What are the characteristic properties of Group VII halogens?

Group VII halogens are non-metals, highly reactive, have seven electrons in their outer shell, and form salts when combined with metals.

Group VII elements, also known as halogens, are located on the far right of the periodic table. They are non-metals, which means they are poor conductors of heat and electricity, are not malleable or ductile, and have low melting and boiling points compared to metals. They exist in all three states of matter at room temperature: Fluorine and Chlorine are gases, Bromine is a liquid, and Iodine and Astatine are solids.

Halogens are highly reactive due to having seven electrons in their outer shell. They need only one more electron to achieve a stable electron configuration, which makes them very eager to react with other elements. This high reactivity decreases as you move down the group, with Fluorine being the most reactive and Astatine the least.

When halogens react with metals, they form salts. For example, when Sodium (a metal) reacts with Chlorine (a halogen), it forms Sodium Chloride, which is common table salt. This is because halogens gain an electron from the metal during the reaction, resulting in the formation of a negative ion. The metal, on the other hand, loses an electron and forms a positive ion. These opposite charges attract each other, forming an ionic bond and resulting in a salt.

Halogens also have distinctive colours and smells. Fluorine is a pale yellow gas, Chlorine is a green gas, Bromine is a red-brown liquid, and Iodine is a grey solid or purple vapour. They all have strong, unpleasant smells, which can be toxic or even lethal in high concentrations. Therefore, it's important to handle these elements with care in the lab.