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 a favourable factor for cation formation.

Step 1: Understanding Cation Formation

Cations are positively charged ions that form when an atom loses one or more electrons. The ease of cation formation depends on how readily an atom can lose electrons.

Step 2: Analyze Factors

We need to consider each option in relation to how they affect an atom's ability to lose electrons and form a cation: - **(a) High electron affinity**: Electron affinity is the energy released when an atom gains an electron. High electron affinity suggests a tendency to gain rather than lose electrons, which is not favourable for cation formation. - **(b) High electronegativity**: Electronegativity is the ability of an atom to attract electrons in a chemical bond. High electronegativity implies that the atom holds electrons more tightly, making it less likely to lose them, which is also not favourable for cation formation. - **(c) Small atomic size**: Smaller atomic size increases nuclear charge influence over valence electrons, making them harder to remove. Hence, small atomic size is not a favourable factor for losing electrons. - **(d) Low ionization potential**: Ionization potential is the energy required to remove an electron. Low ionization potential indicates that less energy is needed to remove an electron, which facilitates cation formation.

Step 3: Determine the Favourable Factor

From the analysis, a low ionization potential is favourable for cation formation because it means an atom can lose electrons more easily.

Key Concepts

Electron Affinity

When talking about electron affinity, we refer to the energy change that occurs when an atom in the gas phase gains an electron. If an atom has a high electron affinity, it means it releases more energy upon gaining an electron.
This shows a strong tendency to gain rather than lose electrons, making it harder for such atoms to form cations. Consider chlorine, which has a high electron affinity and easily gains electrons to form negatively charged ions or anions.
For cation formation, a high electron affinity is not favorable since a cation involves losing electrons. A low electron affinity means an atom does not easily gain electrons, making it somewhat more inclined towards losing them under certain conditions, but not specifically beneficial for cation formation.

Electronegativity

Electronegativity measures how strongly an atom in a bond attracts electrons towards itself. In simpler terms, it shows an atom’s power to hold onto electrons.
High electronegativity means an atom grips its electrons tightly, making it tough to remove them. This characteristic is useful for forming stable bonds but not for cation formation.
This is because forming a cation requires the atom to lose electrons. Atoms like fluorine and oxygen are highly electronegative and are unlikely to form cations since they don’t let go of electrons easily. For metals on the other hand, electronegativity is lower, allowing them more readily to form cations.

Atomic Size

The atomic size is determined by the distance from the nucleus of an atom to the outermost electrons, or valence electrons. Smaller atoms have their electrons closer to the nucleus.
This means the nuclear charge has a stronger pull on the electrons, making it more challenging to remove them and form a cation. Thus, a small atomic size is not favorable for cation formation.
In contrast, larger atoms with more distant valence electrons can lose them more easily, as the nuclear pull is weaker. For example, alkali metals like potassium have larger atomic sizes, making them more prone to forming cations.

Ionization Potential

Ionization potential, or ionization energy, is the amount of energy required to remove an electron from an atom in the gas phase. A low ionization potential means that less energy is needed to detach an electron.
This property is crucial for cation formation because it indicates that an atom can easily lose electrons to become positively charged. Elements in the alkali metal group, like sodium, have low ionization potentials.
These elements readily lose an electron to form cations, making low ionization potential the most favorable factor for cation generation compared to other factors like electron affinity, electronegativity, or atomic size.