The elements in Group VII are known as halogens. There are 5 kinds of elements in Group VII. There are Fluorine, Chlorine, Bromine, Iodine and Astatine. Most of the time, when we talk about the halogens, we only mean the first four of them: Fluorine, Chlorine, Bromine, and Iodine.
What is halogen?
Why Astatine is not meant when we talk about the halogens?
The Group VII elements are a group of very similar non-metals. The elements are very reactive. Fluorine is the most reactive element in the Periodic Table. The reason for Group VII elements are called the halogens is that they react with most metals to form salt. Halogen is Greek for ‘salt former’.
What is the most reactive element in Periodic Table?
Why the halogen is the very reactive?
Structure of Halogen
The elements consist of small molecules each molecule contains two atoms. The molecules are said to be diatomic. The size of atoms increases, when the proton number increases. Here are the pictures shows the atomic size and ionic size of the four halogens.
How many Chorine ions are there in a Chorine Molecule.
Why the halogens are diatomic.
The melting and boiling points of the elements are low. All the elements boil below 200°C
The boiling points of the elements increase down the group. Fluorine and Chlorine are gases, Bromine is a liquid and Iodine is a solid. The elements also become darker in colour down the group.
Why the melting and boiling points of the elements are low?
Displacement Reactions of the Halogens
The halogens become less reactive down the group. So bromine is less reactive than chlorine, and iodine is less reactive than bromine. A more reactive halogen will displace a less reactive halogen from an aqueous solution of its ions. For example, chlorine displaces iodine from aqueous potassium iodide solution.
The aqueous potassium iodide turns brown due to the iodine produced
This is a redox reaction. The ionic equation is
Electrons are transferred from the iodide ions (I-) to the chlorine molecules (Cl2). So the ions I- are oxidized because they lose electrons and the Cl2 molecules are reduced because they gain electrons. Chlorine behaves as an oxidizing agent in this reaction.
Which is more reactive Chlorine or Fluorine? How do you know?
What is a displacement reaction; please use a formula with A, B, and C to explain?
Compounds of Group VII Elements
The Group Vii elements form compounds with similar formulas. The compounds formed with Group I elements are all ionic. Some examples of Group VII compounds are shown in the table below
One of the most important compounds in sodium chloride, NaCl, often simply called ‘salt’. Sodium Chloride is found in sea water. It can be obtained by evaporating sea water. This method is used in some parts of the world where the climate is hot － the beat from the Sun is used to evaporate the water.
Salt is also found as solid deposits in the ground in some countries. The salt is thus obtained by mining.
Many useful chemicals are made from salt, by passing an electric current through a solution of Sodium Chloride. Two important examples are chlorine and Sodium Hydroxide. This process is called electrolysis.
What is electrolysis?
What are the uses of Sodium Chlorine; please give two examples?
Uses of Group VII Elements and their Compounds
The Group VII elements are important for our health. Small amounts of Fluorine compounds are put into tap water and toothpastes to prevent tooth decay.
Chlorine is put into tap water and swimming pools to destroy harmful microorganisms. We also need chloride ions in our bodies. The salt in our food replaces that lost in sweat and urine.
Very small amounts of iodine are required in our bodies. A deficiency in iodine causes a condition called goiter, which is swelling of the neck. In some countries there is not enough iodine in the food. In those countries iodine is added to the salt used in food to ensure that the people get enough iodine in their bodies.
What element is good for teeth?
How Chlorine destroys harmful microorganisms?
Astatine is an element below iodine in Group VII. The symbol for astatine is At. Use your knowledge of the other elements in Group VII to predict the following properties of astatine.
(a) the physical state and colour under room conditions;
(b) the formula of the compound formed between sodium and astatine;
(c) The number of outer shell electrons in the astatine atoms and the formula of its ion.