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