6.3 Group 0: the noble gases — Edexcel GCSE Chemistry revision notes

6.14, 6.16Group 0

The elements in Group 0 of the periodic table are called the noble gases. They are unreactive and do not easily form molecules because their atoms have stable arrangements of electrons.

The noble gases have eight electrons in their outer shell, except for helium, which has only two electrons.

The boiling points of the noble gases increase with increasing relative atomic mass — that is, going down the group.

Figure: Boiling points down Group 0

Element	Relative atomic mass	Boiling point in degrees C
Helium	4	−269
Neon	20	−246
Argon	40	−186
Krypton	84	−153
Xenon	131	−108

The trend is what matters: as the relative atomic mass rises, so does the boiling point.

Worked example

Radon comes below xenon in Group 0. Predict its boiling point and say whether it is reactive.

Radon has a greater relative atomic mass than xenon, and boiling point increases down the group.
So radon's boiling point must be higher than xenon's −108 degrees C.
A sensible prediction would be somewhere around −60 degrees C — above xenon, but still far below room temperature.
Radon is in Group 0, so its atoms have a stable arrangement of electrons.

Answer: A boiling point above −108 degrees C, and unreactive because it has a stable arrangement of electrons in its outer shell.

You should be able to explain how properties of the elements in Group 0 depend on the outer shell of electrons of the atoms, and predict properties from given trends down the group. When a question hands you a table of data, read the trend off the data you are given rather than reciting a remembered figure — the marks are for using the trend.

Noble gases: the elements in Group 0, which are unreactive and do not easily form molecules because their atoms have stable arrangements of electrons — eight in the outer shell, except helium which has two

6.15–6.16Uses of the noble gases

Every use of a noble gas follows from a property, and the answer has to make that link. Three properties do all the work: they are chemically inert, some of them have a very low density, and none of them is flammable.

Figure: Use and reason

Use	Property it depends on
Argon in filament light bulbs	Inert — it will not react with the hot filament, which would otherwise burn away
Argon shielding an arc weld	Inert — it keeps oxygen away from the hot metal
Helium in balloons and airships	Very low density, and non-flammable, unlike hydrogen
Neon in advertising signs	Inert, and glows brightly when a current passes through it
Helium in deep-sea diving mixtures	Inert — it does not react with the body the way nitrogen does under pressure

The physical properties follow a trend down the group, so they can be predicted the same way the alkali metals' are. Boiling point and density both increase from helium down to xenon, because the atoms get larger and the forces between them get stronger. Given the boiling points of neon and argon, a value for krypton should fall below argon's on the scale — that is, at a higher temperature.

Common mistake

"Because it is a noble gas" is not a reason. Name the property — inert, low density, non-flammable — and then say what that property lets the gas do.

Before you practise

The noble gases have a full outer shell, so they neither gain nor lose electrons and are chemically inert.
Helium has two outer electrons; the rest have eight.
They exist as single atoms, not molecules.
Boiling point and density both increase down the group, because the atoms get larger.
Argon fills light bulbs and shields welds because it is inert; helium fills balloons because it has a very low density and does not burn.
Every 'use' answer needs the property named first, then what it allows.

Now practise it

Reading is the easy half. Answer questions on 6.3 Group 0: the noble gases and find out which parts you actually know.

Written questions Multiple choice