Problem 68 - A Complete Resource Book in Chemistry for JEE Main

Question

Noble gases are a group of elements which exhibit very (a) high chemical activity (b) less diamagnetic property (c) high electronegativity (d) low chemical activity

Step-by-Step Solution

Answer

Option (d) - low chemical activity.

Step 1: Understanding Noble Gases

Noble gases are a group of elements located in Group 18 of the periodic table. They include helium, neon, argon, krypton, xenon, and radon. These gases are characterized by having a complete valence electron shell, which makes them stable and less reactive.

Step 2: Identifying Properties of Noble Gases

Due to their complete valence electron shells, noble gases have very little tendency to accept additional electrons or participate in chemical reactions. This property indicates low chemical activity.

Step 3: Evaluating Options Given

Read through the provided options: (a) high chemical activity, (b) less diamagnetic property, (c) high electronegativity, and (d) low chemical activity. Compare these with what is known about noble gases.

Step 4: Choosing the Correct Option

Since noble gases have low chemical reactivity due to their complete valence electron shells, the correct answer is the one that reflects this property. Hence, the answer is (d) low chemical activity.

Key Concepts

Group 18 Elements

The noble gases are found in Group 18 of the periodic table. This group is composed of the elements helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). These gases are unique because of their inert nature, meaning they do not readily form compounds with other elements. This is why they are often called "rare gases" or "inert gases."
Noble gases are colorless, odorless, tasteless, and non-flammable, making them quite distinct from other elements in the periodic table. Despite their rarified properties, they are quite abundant in the universe. For example, helium is the second most abundant element in the universe, following hydrogen. On Earth, however, these gases are found in smaller quantities, and argon is the most abundant in the Earth's atmosphere.
Owing to their non-reactivity, noble gases are often used in various practical applications. Neon lights are a common example, as well as helium being used in balloons and cryogenics. Their inertness makes them ideal for environments where chemical reactions are undesirable.

Valence Electron Shell

The valence electron shell is the outermost shell of an atom's electron cloud, and it plays a critical role in chemical bonding and reactions. For noble gases, this outermost shell is completely filled, which is a key reason behind their stability.
Each noble gas possesses a full valence electron shell, contributing to their lack of chemical reactivity. For instance:

• Helium has two electrons filling its only shell, making it complete.
• Neon, with ten electrons, has a full outer shell of eight electrons.
• Argon also follows, having eighteen electrons with a full outer shell.

This complete electron configuration makes noble gases energetically satisfied and unlikely to participate in chemical reactions. They do not seek to gain, lose, or share electrons, which is why they are so stable and non-reactive.
The complete valence electron shell is a defining characteristic of all noble gases, setting them apart from other groups in the periodic table.

Chemical Reactivity

Chemical reactivity refers to the tendency of a substance to engage in chemical reactions, either on its own or with other substances. Noble gases are well-known for their negligible chemical reactivity. This low reactivity is a direct consequence of their full valence electron shells, which makes them highly stable.
Since these elements have complete outer shells, they have no inclination to accept additional electrons. Unlike other atoms that strive to achieve a stable electron configuration through chemical reactions, noble gases already possess this naturally.

• Their stable electron configuration repels the need for typical chemical bonding.
• This results in the lowest chemical potential among the elements.

The non-reactive nature of noble gases means they rarely take part in reactions to form compounds. When compounds of noble gases are formed, it is usually under extreme conditions or with elements that can force such a reaction.
Noble gases, because of their chemical inertness, are used in applications where reactivity must be minimized, such as in light bulbs and inert gas shields for welding. This characteristic makes them not only chemically fascinating but also practically invaluable.