Problem 33 - A Complete Resource Book in Chemistry for JEE Main

Question

The atomic number of an element is 17 . The number of orbitals electron pairs in its valence shell is (a) 3 (b) 4 (c) 6 (d) 8

Step-by-Step Solution

Answer

(a) 3

Step 1: Determine the Element

The atomic number, 17, corresponds to the element Chlorine on the periodic table.

Step 2: Find the Electron Configuration

Chlorine, with an atomic number of 17, has an electron configuration of \(1s^2 2s^2 2p^6 3s^2 3p^5\). This means it has 7 electrons in its outermost shell (3rd shell).

Step 3: Determine the Valence Shell

The 3rd energy level, which contains the orbitals 3s and 3p, is the valence shell for Chlorine.

Step 4: Identify the Number of Orbitals in the Valence Shell

The valence shell configuration, \(3s^2 3p^5\), indicates one filled \(s\) orbital and three \(p\) orbitals. Electrons will pair up in these orbitals.

Step 5: Calculate the Number of Electron Pairs

In the 3s orbital, there are 2 electrons forming one pair. In the 3p orbitals, with a total of 5 electrons, 2 of the orbitals will have one pair each (4 electrons), and the remaining orbital will have a single electron. Hence, there are 3 pairs of electrons in the valence shell.

Key Concepts

Valence Shell

The valence shell is a term used to describe the outermost shell of an atom that contains electrons. This shell plays a vital role in chemical reactions and bonding. Valence electrons in the valence shell determine how an atom interacts with other atoms. These electrons can be gained, lost, or shared to form chemical bonds.
Here's what you need to know about valence shells:

• They consist of the highest energy level occupied by electrons.
• They contain the electrons crucial for forming bonds with other elements.
• For Chlorine, the third shell (3s and 3p orbitals) acts as the valence shell.

Understanding the valence shell is essential because it allows you to determine the chemical reactivity and the bonding potential of elements like Chlorine.

Atomic Number

The atomic number is a unique identifier for each element on the periodic table. It indicates the number of protons found in an atom's nucleus and also corresponds to the number of electrons in a neutral atom. For Chlorine, the atomic number is 17. This means:

• There are 17 protons in the nucleus.
• There are 17 electrons surrounding the nucleus, organized into electron shells.
• The atomic number helps define the element's position on the periodic table.

Understanding the atomic number is crucial because it helps in identifying the element and determining its electron configuration, which is key to understanding its chemical properties.

Chlorine

Chlorine is a chemical element with the symbol Cl and an atomic number of 17. It is part of the halogen group and is known for its reactivity and distinct properties. Here's what you should know about Chlorine:

• It is a non-metal and a highly reactive element.
• In its natural state, it is most commonly found as a greenish-yellow gas.
• Chlorine's electron configuration is important in determining its reactivity: \(1s^2 2s^2 2p^6 3s^2 3p^5\).

Chlorine's high reactivity makes it crucial in various industrial processes and as a disinfectant in water treatment.

Orbitals

Orbitals are regions within an atom where electrons are most likely to be found. They play a fundamental role in determining an atom's electron configuration and chemical behavior. In Chlorine:

• Electrons are found in different types of orbitals: s, p, d, and f.
• Each orbital can hold a specific number of electrons: 2 for s, 6 for p, 10 for d, and 14 for f.
• The sequence of orbitals occupied by Chlorine is \(1s^2 2s^2 2p^6 3s^2 3p^5\).
• This configuration shows that the 3s and 3p orbitals make up the valence shell for Chlorine.

Understanding orbitals helps in predicting how atoms interact, form molecules, and participate in chemical reactions.