Physical properties of the halogens
The vertical column of non-metal elements next to group 0 in the periodic table, also called the halogens. contains Element that is a poor conductor of electricity and heat, and which forms acidic oxides. A substance made of one type of atom only. placed in 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 elements in group 7 are 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 A description of the appearance of a substance or how it acts without involving chemical reactions. For example, state, melting point, conductivity, etc. and A description of how a substance reacts with other substances. For example, flammability, pH, reaction with acid, etc..
Learn more on groups in the periodic table in this podcast.
Listen to the full series on 大象传媒 Sounds.
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.
| Element | Colour | State |
| Chlorine, Cl2 | Pale green | Gas |
| Bromine, Br2 | Brown | Liquid |
| Iodine, I2 | Purple-black | Solid |
| Element | Chlorine, Cl2 |
|---|---|
| Colour | Pale green |
| State | Gas |
| Element | Bromine, Br2 |
|---|---|
| Colour | Brown |
| State | Liquid |
| Element | Iodine, I2 |
|---|---|
| Colour | Purple-black |
| State | Solid |
The The temperature at which a solid changes into a liquid as it is heated. 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掳C and a boiling point of about 340掳C. This means that it will be solid at room temperature.