Group 7 Elements The Halogens

Group 7 – the halogens The elements in group 7 of the periodic table, on the right, are called the halogens. fluorine chlorine bromine iodine astatine I Br Cl F At

What are the halogens?

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: F 2, Cl 2, Br 2 and I 2. +  F F F F

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 is pale yellow is green-yellow is blue-black. is red-brown

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 gas liquid solid What is the state of each halogen at room temperature?

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’. HalogenHalidereaction fluoride (F - ) chloride (Cl - ) bromide (Br - ) iodide (I - ) (F) (Cl) (Br) (I) When this happens, they are called halides.

Halogens reacting with iron wool

What is the order of reactivity ?

How does electron structure affect reactivity? The reactivity of alkali metals decreases going down the group. What is the reason for this? The atoms of each element get larger going down the group. This means that the outer shell gets further away from the nucleus and is shielded by more electron shells. The further the outer shell is from the positive attraction of the nucleus, the harder it is to attract another electron to complete the outer shell. This is why the reactivity of the halogens decreases going down group 7. decrease in reactivity F Cl Br

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. sodium chloride sodium fluoride chlorinefluorine ++  F 2 (aq)2NaCl (aq)2NaF (aq)Cl 2 (aq) ++  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 reactions of halogens

Displacement reactions: Summary The reactions between solutions of halogens and metal halides (salts) can be summarised in a table: 2KCl + I 2 2KBr + I 2 halogen chlorine bromine iodine salt (aq) potassium chloride potassium iodide potassium bromide 2KCl + Br 2 no reaction

Is there a displacement reaction?

Halogen Displacement Chlorine water Bromine water Iodine waterKBr added KI added KCl added KI added KCl added KBr added Colour change Yes Yes No Yes No No Write an equation to show the reactions which are taking place in tubes 1,2 and 4

Reactions of halogens: Summary

What are the uses of halogens?

How many everyday uses of halogens can you see below? What are the uses of halogens?