Group 0: the noble gases

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Chemistry · Electron shells

Switch atom ↑, then tap a shell

Helium: two electrons in the first shell, which is its outer shell. Full.

Switch between helium and neon, then tap each shell to see why it counts as full.

Predict, then check

Noble gases are single atoms with weak forces of attraction between them. To boil, those forces have to be overcome.

Helium is at the top of Group 0. Xenon is near the bottom. Which one boils at the higher temperature, and why?

Chemistry · Density

Float or sink? The noble gas balloon test

Fill a balloon with each noble gas and let it go. Where does each one belong?

5 of 5 still to sort.

Density is how much mass is packed into each unit of volume. As gases, the noble gases have their particles spaced quite far apart, so they all have low densities. The question is how each one compares with the air around it, because a substance with a lower density is pushed upwards by one with a higher density.

What you need to know

• Group 0 is the column on the far right of the periodic table. From the top: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn) and, more recently, oganesson. The atomic number increases going down.
• Every noble gas atom has a full outer shell of electrons. Helium has two electrons in its first shell; neon has eight in its second shell.
• A full outer shell makes the atom stable. It doesn't need to gain or lose electrons or bond with other atoms, so noble gases exist as single atoms (monoatomic) and are unreactive (inert) and non-flammable.
• They are colourless gases at room temperature; argon, for example, is present in small amounts in the air we breathe. Oganesson is the exception: only a few atoms have been made, it is very highly radioactive, and it is predicted to be a solid.
• When electricity passes through them they glow different colours: neon a reddish orange, argon violet.
• Going down the group, atomic mass, density and boiling point all increase.
• Uses: argon shields hot metal in welding, and argon or xenon filled old filament light bulbs. Helium is used in balloons, breathing mixtures and cooling devices; neon in neon signs and high-voltage indicators; krypton in lighting and photographic flashes; xenon in flash lamps and ion propulsion systems.

The big picture

The noble gases are Group 0, the far-right column of the periodic table. Every atom has a full outer shell of electrons, so it is stable: it doesn't need to bond, exists as single atoms, and is unreactive and non-flammable. Going down the group the atoms get heavier, so mass and density increase; they also get bigger and attract each other more strongly, so boiling point increases. These properties explain their uses, from welding and old light bulbs to balloons and glowing signs.

⚠ Watch out

Calling noble gases 'molecules' and thinking that boiling one means breaking bonds. Noble gases are single atoms with no bonds between them, only weak forces of attraction. Boiling overcomes those weak forces, and 'no bonds' does not mean 'no forces'.

Memory hook

Full shell, no deal: a noble gas atom already has a full outer shell, so it doesn't need to gain or lose electrons, or bond with anything. Then, going down: heavier, denser, harder to boil. He floats, Xe sinks.

Check yourself

Without looking back: list the Group 0 elements from the top, explain in three linked steps why they're unreactive, and say how density and boiling point change down the group.