Chemical families: alkali metals, halogens and noble gases

0:00There are over a hundred elements. Which ones behave alike?

0:05Here are the first four rows of the periodic table. Each row is a period, and each column is a group.

0:13Elements in a group tend to react in similar ways, so a group is called a chemical family.

0:19Apart from hydrogen, group 1 holds the alkali metals, such as lithium, sodium and potassium.

0:27They are soft metals that react strongly with water.

0:31Down the group the reaction gets stronger: lithium fizzes, sodium fizzes faster, and potassium catches fire.

0:40Group 2 holds the alkaline earth metals. They are reactive too, but less than group 1.

0:47Group 17 holds the halogens, very reactive non-metals such as fluorine, chlorine and bromine.

0:55Halogens react with metals to make salts: sodium and chlorine make sodium chloride, table salt.

1:03Group 18 holds the noble gases. Their outer shell of electrons is full, so they barely react.

1:11Why? Atoms react using their outer electrons, the ones in the outermost shell, like this one in lithium.

1:19Alkali metals have one outer electron, alkaline earth metals two, halogens seven, and noble gases a full shell: eight, or two for helium.

1:31But elements in the same row do not behave alike. In period 3, sodium is a reactive metal, chlorine a reactive non-metal, and argon barely reacts.

1:42So chemical families run down the columns: same group, similar reactions.