No Slide TitleThese 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
Br
Ca
Kr
Y
Zr
Nb
Mo
Tc
Ru
Pd
Ag
Cd
In
Sn
Sb
Sr
Te
Rh
Ba
Hf
Ta
W
Re
Os
Ir
Au
Hg
Tl
Pb
Bi
Po
La
At
Pt
Ra
Rf
Db
Sg
Bh
Hs
Mt
Electronic Structure
All the Group 7 elements have 7 electrons in the outermost shell.
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
F
F
F
Patterns: colour
The group 7 elements get darker as you go down the group.
What colour would you expect astatine to be?
F
Cl
Br
I
Darker
a
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Patterns: physical state
Melting Points and boiling points increase as the molecules get bigger.
What is the physical state: solid, liquid or gas?
gas
gas
liquid
solid
Element
Size
How will Astatine react?
F2
Cl2
Br2
I2
F
Cl
Br
I
At
Most halogen reactions involve gaining an electron.
The atoms get bigger as you go down the group. This reduces the attraction of the (+) nucleus for an additional (-) electron.
‘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 decreases
Displacement reactions
A more reactive halogen will displace a less reactive halide from its compounds in solution.
Chlorine + sodium bromide
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.
Na+
Na+
F
Cl
F-
Cl-
e-
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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.
3Cl2(g) + 2Fe(s)
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Reactions with non-metals
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.
Cl
H
Cl
H
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Uses of Fluorine
Fluorine, often via hydrogen fluoride, is used to manufacture many other products.
Fluorine
Iodine and its compounds
Br
Cl
F
I
5 Added to animal feeds
7 Number of outer shell electrons in halogens
8 Used in the swimming pool
9 Used in photography
3 Most reactive halogen
1
2
3
4
5
6
7
8
9
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How many electrons do the halogens have in their outer shell?
1
5
7
8
1
2
5
7
What is the order of increasing reactivity of the halogens?
F, Cl, I, Br
F, Cl, Br, I
I, Cl, Br, F
I, Br, Cl, F
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Which of the pairs of reactants will NOT result in a displacement reaction?
Iodine + sodium chloride
Fluorine + sodium chloride
Chlorine + sodium iodide
Bromine + sodium iodide
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F
Cl
Br
I
F
Cl
Br
I
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Astatine comes below iodine in Group 7 What might its melting point be (in oC)?
A. –225 B. +82 C. +150 D. +300
Chart1
Fluorine
Chlorine
Bromine
Iodine
Astatine
F
Cl
Br
I