Section 1 of 7Meet the noble gases
Members
- Members Helium, neon, argon, krypton, xenon and radon make up Group 0 on the far right of the periodic table.
- Radon is radioactive and is rarely handled in school.
Physical properties
- Physical properties All are colourless gases at room temperature.
- They are monatomic, existing as single atoms rather than molecules.
Low boiling points
- Low boiling points Very weak forces between atoms mean very little energy is needed to separate them.
- Helium has the lowest boiling point of any element, about -269 °C.
Section 2 of 7Why they are unreactive
1Full outer shell
- Full outer shell Helium has two electrons; the others have eight outer electrons.
2Stable arrangement
- Stable arrangement Atoms have no need to gain, lose or share electrons, because their electron arrangement is already stable.
3Do not form compounds
- Do not form compounds They exist as separate atoms and are inert in most conditions.
Section 3 of 7Trend down the group
| Property | Going down Group 0 | Reason |
|---|---|---|
| Atomic size | Increases | More electron shells |
| Boiling point | Increases | Larger atoms have stronger forces between them, needing more energy to separate |
| Density | Increases | Each atom has a greater mass |
| Reactivity | Remains negligible | Outer shell stays full |
Section 4 of 7Uses linked to properties
Noble gas uses
Helium
- Helium Less dense than air and non-flammable, so used in airships and balloons.
Argon
- Argon Inert, so it fills filament lamps and protects metal during welding.
Neon
- Neon Glows when electricity passes through it, so used in bright signs.
Section 5 of 7Worked example: predicting a missing value
1
Suppose the boiling points of neon and krypton are about -246 °C and -153 °C.
2
Argon lies between them in the group, so its boiling point must lie between these values.
3
The real value is about -186 °C, which fits the trend of boiling points rising down the group.
4
Explain it by saying the larger atoms have stronger attractions between them, so more energy is needed to separate them.
5
State that the boiling point is a physical change, so no covalent bonds are broken.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Noble gas | An element in Group 0, with a full outer shell and very low reactivity. |
| Monatomic | Existing as single, unbonded atoms. |
| Inert | Not reacting under normal conditions. |
| Boiling point | The temperature at which a liquid changes to a gas. |
| Outer shell | The highest-energy occupied electron shell of an atom. |
| Group | A vertical column of the periodic table containing elements with similar properties. |
Section 7 of 7Exam technique
1
Saying noble gases are unreactive because they are gases; the cause is their full outer shell.
2
Writing that they are diatomic molecules like oxygen; they are single atoms.
3
Reversing the trend, since boiling points rise, not fall, as you go down the group.
4
Explaining boiling-point change by breaking covalent bonds; only weak forces between atoms are overcome.
5
Stating that all noble gases have eight outer electrons. Helium has two.