Physical properties of the halogens
The vertical column of non-metal elements next to group 0 in the periodic table, also called the halogens. (IUPAC group 17) is a vertical column on the right of the A tabular representation of all known elements in order based on atomic number, eg all the noble gases are found on the right of the periodic table.. The A substance made of one type of atom only. in group 7 are Element that is a poor conductor of electricity and heat, and which forms acidic oxides. called the An element placed in group 7 of the periodic table, which starts with fluorine and ends with astatine. The name 'halogen' means 'salt-producing' because halogens produce a range of salts when they react with metals..
The halogens show trends in their physical and chemical The characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point..
Physical properties
The halogens exist as simple A collection of two or more atoms held together by chemical bonds.. Each molecule contains two halogen The smallest part of an element that can exist. joined by a single A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.. The table shows the colour and physical Solid, liquid or gas. Evaporation is a change of state from liquid to gas. of chlorine, bromine and iodine at room temperature.
| Group 7 element | Colour | State |
| Chlorine, Cl2 | Pale green | Gas |
| Bromine, Br2 | Brown | Liquid |
| Iodine, I2 | Purple-black | Solid |
| Group 7 element | Chlorine, Cl2 |
|---|---|
| Colour | Pale green |
| State | Gas |
| Group 7 element | Bromine, Br2 |
|---|---|
| Colour | Brown |
| State | Liquid |
| Group 7 element | Iodine, I2 |
|---|---|
| Colour | Purple-black |
| State | Solid |
The melting points and The temperature at which a substance rapidly changes from a liquid to a gas. of the halogens increase going down group 7. This is because, going down group 7:
- the molecules become larger
- the Weak attractive forces between molecules. When a simple molecular substance melts or boils, it is the intermolecular forces that are broken (not the covalent bonds in each molecule). become stronger
- more The capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow. is needed to overcome these forces
Example
The graph shows the melting and boiling points of the first four group 7 elements. Astatine is placed below iodine in group 7. Predict the melting and boiling points of astatine and its state at room temperature.
Astatine should have a melting point of about 300°C and a boiling point of about 340°C. This means that it will be solid at room temperature.
