What Are the Electronic Configuration Physical Properties and Reactivity Trends of Group 18 Elements
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
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FAQs on Group 18 Elements and Their Physical and Chemical Characteristics
1. What are Group 18 elements in the periodic table?
The Group 18 elements are the noble gases—helium, neon, argon, krypton, xenon, radon, and oganesson—located in the last column of the periodic table. These elements are characterized by:
- A completely filled outermost electron shell
- Very low chemical reactivity
- Existence as monoatomic gases under standard conditions (except predicted properties of oganesson)
- High ionization energies compared to other groups
They are also known as noble gases or inert gases due to their chemical stability.
2. Why are Group 18 elements called noble gases?
Group 18 elements are called noble gases because they have a completely filled valence shell, which makes them extremely unreactive. This stable electronic configuration gives them:
- Very low tendency to gain or lose electrons
- Very high ionization energy
- Almost zero electron affinity (in most cases)
For example, neon has the stable configuration 1s2 2s2 2p6, which satisfies the octet rule, making it chemically inert under normal conditions.
3. What is the electronic configuration of Group 18 elements?
The general electronic configuration of Group 18 elements is ns2 np6, except helium which is 1s2. This means:
- The outermost shell is completely filled with electrons
- They have a stable octet (or duplet in helium)
For example, argon (Z = 18) has the configuration 1s2 2s2 2p6 3s2 3p6, which explains its chemical inertness.
4. What are the physical properties of noble gases?
The noble gases are colorless, odorless, monoatomic gases with very low boiling and melting points. Their main physical properties include:
- Exist as single atoms (monoatomic) in gaseous state
- Very weak intermolecular (London dispersion) forces
- Low densities compared to most other elements
- Increase in atomic size and density down the group
For example, helium has the lowest boiling point of all elements (about 4.2 K).
5. Why are noble gases chemically unreactive?
Noble gases are chemically unreactive because they have a completely filled valence shell, giving them maximum electronic stability. As a result:
- They do not easily gain electrons (low electron affinity)
- They do not easily lose electrons (high ionization energy)
- They have no tendency to form chemical bonds under normal conditions
However, heavier noble gases like xenon can form compounds under special conditions.
6. Do noble gases form compounds?
Yes, heavier noble gases such as xenon and krypton can form compounds under specific conditions. For example, xenon reacts with fluorine to form XeF2, XeF4, and XeF6. A balanced reaction is:
Xe(g) + F2(g) → XeF2(s)
- Occurs under controlled temperature and pressure
- Requires strong oxidizing agents like fluorine
Helium and neon do not form stable compounds under normal conditions.
7. What are the uses of Group 18 elements?
Group 18 elements are widely used due to their inertness, low reactivity, and unique physical properties. Important uses include:
- Helium: filling balloons and cryogenics
- Neon: neon advertising lamps
- Argon: inert atmosphere in welding and light bulbs
- Xenon: flash lamps and ion propulsion systems
- Radon: used in radiotherapy (limited use due to radioactivity)
Their chemical stability makes them ideal for providing inert environments.
8. How does atomic size change down Group 18?
Atomic size increases down Group 18 due to the addition of new electron shells. As you move from helium to radon:
- The number of occupied shells increases
- Shielding effect increases
- Atomic radius becomes larger
For example, helium has the smallest atomic radius, while radon has a much larger atomic size because it has more energy levels.
9. What is the trend in ionization energy of noble gases?
The ionization energy of noble gases decreases down the group. This trend occurs because:
- Atomic size increases down the group
- Outer electrons are farther from the nucleus
- Shielding effect reduces nuclear attraction
Helium has the highest ionization energy in the periodic table, while radon has a lower value compared to other noble gases.
10. What is the difference between inert gases and noble gases?
The terms inert gases and noble gases both refer to Group 18 elements, but “noble gases” is the more accurate term. This is because:
- “Inert gases” suggests they never react
- Heavier noble gases like xenon can form compounds such as XeF4
Therefore, the modern and scientifically correct term is noble gases, since they are mostly unreactive but not completely inert.
