The Group VIII elements

1. The elements in Group VIII are called the noble gases: helium, neon, argon, krypton, xenon and radon.
2. They sit in the column on the far right of the Periodic Table, at the end of each period.
3. All the noble gases are colourless gases at room temperature and pressure.
4. The noble gases are unreactive, so they have very little tendency to take part in chemical reactions.
5. Helium, neon and argon form no compounds at all under normal conditions.
6. The noble gases are monatomic, so each particle of the gas is a single atom that is not bonded to any other atom.
7. This is why the formula of helium is written as $He$ and the formula of argon as $Ar$, while most other gaseous elements, such as oxygen, $O_2$, and chlorine, ${Cl}_2$, are made of molecules.

Full outer shells

1. Every noble gas atom has a full outer electron shell.
2. Helium has the electronic configuration $2$, and its only shell is full because the first shell holds a maximum of two electrons.
3. Neon has the electronic configuration $2,8$, with eight electrons in its outer shell.
4. Argon has the electronic configuration $2,8,8$, again with eight electrons in its outer shell.
5. Krypton and xenon also have eight electrons in their outer shells.
6. This arrangement is so stable that other atoms gain, lose or share electrons in order to reach the same configuration, which is called a noble gas electronic configuration.

Why the noble gases are unreactive

1. Chemical reactions happen when atoms lose, gain or share electrons to obtain a full outer shell.
2. A noble gas atom already has a full outer shell, so its electronic configuration is already stable.
3. A noble gas atom has no tendency to lose electrons to form a positive ion.
4. A noble gas atom has no tendency to gain electrons, because there is no space for extra electrons in its full outer shell.
5. A noble gas atom has no tendency to share electrons to form a covalent bond.
6. Since the atoms do not need to lose, gain or share electrons, the noble gases are unreactive.

Why the noble gases are monatomic

1. Atoms of other non-metals, such as chlorine, join together by sharing electrons, because sharing completes their outer shells.
2. Noble gas atoms already have full outer shells, so they gain nothing by sharing electrons and do not bond to one another.
3. The atoms therefore stay as separate single atoms, which is what monatomic means.
4. Only very weak forces act between the separate atoms, so the noble gases have very low boiling points and are gases at room temperature.