Problem 23 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is a favourable factor for cation formation? (a) high electron affinity (b) high electronegativity (c) small atomic size (d) low ionization potential

Step-by-Step Solution

Answer

Low ionization potential is favorable for cation formation.

Step 1: Understand the Question

The question is asking which factor is favorable, or supports, the formation of a cation. A cation is a positively charged ion formed when an atom loses one or more electrons.

Step 2: Define the Terms

Let's define key terms: - Electron affinity is the tendency of an atom to accept an electron. - Electronegativity is the ability of an atom to attract electrons towards itself. - Atomic size refers to the size of an atom, which can affect how tightly its electrons are held. - Ionization potential is the energy required to remove an electron from an atom, forming a cation.

Step 3: Analyze Each Option

Go through each option to understand how it relates to cation formation: - (a) High electron affinity: Atoms don't favor losing electrons with high electron affinity. They prefer gaining electrons to form anions. - (b) High electronegativity: Atoms with high electronegativity attract electrons rather than losing them. - (c) Small atomic size: Atoms with small sizes hold their electrons tightly, making it harder to lose them. - (d) Low ionization potential: Lower ionization potential means less energy is required to remove an electron, making cation formation easier.

Step 4: Choose the Correct Option

Option (d), low ionization potential, is favorable for cation formation because it means less energy is needed for the atom to lose an electron and form a cation.

Key Concepts

Ionization Potential

Ionization potential, also known as ionization energy, is a crucial concept in chemistry. It refers to the amount of energy required to remove an electron from an isolated atom in its gaseous state. This process results in the formation of a cation, which is a positively charged ion.

Here's why this matters:

• A low ionization potential means that less energy is necessary to remove an electron, which facilitates easier cation formation.
• Elements with a high ionization potential tightly hold their electrons, making it challenging to lose them and form cations.

Ionization potential varies across the periodic table. Elements on the right side tend to have higher ionization energies because they have more protons attracting electrons closely. However, elements on the left have a lower ionization potential, making them more likely to form cations.

Electron Affinity

Electron affinity describes an atom's ability to gain an electron and release energy in the process. When an atom gains an electron, it forms an anion, which has a negative charge.

This might seem opposite to cation formation but is an important concept to grasp:

• High electron affinity indicates an atom strongly desires to gain an electron.
• Atoms with high electron affinities are typically non-metals.
• These atoms are less likely to lose electrons to form cations. Instead, they gain electrons to form anions.

For example, halogens like fluorine and chlorine have very high electron affinities because they want to achieve a stable electron configuration similar to noble gases. This means high electron affinity is generally unfavorable for cation formation.

Electronegativity

Electronegativity measures how strongly an atom can attract bonding electrons towards itself. It is a key factor in explaining the behavior of atoms within molecules.

Some points about electronegativity include:

• High electronegativity means strong attraction for electrons, making it difficult for an atom to form a cation by losing electrons.
• This property is particularly evident in elements like oxygen and nitrogen which strongly pull electrons in covalent bonds.
• Typically, elements with high electronegativity are found in the top right of the periodic table, excluding noble gases.

Since high electronegativity indicates a tendency to attract electrons rather than lose them, it is not favorable for cation formation.

Atomic Size

Atomic size refers to the size of an atom, primarily determined by the radius of its electron cloud. This factor influences how easily an atom can lose or retain electrons, impacting cation formation.

Understand atomic size with these insights:

• Smaller atomic sizes usually mean electrons are held closer to the nucleus, which fosters a strong hold on electrons.
• Larger atomic sizes, often found towards the bottom of the periodic table, tend to have loosely held outer electrons.
• This loose hold in larger atoms means electrons can be removed more easily, facilitating cation formation.

Therefore, a large atomic size often means a higher likelihood of losing electrons to form cations, while a small atomic size does the opposite.