Period
© Boardworks Ltd 2003