View
243
Download
6
Category
Preview:
Citation preview
© 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
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
© Boardworks Ltd 2003
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
© 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 FF F
© Boardworks Ltd 2003
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?
© 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 Point (oC)
Boiling Point (oC)
Physical State
Fluorine -220 -188
Chlorine -101 -35
Bromine -7 59
Iodine +114 184
gas
gas
liquid
solid
© Boardworks Ltd 2003
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?
© Boardworks Ltd 2003
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
© Boardworks Ltd 2003
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
© Boardworks Ltd 2003
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-
© 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) FeCl32
© 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.
HClClH
© Boardworks Ltd 2003
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
© Boardworks Ltd 2003
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)
© Boardworks Ltd 2003
Uses of Bromine and Iodine
Iodine and its compounds
Bromineand its
compounds
medicines
antiseptic
Leaded petrol(being phased out)
agriculture
photography
Animal feed supplements
© Boardworks Ltd 2003
Uses of Halogens
Link up the halogen with the uses.
BrCl
F I
© Boardworks Ltd 2003
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
© Boardworks Ltd 2003
How many electrons do the halogens have in their outer shell?
A. 1B. 5C. 7D. 8
© Boardworks Ltd 2003
How many atoms exist in a halogen molecule?
A. 1B. 2C. 5D. 7
© Boardworks Ltd 2003
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
© Boardworks Ltd 2003
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
© Boardworks Ltd 2003
What halogen is used in non-stick cooking pans?
A. FB. ClC. BrD. I
© Boardworks Ltd 2003
What halogen is used in animal feed?
A. FB. ClC. BrD. 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
-220
-101
-7
114
-300
-200
-100
0
100
200
300
Period
M.P
t (C
)
F
Cl
Br
I
Recommended