Section 2 a) Key Words

Acid: A substance with a low pH (less than 7). The lower the pH, the more acidic (due to more H+ ions). Can neutralise bases and form salts.

Alkali metals: Metals in group 1 of the periodic table; they have 1 valence electron. They are highly reactive and form very strongly basic hydroxides.

Base: A substance with a high pH (more than 7). The higher the pH, the more basic (due to more OH- ions). Also known as alkalies, they can neutralise acids and form salts.

Diatomic molecules: Molecules that are comprised of two atoms.

Group: The columns of the periodic table. Elements of the same group have the same number of valence electrons.

Halogens: Elements in the 7th group of the periodic table. They have seven valence electrons, and are all non-metals, whose hydroxides are strongly acidic.

Inert: A substance that does not react. Noble gases are unreactive, therefore they are inert.

Metal: Elements that conduct electricity and heat, and whose hydroxides are basic. They bond together in a giant metallic crystal, with a sea of free electrons.

Noble gas: An element in the last group of the periodic table, group 0 or group 8. It is inert, and has a full outer shell of electrons

Non-metal: Elements that generally do not conduct electricity (carbon is an exception). Form covalent bonds involving a shared pair of electrons, and their hydroxides are acidic.

Period: The rows of the periodic table. Indicates how many shells of electrons there are.

Periodic table: A table of organisation for the chemical elements, developed by Mendeleev  (though not quite as we know it today, and there are many other versions)

Valence electrons: Outer-shell electrons