Problem 141 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following pairs is/are correctly matched here: (a) The strongest oxidizing agent - Iodine (b) The most reactive halogen - Fluorine (c) A halogen which is liquid at room temperature-Bromine (d) The most electronegative element-Fluorine

Step-by-Step Solution

Answer

Pairs (b), (c), and (d) are correctly matched.

Step 1: Identify Characteristics of Oxidizing Agents

An oxidizing agent is a substance that gains electrons in a chemical reaction. The strongest oxidizing agents are fluorine, chlorine, bromine, and then iodine, in decreasing order of strength.

Step 2: Evaluate the Most Reactive Halogen

Reactivity in halogens decreases as you move down the group in the periodic table. Therefore, fluorine is the most reactive halogen, followed by chlorine, bromine, and iodine.

Step 3: Determine the State of Matter of Halogens at Room Temperature

At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid.

Step 4: Identify the Most Electronegative Element

Electronegativity measures an atom's ability to attract and bond with electrons. Fluorine is the most electronegative element in the periodic table.

Key Concepts

Oxidizing Agents

An oxidizing agent is a substance that accepts electrons from another species during a chemical reaction, thereby getting reduced itself. The halogens — fluorine, chlorine, bromine, and iodine — are well-known examples of strong oxidizing agents. The strength of these agents depends largely on their ability to attract electrons.

Fluorine stands out as the strongest oxidizing agent among the halogens due to its high electronegativity and small atomic size. It can pull electrons away from almost any other element. As we move from fluorine down to iodine in the periodic table, the oxidizing ability decreases. This is because the atoms become larger, and the outer electrons are less tightly held by the nucleus, making it harder for them to attract additional electrons.

• Fluorine: strongest oxidizing agent
• Chlorine: strong oxidizing agent
• Bromine: moderate oxidizing agent
• Iodine: weakest oxidizing agent among the halogens

Reactivity of Halogens

Halogens are highly reactive nonmetals, and their reactivity varies as you move down the group in the periodic table. Fluorine, being at the top of the group, is the most reactive of all the halogens. This high reactivity is mainly due to its high electronegativity and small atomic radius, which facilitates easy electron attraction.

As you descend the group from fluorine to iodine, reactivity decreases. The reasons include increasing atomic size and a reduction in electronegativity, which hinder the ability to attract electrons as effectively as fluorine. Hence, the order of halogen reactivity is as follows:

• Fluorine: most reactive
• Chlorine: highly reactive
• Bromine: moderately reactive
• Iodine: least reactive among the halogens

Electronegativity in Periodic Table

Electronegativity is a property that denotes the tendency of an atom to attract a shared pair of electrons towards itself in a covalent bond. Among all the elements in the periodic table, fluorine is known to be the most electronegative. With an electronegativity value of about 4.0 on the Pauling scale, fluorine's high value is attributed to its small atomic size and high effective nuclear charge.

Electronegativity generally increases across a period (left to right) and decreases down a group (top to bottom) in the periodic table. This is why fluorine, located at the top right of the periodic table (excluding noble gases), exhibits the highest electronegativity. Because of this, fluorine is adept at forming bonds with other elements, effectively pulling tighter on the bonding electrons. This creates polar bonds seen in many compounds containing fluorine.

In summary:

• Fluorine: highest electronegativity
• Electronegativity increases across a period
• Electronegativity decreases down a group

States of Matter at Room Temperature

Halogens appear in different states of matter at room temperature (approximately 25°C or 77°F) due to varying molecular interactions and atomic sizes. Fluorine and chlorine exist as gases because their molecules have weak van der Waals forces and are more dynamic in gaseous form.

Bromine is unique among the halogens; it is a red-brown liquid at room temperature. This is a result of its moderate molecular size and stronger intermolecular forces compared to the lighter halogens, causing it to condense into liquid form. Iodine, being the heaviest of the common halogens, appears as a dense solid at room temperature. It exhibits crystalline formation due to strong van der Waals forces.

To summarize the states of matter for halogens at room temperature:

• Fluorine: gas
• Chlorine: gas
• Bromine: liquid
• Iodine: solid