Problem 11 - A Complete Resource Book in Chemistry for JEE Main

Question

The outermost configuration of the most electronegative elements is (a) \(\mathrm{ns}^{2} \mathrm{np}^{5}\) (b) \(\mathrm{ns}^{2} \mathrm{np}^{6}\) (c) \(\mathrm{ns}^{2} \mathrm{np}^{4}\) (d) \(\mathrm{ns}^{2} \mathrm{np}^{3}\)

Step-by-Step Solution

Answer

The correct answer is (a) \(\mathrm{ns}^{2} \mathrm{np}^{5}\).

Step 1: Understand Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The most electronegative elements are found in the upper right corner of the periodic table, with fluorine being the most electronegative.

Step 2: Identify Group

The most electronegative elements belong to Group 17 of the periodic table, which consists of halogens. These elements include fluorine, chlorine, bromine, iodine, and astatine.

Step 3: Determine Electron Configuration

Halogens have an electron configuration that ends in \({\mathrm{np}^{5}}\), where \({n}\) is the principal quantum number. This reflects their need to gain only one electron to achieve a stable, full outer shell with the \({ns}^{2} \, {np}^{6}\) configuration.

Step 4: Match with Options

Compare the electron configuration of halogens (\(ns^{2} np^{5}\)) with the provided options. The correct choice is the one that matches the \({ns}^{2} np^{5}\) configuration.

Key Concepts

Electronegativity

Electronegativity is a fundamental chemical property that reveals how strongly an atom can attract electrons when it forms a bond with another atom. Imagine atoms as magnets for electrons, where the strength of the magnet varies among different elements.
This concept is important in understanding how atoms interact in molecules and influences how molecules behave.

• Fluorine is the most electronegative element, which means it has a strong ability to attract electrons.
• This property helps to predict and explain chemical bonding behavior, such as which elements will more readily gain or lose electrons.

The elements found in the top right corner of the periodic table are typically more electronegative compared to others. This region excludes the noble gases, which usually do not form bonds.
Understanding electronegativity can help predict the nature of a chemical bond. For example, a significant difference in electronegativity between two atoms results in polar covalent or ionic bonds, where electrons are unevenly distributed or transferred between atoms.

Halogens

Halogens consist of the elements in Group 17 of the periodic table, including fluorine, chlorine, bromine, iodine, and astatine. These elements form one of the most chemically reactive groups. The name 'halogen' directly translates to 'salt-former', emphasizing that these elements frequently form salts when reacting with metals.
The reactivity of halogens is closely linked to their high electronegativity, particularly in fluorine and chlorine.

• They are highly reactive due to having seven electrons in their outermost shell (np ears 5 e), requiring only one additional electron to achieve a stable noble gas configuration (ns²np⁶).
• Halogens commonly participate in chemical reactions that fill or share their valence electron, making them extremely versatile in forming compounds.

Because they are keen to complete their outer shell, halogens often participate in the formation of acids, such as hydrochloric acid (HCl), when combined with hydrogen.

Periodic Table Groups

The periodic table is organized so that elements with similar properties are grouped into columns called "groups." These groups are significant because elements in the same group typically exhibit similar chemical behaviors.
Group 17, the halogens, showcases how a single column of elements can have distinct characteristics determined primarily by their electron configurations. These configurations dictate their tendency to gain electrons due to high electronegativity, leading to similar reactivities across the group.

• Each group is numbered, and the number usually indicates the number of valence electrons found in the outer shell of those elements.
• Group 17 contains elements with 7 valence electrons, following the ns²np⁵ electron configuration pattern.

This configuration influences their high reactivity, making them particularly eager to gain an extra electron to achieve full outer shells like the noble gases, which contribute to their similar chemical transformations across different reactions.