Edexcel GCSE Chemistry (1CH0) — Groups in the Periodic Table
Have you ever wondered why a helium balloon floats away if you let it go, or why the glowing metal inside a traditional light bulb does not instantly catch fire? The answer lies in the unique properties of Group 0 elements, also known as the noble gases. These gases are entirely inert, meaning they are chemically unreactive.
Their unreactive nature comes directly from their atomic structure. Every noble gas possesses a full outer shell of electrons (helium has 2 electrons in its only shell, while the others have 8). Because their valence shells are completely full, they have no tendency to lose, gain, or share electrons to achieve chemical stability.
Consequently, noble gases do not form compounds or diatomic molecules like oxygen gas (). Instead, they are monatomic, meaning they exist as single, unattached atoms moving freely on their own.
While all noble gases share chemical similarities—they are unreactive, colourless, and non-flammable (unable to catch fire)—their physical traits change as you move down the group. The of the atoms steadily increases from helium down to radon.
As the atoms get larger and heavier, the density (the mass per unit volume) of the gas increases. Helium is significantly less dense than air, which gives it buoyancy. In contrast, argon, krypton, and xenon are considerably denser than air.
The boiling points also increase as you move down the group. This happens because larger atoms have stronger intermolecular forces between them, which require more thermal energy to overcome.
Examiners expect you to clearly link a specific physical or chemical property of a noble gas directly to its everyday application.
Explain why argon is used to fill traditional filament light bulbs instead of leaving them filled with air. (3 marks)
Step 1: Identify the chemical property of the gas inside the bulb.
Step 2: Identify the danger of using standard air.
Step 3: Link the property to the prevention of a negative outcome.
Students often state that all noble gases have '8 electrons in their outer shell'. Remember that helium is the exception—it has a full outer shell with only 2 electrons.
When explaining why helium is used in balloons, avoid simply saying 'it is light'. To secure the mark, you must use the correct scientific terminology: 'it is less dense than air'.
In 3-mark or 4-mark 'Explain' questions about argon in light bulbs or welding, you must explicitly state that using air would expose the metal to oxygen, causing oxidation. Mentioning the negative consequence of oxygen is usually worth a specific mark.
Inert
Chemically unreactive; a substance that does not readily undergo chemical reactions, typically because it already possesses a stable electronic structure.
Full outer shell
A valence shell that contains the maximum possible number of electrons (2 for the first shell, 8 for subsequent shells), providing maximum atomic stability.
Monatomic
A gas consisting of single, uncombined atoms rather than molecules.
Non-flammable
A substance that does not catch fire or burn when exposed to a flame.
Relative atomic mass (Aᵣ)
The average mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12.
Density
The mass per unit volume of a substance, which determines whether a gas will float or sink in air.
Shielding gas
An inert gas (often argon) used in welding to protect the weld pool from reactive atmospheric gases like oxygen and nitrogen.
Oxidation
A chemical reaction where a substance combines with oxygen, such as a hot metal filament burning out in air.
Put your knowledge into practice — try past paper questions for Chemistry
Inert
Chemically unreactive; a substance that does not readily undergo chemical reactions, typically because it already possesses a stable electronic structure.
Full outer shell
A valence shell that contains the maximum possible number of electrons (2 for the first shell, 8 for subsequent shells), providing maximum atomic stability.
Monatomic
A gas consisting of single, uncombined atoms rather than molecules.
Non-flammable
A substance that does not catch fire or burn when exposed to a flame.
Relative atomic mass (Aᵣ)
The average mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12.
Density
The mass per unit volume of a substance, which determines whether a gas will float or sink in air.
Shielding gas
An inert gas (often argon) used in welding to protect the weld pool from reactive atmospheric gases like oxygen and nitrogen.
Oxidation
A chemical reaction where a substance combines with oxygen, such as a hot metal filament burning out in air.
