What are Noble Gases?

Introduction

The noble gases, also known as the inert gases and aerogens, are the elements that belong to group 18 of the modern periodic table. The elements that belong to this group are:

• Helium (He)
• Neon (Ne)
• Argon (Ar)
• Krypton (Kr)
• Xenon (Xe)
• Radon (Rn)

Under standard conditions for temperature and pressure, all the noble gases exist in the gaseous phase. They are known to possess extremely low chemical reactivity (hence the name inert gas). This is because all the noble gases have stable electronic configurations. This is the reason why noble gases do not form molecules easily and are mostly found as mono-atomic gases.

The general electronic configuration of the noble gases can be written as ‘ns²np⁶’. Therefore, the outermost valence shells of the noble gases can be considered as ‘full’. This is the reason behind the chemically inert nature of the group 18 elements.

Table of Contents

• Properties of Helium (He)
• Properties of Neon (Ne)
• Properties of Argon (Ar)
• Properties of Krypton (Kr)
• Properties of Xenon (Xe)
• Properties of Radon (Rn)

Properties of Helium (He)

Helium is a chemical element which is denoted by the symbol He. The atomic number of helium is 2. Under standard conditions for temperature and pressure (STP), helium exists as a colourless monoatomic gas that does not have any distinct odour or taste. It can be noted that helium is non-toxic in small concentrations. It is the first and the lightest noble gas. Among all elements, helium is known to possess the lowest boiling point.

Helium is an s-block element which corresponds to period 1 and group 18 of the modern periodic table. The electron configuration of helium is 1s². Therefore, this element has a total of 2 electrons in its valence shell. The melting point of helium is approximately equal to 0.95 Kelvin (or -272.20 degrees Celsius) when it is placed under a pressure of 2.5 MPa. Under standard conditions for temperature and pressure, the density of this element corresponds to 1.7186 grams per litre. However, in its liquid state, the density of this element is approximately equal to 0.145 grams per cubic centimetre.

Properties of Neon (Ne)

Neon is a chemical element which is denoted by the symbol Ne. the atomic number of neon is 10. Under standard conditions for temperature and pressure (STP), neon exists as a colourless mono atomic gas (similar to helium). This gas does not possess any characteristic odour. Neon is the second-lightest noble gas, the lightest being helium.

Neon belongs to group 18 and period 2 of the modern periodic table. The electron configuration of this element is [He] 2s²2p⁶. It holds a total of 8 electrons in its valence shell. The melting point of neon is approximately equal to 24.56 Kelvin (or -248.59 degrees Celsius). On the other hand, the boiling point of neon is equal to 27.104 Kelvin (or -246.046 degrees Celsius). At STP, the density of this gas corresponds to 0.9 grams per litre (approximately). However, in its liquid state (at a temperature equal to its boiling point), the density of neon is equal to 1.207 grams per cubic centimetre.

The triple point of neon occurs at a temperature of 24.556 Kelvin and under a pressure of 43.37 kilopascals. The enthalpy of fusion of this element is equal to 0.335 kilojoules per mole. It can be noted that the latent heat of vaporisation of neon is equal to 1.71 kilojoules per mole.

Properties of Argon (Ar)

Argon is the 3rd noble gas whose atomic number is equal to 18. This element is denoted by the symbol Ar. In the Earth’s atmosphere, argon is known to be the third-most abundant gas. Under standard conditions for temperature and pressure, argon is known to exist as a colourless gas that exhibits a violet or lilac-coloured glow when it is placed in an electric field.

Argon is a p-block element that corresponds to group 18 and period 3 of the modern periodic table. The electronic configuration of argon is [Ne]3s²3p⁶. This element has a total of 8 electrons in its valence shell. The melting point of argon corresponds to 83.81 Kelvin whereas its boiling point corresponds to 87.302 Kelvin. Under standard conditions for temperature and pressure, the density of argon is roughly equal to 1.784 grams per litre.

Properties of Krypton (Kr)

Krypton is the 4th noble gas. The atomic number of krypton is 36. This element is often denoted by the symbol Kr. Under standard conditions for temperature and pressure, krypton exists as a colourless monoatomic gas that does not have any characteristic odour. This gas is also known to be tasteless.

Krypton, like argon, is a p-block element. It corresponds to group 18 and period 4 of the modern periodic table. The electron configuration of krypton can be written as [Ar]3d¹⁰4s²4p⁶. The melting point of this element is approximately equal to 115.78 Kelvin whereas the boiling point of this element is equal to 119.3 Kelvin. At STP, the density of this element is roughly equal to 3.75 grams per litre.

Properties of Xenon (Xe)

Xenon, the 5th noble gas, has an atomic number of 54. The symbol ‘Xe’ is often employed to denote xenon. Under standard conditions, this element is known to exist as a mono atomic gas that is colourless and odourless. This p-block element corresponds to period 5 and group 18 of the modern periodic table.

The electronic configuration of xenon is [Kr]4d¹⁰5s²5p⁶. The melting point of xenon is equal to 161.4 Kelvin whereas the boiling point of this element is equal to 165.05 Kelvin. At STP, the density of xenon is roughly equal to 5.89 grams per litre.

Properties of Radon (Rn)

Radon is a noble gas whose atomic number is 86. The symbol of this element is Rn. Under standard conditions, radon (like most other noble gases) is a colourless and odourless gas that does not have any characteristic taste. It is important to note that radon is radioactive. In fact, the most stable isotope of radon, which is ²²²Rn, is known to have a half-life of 3.8 days.

Radon is a p-block element that corresponds to group 18 and period 6 of the modern periodic table. The electronic configuration of this element is [Xe]4f¹⁴5d¹⁰6s²6p⁶. The melting and boiling points of radon are 202 Kelvin and 211.5 Kelvin respectively.

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