Problem 139 - A Complete Resource Book in Chemistry for JEE Main

Question

How many of these elements are less electronegative than N-atom (No. only) F, O, C, B, Be, P, C, Si, Br

Step-by-Step Solution

Answer

6 elements (C, B, Be, P, Si, Br) are less electronegative than nitrogen.

Step 1: Understand Electronegativity

Electronegativity is the ability of an atom to attract electrons in a chemical bond. It generally increases across a period and decreases down a group in the periodic table.

Step 2: Locate Nitrogen and Other Elements

Identify the position of nitrogen (N), fluorine (F), oxygen (O), carbon (C), boron (B), beryllium (Be), phosphorus (P), silicon (Si), and bromine (Br) on the periodic table. Note that F is to the right of N while others like B, Be, P, Si, and Br are either to the left or below.

Step 3: Compare Electronegativity Values

Use a reference or table of electronegativity values. Nitrogen has an electronegativity value of 3.04 (Pauling scale). Compare it with the following values: F = 3.98, O = 3.44, C = 2.55, B = 2.04, Be = 1.57, P = 2.19, Si = 1.90, Br = 2.96.

Step 4: Identify Elements Less Electronegative than Nitrogen

Elements with lower electronegativity values than nitrogen include carbon (C), boron (B), beryllium (Be), phosphorus (P), silicon (Si), and bromine (Br).

Step 5: Count the Less Electronegative Elements

There are six elements (C, B, Be, P, Si, Br) that have lower electronegativity than nitrogen.

Key Concepts

Periodic Table Trends

Understanding periodic table trends is essential in mastering concepts around electronegativity and chemical bonding. The periodic table is organized in such a way that it helps us to predict the behavior of elements in a chemical reaction. A key trend to note is that electronegativity increases as you move from left to right across a period. This is because the nuclear charge increases, pulling the electrons more strongly and thus increasing electronegativity. On the other hand, as you move down a group, the electronegativity decreases. This occurs because the additional electron shells reduce the effective nuclear charge felt by the valence electrons, making them less strongly attracted to the nucleus. These trends help us compare elements like nitrogen (N) to other elements like fluorine (F), oxygen (O), and others, to determine which is more or less electronegative.

Chemical Bonding

Chemical bonding is the force that holds atoms together in molecules and compounds. Understanding how electronegativity influences bonding is fundamental. Electronegativity differences between atoms can predict the type of bond they will form. If the difference is large, typically greater than 1.7 on the Pauling scale, the bond tends to be ionic, meaning electrons are transferred from one atom to another. For more moderate differences, typically between 0.4 and 1.7, the bond tends to be polar covalent. In this case, electrons are shared but not equally, leading to a dipole moment. If the electronegativity difference is very small or zero, the bond is typically nonpolar covalent, with electrons shared equally. This understanding helps predict molecular behavior and interaction.

Pauling Scale

The Pauling scale is a numerical scale used to quantify the electronegativity of elements, introduced by Linus Pauling, a renowned chemist. The electronegativity values on this scale range from approximately 0.7 to 4.0. High values indicate a strong ability of an atom to attract electrons towards itself. For example, fluorine (F) has a value of 3.98, making it the most electronegative element. In comparing elements such as nitrogen (N) with a value of 3.04, and others like carbon (C) with 2.55 or boron (B) with 2.04, we can use the Pauling scale to predict and understand chemical bonding behavior. This scale helps chemists to anticipate how atoms will interact in a molecule, affecting everything from bond type to molecule polarity.