The halogens презентация

Group 7 – the halogens
The elements in group 7 of the periodic table, on the right, are called the halogens.

Why are they called the ‘halogens’?
Halogens are very reactive non metals.
They are all toxic or harmful because they are so reactive. Before antiseptics, iodine was used to clean wounds as it is harmful to all things, including bacteria.
They are also never found free in nature because of their reactivity – they are found as compounds with metals.
These halogen-metal compounds are salts, which give halogens their name – ‘halo-gen’ means ‘salt-former’.

All halogens have seven electrons in their outer shell.
What is the electron structure of the halogens?
fluorine
2,7
chlorine
2,8,7
bromine
2,8,8,7
They can easily obtain a full outer shell by gaining one electron.
They have similar chemical properties.
They all gain an electron in reactions to form negative ions with a -1 charge.
This means that:

How do halogen molecules exist?
All halogen atoms require one more electron to obtain a full outer shell and become stable.
Each atom can achieve this by sharing one electron with another atom to form a single covalent bond.
This means that all halogens exist as diatomic molecules:
F2, Cl2, Br2 and I2.

poisonous and smelly.
brittle and crumbly when solid
What are the general properties of the halogens?
All the halogens are:
They become darker in colour down the group:
non-metals and so do not conduct electricity

What is the physical state of the halogens?
The melting and boiling points of the halogens increase down the group, as the molecules become bigger.
Halogen
Relative size
Melting point (°C)
Boiling point (°C)
State
-220
-118
-101
-7
114
-34
59
184
gas
gas
liquid
solid
What is the state of each halogen at room temperature?

Halogen vapours
Bromine and iodine are not gaseous, but have low boiling points. This means that they produce vapour at relatively low temperature. They are volatile.
Bromine produces some red-brown vapour, seen here above the liquid bromine in the jar.

How do the halogens react with metals?
The reactivity of halogens means that they readily react with most metals.
Halogens need to gain electrons for a full electron shell and metals need to lose electrons for a full electron shell.
This means that halogens and metals react to form ionic compounds.
nickel (II) chloride
copper (II) chloride
These are metal halides, which are a type of salt.

What are halides?
When halogens react with another substance, they become negative ions, as they are gaining an extra electron.
The name of each of the halogens changes slightly once it has reacted – instead of ending with ‘–ine’, they end with ‘-ide’.
Halogen
Halide
reaction
fluoride (F-)
chloride (Cl-)
bromide (Br-)
iodide (I-)
When this happens, they are called halides.

Equations of halogens and iron
When a halogen reacts with iron it forms an iron halide:
What would the equation be for the reaction that forms iron (III) bromide?
The word and chemical equations for the reaction between chlorine and iron are:

How do the halogens react with non-metals?
Halogens also react with non-metals.
For example, halogens react with hydrogen to create hydrogen halides.
All hydrogen halides are gases. They dissolve easily in water and become strong acids.
Unlike their reactions with metals, halogens share electrons with non-metals, and so react to form covalent compounds.

+

Displacement of halogens
If a halogen is added to a solution of a compound containing a less reactive halogen, it will react with the compound and form a new one.
A more reactive halogen will always displace a less reactive halide from its compounds in solution.
This is called displacement.

Displacement of halogens
Why will a halogen always displace a less reactive halogen?

Displacement theory
If a metal halide is mixed with a more reactive halogen,
the extra electron will be transferred from the less reactive to the more reactive halogen.
sodium
chloride
fluorine
fluoride
chlorine

Displacement reactions: summary
The reactions between solutions of halogens and metal halides (salts) can be summarised in a table:
2KCl + I2
2KBr + I2
2KCl + Br2
no reaction
no reaction
no reaction

What are the uses of halogens?