What is Noble Gases?
Do you know it's helium gas that is filled in the balloons we used to play with? Helium is a noble gas but its properties are quite different from the properties of other noble gases. Group 18 elements consist of the noble gases which were not known at the time of Mendeleev and so were not added to the Mendeleev's periodic table but later after the discovery of helium and argon in the periodic table Ramsay in 1896 suggested a new group for such noble gases.
The new group formed was known as the zero group having 6 electrons in it. These elements came to be known as noble gases, inert gases, the zero group elements or the group 18 elements.
Noble gases are odorless, colourless, monatomic gases. They are referred to as noble gases as they are quite unreactive except under some extreme conditions. Their inertness results from their completely filled valence shell. So let's get started with the characteristics of group 18 elements.
General Characteristics Of Noble Gases
Group 18 elements are known as noble or inert gases. They are called inert because they do not take part in any chemical reaction except under some extreme conditions and so we can say that they are chemically inert.
All the elements of group 18 i.e. Helium (He), Neon(Ne), Argon(Ar), Krypton(Kr), Xenon(Xe), Radon(Rn), Organesson(Og) are non-metallic elements.
The zero group is designated so because of the zero valence electrons that the elements of this group have.
Group 18 is placed in the extreme right-hand side of the long periodic table. This position is justified with the fact that each column from left to right proceeds with the addition of one valence electron in its outer shell until it gets completely filled in Group 18.
Their nature of reactivity is almost inert and serves as an intermediate bridge between the strong electronegative elements of VIIA and strong electropositive elements of IA groups in the periodic table.
All the members of the 18th group possess 8 electrons in their outermost shell except for Helium which has 2 electrons in its outermost shell.
Electronic Configuration of Zero Group Elements
Zero Group Elements | Electronic Configuration |
He | ...1s2 |
Ne | ...2s2, 2p6 |
Ar | ...3s2, 3p6 |
Kr | ...3d10, 4s2, 4p6 |
Xe | ...4d10, 5s2, 5p6 |
Rn | ...4f14, 5d10, 6s2, 6p6 |
Og | ...5f14, 6d10, 7s2, 7p6 |
Characteristics of Noble Gases
All the gases except for helium possess ns2, np6 configuration and hence the differentiating electron enters into p-subshell and thus, they are included in p-block elements.
All the noble gases except helium which has 1s2 configuration, a completely filled 1st shell have their outermost shell with a complete octet.
Their outer shell configuration is:
He: 1s2
Rest all: ns2 np6
These elements also called noble gases have no tendency to lose or gain electrons because of a completely filled outer shell or stable configuration and so usually under normal conditions do not participate in chemical reactions.
All the elements of group 18 are gases and Rn and Og are radioactive ones. These gases are also called rare gases because of their presence in very minute quantities in the atmosphere.
These gases are almost inert because of no availability of valence electrons. However, under extreme conditions, some compounds of xenon and two krypton fluorides have been synthesized.
All of them are colorless, odorless, monoatomic gases.
Conclusion
If you are keen to learn more about Group 18 Elements Characteristics, do check out the Vedantu website. You can use the information for preparing about the subject.
FAQs on Group 18 Elements Characteristics
1. What are the key physical properties that characterise the Group 18 elements?
The Group 18 elements, also known as noble gases, share several distinct physical properties. They are all:
- Monatomic: They exist as individual atoms rather than molecules.
- Colourless, Odourless, and Tasteless: Under standard conditions, they are non-reactive and do not have any sensory characteristics.
- Low Melting and Boiling Points: Due to the presence of only weak van der Waals forces of attraction between atoms, very little energy is needed to change their state from solid to liquid or liquid to gas.
- Slightly Soluble in Water: Their solubility in water is low but tends to increase down the group from Helium to Radon.
2. What is the general electronic configuration for noble gases, and why is it so important?
The general valence shell electronic configuration for Group 18 elements is ns²np⁶, with the exception of Helium, which has a configuration of 1s². This configuration is highly significant because it represents a completely filled outermost electron shell, known as a stable octet (or a duplet for Helium). This stability is the primary reason for their chemical inertness, as these elements have no tendency to lose, gain, or share electrons to form chemical bonds under normal conditions.
3. Why are the elements of Group 18 often called 'noble gases' or 'inert gases'?
These elements are called 'noble gases' because of their extremely low reactivity, similar to how nobility was considered to be above common affairs. The term 'inert gases' also refers to this lack of chemical reactivity. Their stable electronic configuration, with a completely filled valence shell, means they do not readily participate in chemical reactions. While not completely inert (as some compounds can be formed under specific conditions), their general reluctance to react is their most defining chemical characteristic.
4. Why do noble gases have very high ionisation enthalpies?
Group 18 elements exhibit the highest ionisation enthalpies in their respective periods. Ionisation enthalpy is the energy required to remove the most loosely bound electron from an atom. Due to their stable ns²np⁶ electronic configuration and high effective nuclear charge, the electrons are held very tightly by the nucleus. A large amount of energy is therefore needed to overcome these strong attractive forces and remove an electron, disrupting their stable state. This is a fundamental reason for their low chemical reactivity.
5. If noble gases are so unreactive, how is it possible for elements like Xenon to form compounds?
While noble gases are generally unreactive, it is not impossible for them to form compounds. The first true noble gas compound, xenon hexafluoroplatinate (Xe⁺[PtF₆]⁻), was synthesised by Neil Bartlett in 1962. He observed that the first ionisation enthalpy of Xenon was comparable to that of the oxygen molecule (O₂). Since he had already created a compound with O₂, he reasoned that a similar reaction could occur with Xenon. For heavier noble gases like Xenon (Xe) and Krypton (Kr), the outermost electrons are further from the nucleus and are shielded by more inner electrons. This makes their ionisation enthalpies low enough to allow them to react with highly electronegative elements like fluorine and oxygen under specific, high-energy conditions.
6. What are some important real-world applications of noble gases like Helium, Neon, and Argon?
Despite their inertness, the unique properties of noble gases make them valuable in various applications:
- Helium (He): Used in weather balloons and airships due to its low density and non-flammability. It is also used as a cryogenic agent for cooling superconducting magnets in MRI scanners and as a component in breathing mixtures for deep-sea divers.
- Neon (Ne): Famously used in advertising signs ('neon signs') which glow with a distinct reddish-orange light when an electric current passes through it. It's also used in voltage indicators and lasers.
- Argon (Ar): Provides an inert atmosphere for high-temperature metallurgical processes, such as arc welding, and for growing silicon and germanium crystals. It is also used to fill incandescent light bulbs to prevent the filament from deteriorating.
7. Why do noble gases glow with distinct colours when an electric current is passed through them?
When a high voltage electric current is passed through a noble gas at low pressure, its electrons absorb energy and get excited, jumping to higher energy levels. This excited state is unstable. The electrons quickly fall back to their original, stable energy levels. As they fall back, they release the absorbed energy in the form of light. The colour of the light emitted is unique to each element because the energy difference between the electron shells is different for each type of atom. This results in Helium glowing pink, Neon a bright reddish-orange, Argon a pale blue-lavender, and so on.
8. How do atomic size and liquefaction trends change as you move down Group 18?
As you move down Group 18 from Helium to Radon:
- Atomic Size Increases: The atomic radius increases because each successive element has an additional electron shell, placing the outermost electrons further from the nucleus.
- Ease of Liquefaction Increases: The tendency of the gas to be liquefied increases. This is because the strength of the attractive van der Waals forces increases with the size of the atom and the number of electrons. Larger atoms are more easily polarised, leading to stronger temporary dipoles and thus stronger interatomic attractions, making it easier to convert the gas into a liquid.
9. Is there a simple mnemonic to remember the names and order of the Group 18 elements?
Yes, a popular and easy mnemonic to remember the Group 18 elements—Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn)—is: "He Never Argued; Kept Xenon Quietly Running." This simple sentence helps students recall the elements in their correct order on the periodic table.
