Group 0 — The Noble Gases

This lesson covers the Group 0 elements (the noble gases) as required by the Edexcel GCSE Chemistry specification (1CH0), Topic 6: Groups in the Periodic Table. You need to understand why the noble gases are unreactive, know their key physical properties and trends, and recall their uses.

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The Group 0 Elements

Group 0 is found on the far right of the periodic table. These elements are called the noble gases because they are extremely unreactive — they rarely form compounds with other elements.

Element	Symbol	Atomic Number	Electron Configuration	Boiling Point (°C)
Helium	He	2	2	−269
Neon	Ne	10	2, 8	−246
Argon	Ar	18	2, 8, 8	−186
Krypton	Kr	36	2, 8, 18, 8	−153
Xenon	Xe	54	2, 8, 18, 18, 8	−108

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Why Are the Noble Gases Unreactive?

The noble gases have full outer electron shells:

• Helium has 2 electrons in its only shell (which is full with 2).
• Neon has 8 electrons in its outer shell.
• Argon has 8 electrons in its outer shell.
• Krypton and xenon also have 8 electrons in their outer shells.

Because their outer shells are already complete, noble gas atoms have no tendency to:

• Lose electrons (like metals do)
• Gain electrons (like non-metals do)
• Share electrons (like atoms in covalent molecules do)

This means they do not take part in chemical reactions under normal conditions. Their electronic stability is the reason for their inertness.

Exam Tip: The key phrase is "full outer shell of electrons". This is the reason noble gases are unreactive. Do not say "they have 8 outer electrons" for helium — helium has a full outer shell with only 2 electrons.

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Monatomic Gases

Unlike most other gaseous elements, the noble gases exist as single atoms (they are monatomic). They do not form molecules because they have no need to bond with other atoms.

• Other gases like oxygen (O₂), nitrogen (N₂) and chlorine (Cl₂) are diatomic — they exist as molecules of two atoms.
• Noble gases exist as individual atoms: He, Ne, Ar, Kr, Xe.

This is because their full outer shells mean there is no driving force for them to form covalent bonds with each other or with any other element.

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Physical Properties and Trends

The noble gases are all colourless, odourless gases at room temperature.

Trend in Boiling Points

As you go down Group 0, the boiling point increases:

Element	Boiling Point (°C)	Number of Electrons	Relative Atomic Mass
He	−269	2	4
Ne	−246	10	20
Ar	−186	18	40
Kr	−153	36	84
Xe	−108	54	131

Explanation: As you go down the group, the atoms become larger and have more electrons. This means the intermolecular forces (London dispersion forces) between the atoms become stronger. More energy is needed to overcome these forces, so the boiling point increases.

Exam Tip: Even though noble gases are monatomic (single atoms), there are still weak intermolecular forces between the atoms. These are London dispersion forces (also called van der Waals forces). As atoms get bigger with more electrons, these forces get stronger — hence the increase in boiling point.

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Density

The density of noble gases increases down the group because the atoms become heavier (greater atomic mass) while remaining as single atoms.

Element	Approximate Density (g/dm³ at STP)
He	0.16
Ne	0.84
Ar	1.66
Kr	3.48
Xe	5.49

Helium is much less dense than air (approximately 1.2 g/dm³), which is why it is used in balloons and airships.

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Uses of Noble Gases

Because of their unreactivity and other specific properties, noble gases have important practical uses:

Noble Gas	Use	Reason
Helium	Filling balloons and airships	Very low density (lighter than air); unreactive so will not catch fire (unlike hydrogen)
Helium	Deep-sea breathing mixtures (mixed with oxygen)	Does not cause "the bends" like nitrogen; unreactive
Neon	Advertising signs and displays	Glows bright red-orange when electricity passes through it
Argon	Filling incandescent light bulbs	Unreactive — prevents the hot tungsten filament from oxidising and burning out
Argon	Welding (as a shielding gas)	Unreactive — provides an inert atmosphere to prevent the hot metal reacting with oxygen and nitrogen in the air
Krypton	Photographic flash equipment; some laser applications	Produces a bright white light when an electric current passes through it
Xenon	Specialised lamps; some anaesthetic applications	Produces a bright light; low toxicity

Exam Tip: In the exam, when asked why a noble gas is used for a particular purpose, always link your answer back to it being unreactive (full outer shell) and/or another specific physical property (e.g. low density for helium, produces coloured light for neon).

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Discovery of the Noble Gases

The noble gases were not included in early versions of the periodic table because they are so unreactive that they were not discovered until the late 19th century. Argon was discovered in 1894 by Lord Rayleigh and William Ramsay. The other noble gases were discovered shortly afterwards.

When they were discovered, a new group (Group 0) was added to the periodic table. This demonstrated that the periodic table is a working model that can be updated when new evidence is found.

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Comparing Group 0 with Groups 1 and 7

Property	Group 1 (Alkali Metals)	Group 7 (Halogens)	Group 0 (Noble Gases)
Type	Metals	Non-metals	Non-metals
Outer electrons	1	7	Full outer shell (2 or 8)
Bonding tendency	Lose 1 electron → form 1+ ions	Gain 1 electron → form 1− ions	No tendency to bond
Reactivity trend	Increases down group	Decreases down group	Unreactive
Melting/boiling points	Decrease down group	Increase down group	Increase down group
State at room temp	Solids	Gas, liquid, solid	Gases

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Abundance of Noble Gases in the Atmosphere

The noble gases are present in the Earth's atmosphere in small quantities. Argon is by far the most abundant noble gas in the atmosphere.

Noble Gas	Percentage of Atmosphere
Argon	~0.93%
Neon	~0.0018%
Helium	~0.0005%
Krypton	~0.0001%
Xenon	~0.000009%

Noble gases are obtained by the fractional distillation of liquid air. Air is cooled until it liquefies, and the different gases are separated based on their different boiling points.

Exam Tip: If asked how noble gases are obtained, state "fractional distillation of liquid air". This is a common 1-mark question.

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Predicting Properties of Unknown Noble Gases

Using the trends in Group 0, you can predict properties of noble gases you may not have studied:

• Radon (Rn, atomic number 86) is below xenon in the group. You would predict:
  • Higher boiling point than xenon
  • Higher density than xenon
  • Unreactive (full outer shell)
  • Monatomic gas