Problem 29 - A Complete Resource Book in Chemistry for JEE Main

Question

An atom has electronic configuration: Is \(2 \mathrm{~s}^{2} 2 \mathrm{p}^{6} 3 \mathrm{~s}^{2}\) \(3 \mathrm{p}^{6} 3 \mathrm{~d}^{3} 4 \mathrm{~s}^{2}\), you will place it in (a) \(\mathrm{V}\) group (b) \(X V\) group (c) II group (d) III group

Step-by-Step Solution

Answer

The atom is in Group II.

Step 1: Identify the Valence Shell

The given electronic configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s². To determine the group of the atom, we need to identify electrons in the highest energy level, which is known as the valence shell. In this configuration, the highest principal quantum number is 4, specifically the 4s orbital, indicating the valence shell.

Step 2: Count Valence Electrons

For group determination, we count the electrons present in the valence shell. Here, the electrons in orbitals with the highest principal quantum number 4 are in 4sⁿ. According to the given configuration, 4s² shows there are 2 electrons in the valence shell.

Step 3: Determine Group Based on Valence Electrons

Elements in the s-block (columns IA and IIA on the periodic table) are determined by their valence electrons. Since this atom has 2 electrons in the 4s sub-shell, it belongs to Group II, the alkaline earth metals group.

Key Concepts

Valence Shell

To understand an atom's placement in the periodic table, one must first identify its valence shell. This is the outermost electron shell where the highest energy electrons reside. Identifying the valence shell is crucial because it determines the atom's chemical properties and its potential interactions with other atoms.
The valence shell is recognized by noting the highest principal quantum number ( ), which refers to the highest energy level that contains electrons. In the given electronic configuration, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s², the number 4 indicates the highest principal energy level and hence identifies the valence shell.
A firm grasp of the valence shell is pivotal for understanding an element's reactivity and placement in the periodic table. The principle of filling orbits helps ensure electrons are added to new levels, precisely forming the atom's outer shell that dictates its chemical nature.

Valence Electrons

Valence electrons are the electrons present in the outermost shell of an atom and are crucial in determining the bonding behavior and reactivity of the element. These electrons are the ones that participate in chemical reactions and form bonds with other elements.
In our specific electronic configuration, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s², the electrons in the 4s orbital, which have the highest principal quantum number, are the valence electrons. Count these electrons to discover how many partake in chemical bonding.

• For the given configuration, there are 2 valence electrons residing in the 4s sub-shell.
• The valence shell electrons are significant because they help determine the group of the element on the periodic table.

Understanding this concept allows us to predict how atoms will interact with one another, often forming the basis for chemical resilience or reactivity with other components.

Periodic Table Groups

The periodic table groups categorize elements based on their valence electron configuration, leading to similar chemical properties within each column. Recognizing which group an element belongs to can reveal much about its reactivity, typical oxidation states, and common compounds formed.
In the periodic table, elements are grouped vertically in what are called 'groups' or 'families.' These columns are either numbered or named, often reflecting the common characteristics of the elements within them.

• The atom with electronic configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s², has its valence electrons in the 4s orbital.
• This placement of 2 valence electrons puts the element in Group II, or 'IIA' group, also known as the alkaline earth metals.

Learning about periodic table groups provides insights into how elements may behave similarly and react under similar conditions, making these categorizations fundamental in understanding chemical behavior at a glance.