L.O: To be able to explain the properties and patterns of reactivity of the halogens Starter: Choose...
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Transcript of L.O: To be able to explain the properties and patterns of reactivity of the halogens Starter: Choose...
L.O: To be able to explain the properties and patterns of reactivity of the halogens
Starter:
Choose a halogen and draw the electronic structure of it.
What do the halogens do when they react?
Challenge: can you write a half equation to show this?
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
Aluminium and chlorinehttp://www.youtube.com/watch?v=aK85PZX2xNE
Aluminium and bromine http://www.youtube.com/watch?v=zZAiY
c3WVXM
Can you hypothesis why there are these differences
These symbols are used in some equations:
(aq) aqueous solution(l) Liquid(s) Solid(g) Gas
e.g. 2K(s) + 2H2O (l) → 2KOH(aq) + H2(g)
practical
Reactivity increases up the group.
F
Cl
Br
I
At Incr
easi
ng R
eact
ivit
y
For example, their reaction with hydrogen
F2Reacts instantly even at
-200ºC
Cl2 Reacts slowly in dark.Explodes in light
Br2Needs heating to +200ºC in order to react
I2Does not react completely even at 500ºC
How will Astatine react?
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
Reactiv
ity d
ecre
ases
The group 7 elements get darker as you go down the group.
F
Cl
Br
I
Dark
er
Bromine solution.
Note the bromine vapour above the liquid
What colour would you expect astatine to be?
What patterns does this data show?
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
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
As you go DOWN the group
Halogens get Less REACTIVE as you go DOWN the group (larger atoms gain electrons less easily)
The shells provide SHEILDING from the positive pull of the nucleus so it becomes HARDER to pull in an electron
The HIGHER the MELTING / BOILING point
The Halogens
F
AtI
BrCl
Have Coloured Vapours (getting darker down the group)
A more reactive halogen can DISPLACE a less reactive halogen
from an aqueous solution
Form -1 ions by GAINING one electron
Form covalent bonds with each other to form DIATOMIC Molecules
Halogens get _______ REACTIVE as you go DOWN the group.
The shells provide __________from the positive pull of the nucleus so it becomes HARDER to pull in an electron
A more reactive halogen can ________ a less reactive halogen from an aqueous solution
The coloured vapours get getting ________ down the group
The Halogens - Summary F
AtI
BrCl
Link up the halogen with the uses.
BrCl
F I