Problem 122 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: List I 1\. most electronegative 2\. most electron affinity 3\. liquid halogen 4\. radio active halogen List II (i) \(\mathrm{I}_{2}\) (ii) At (iii) \(\mathrm{F}_{2}\) (iv) \(\mathrm{Cl}_{2}\) (v) \(\mathrm{Br}_{2}\)

Step-by-Step Solution

Answer

1 – iii, 2 – iv, 3 – v, 4 – ii

Step 1: Understanding Electronegativity

Electronegativity is the ability of an atom to attract electrons towards itself. Among the elements, fluorine \((\mathrm{F})\) is known as the most electronegative element.

Step 2: Identifying Electron Affinity

Electron affinity refers to the energy change when an electron is added to a neutral atom. Chlorine \((\mathrm{Cl}_{2})\) is known to have the highest electron affinity among the halogens.

Step 3: Determining the Liquid Halogen

At room temperature, bromine \((\mathrm{Br}_{2})\) is the only halogen found in liquid state.

Step 4: Finding the Radioactive Halogen

Astatine \((\mathrm{At})\) is a halogen and is known to be radioactive.

Key Concepts

Electronegativity

Electronegativity is a fundamental concept in chemistry that helps us understand how atoms interact in molecules. It measures an atom's ability to attract and hold onto electrons when it's part of a compound. The concept was introduced by Linus Pauling, who assigned electronegativity values to elements based on their chemical behavior and bond energies.

Fluorine ( \(\mathrm{F}\)) is the most electronegative element on the periodic table. This means that when fluorine forms a bond with another atom, it pulls the bonded electrons towards itself more strongly than any other element. This is why fluorine often forms polar covalent bonds where it holds a partial negative charge. Understanding electronegativity helps predict how atoms will bond and the properties of the resulting molecules.

• Electronegativity values increase across a period (from left to right) and decrease down a group (from top to bottom) in the periodic table.
• Higher electronegativity indicates a stronger ability to attract electrons.

Electron Affinity

Electron affinity refers to the energy change that occurs when an atom in the gaseous state accepts an electron. It's a measure of how much an atom "wants" to gain an electron and become negatively charged. When an electron is added, energy can either be released (exothermic) or absorbed (endothermic), but for most non-metals, the process is exothermic and releases energy.

Among the halogens, chlorine ( \(\mathrm{Cl}_2\)) has the highest electron affinity. This means that when chlorine gains an electron to form chloride ions, it releases a significant amount of energy. This makes it quite reactive, especially with metals, forming compounds like sodium chloride. The high electron affinity of chlorine contributes to its powerful oxidizing properties.

• Electron affinity values can indicate how likely an atom is to form negative ions.
• Halogens generally have high electron affinities, making them act as strong oxidizing agents.

Halogens

Halogens are a group of non-metals in Group 17 of the periodic table. This group includes fluorine ( \(\mathrm{F}\)), chlorine ( \(\mathrm{Cl}_2\)), bromine ( \(\mathrm{Br}_2\)), iodine ( \(\mathrm{I}_2\)), and astatine ( \(\mathrm{At}\)). Halogens are known for their high reactivity, as they strive to gain an extra electron to fill their outer electron shells.

Their reactivity decreases down the group, with fluorine being the most reactive and astatine the least. At room temperature, bromine is unique among the halogens as it is in a liquid state, while fluorine and chlorine are gases, and iodine and astatine are solids. Astatine is also unique because it is radioactive, which means it spontaneously decomposes, releasing radiation energy.

• Halogens form salts when they react with metals, like sodium chloride from chlorine and sodium.
• Their reactivity and physical states are important for various industrial applications and natural processes.