Problem 8 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The statements that are true for the long form of the periodic table are: [1988 - 1 Mark] (a) it reflects the sequence of filling the electrons in the order of subenergy level \(\mathrm{s}, \mathrm{p}, \mathrm{d}\) and \(\mathrm{f}\). (b) it helps to predict the stable valency states of the elements (c) it reflects trends in physical and chemical properties of the elements (d) it helps to predict the relative ionicity of the bond between any two elements.

Step-by-Step Solution

Answer

The true statements are (a), (b), and (c).

Step 1: Understanding the Long Form of the Periodic Table

The long form of the periodic table is designed so elements are arranged in increasing atomic number, allowing us to see the pattern of electron configurations which reflects the sequence of filling subenergy levels (s, p, d, f). This supports option (a).

Step 2: Predicting Stable Valency States

The periodic table helps predict the stable valency of elements based on their group numbers. Elements tend to gain, lose, or share electrons to achieve the valency similar to the nearest noble gas configuration, supporting option (b).

Step 3: Identifying Trends in Properties

The periodic table shows trends in physical and chemical properties such as electronegativity, ionization energy, and atomic radius as you move across periods or down groups, which supports option (c).

Step 4: Predicting Ionicity of Bonds

While the periodic table can provide insights into the types of bonds formed by elements and trends in electronegativity, it doesn't directly predict the relative ionicity of bonds. Therefore, option (d) is not a straightforward truth related to the periodic table's design.

Key Concepts

Electron Configuration

Electron configuration is the arrangement of electrons around the nucleus of an atom, which is pivotal in determining how atoms interact with each other. Each atom’s electrons occupy specific energy levels, known as shells and subshells, denoted by the letters s, p, d, and f. As we move through the periodic table from left to right and top to bottom, electrons are filled into these subshells in a specific order known as the Aufbau principle.

Understanding electron configuration helps explain why elements are placed where they are on the periodic table. For instance, all noble gases have complete outer shells, which makes them particularly stable. The unique electron configuration of each element dictates its chemical behavior and reactivity. For chemistry enthusiasts or students, grasping this concept unravels the mysteries of chemical bonding and elemental properties.

Valency Prediction

Valency, the combining capacity of an element, is a crucial concept that helps us understand how elements interact to form compounds. The valency of an element typically correlates with the number of electrons an atom needs to lose, gain, or share to fulfill the octet rule, aiming for a full outer electron shell.

The periodic table is a powerful tool for predicting valency. Elements in the same group (vertical columns) often have similar valencies. For example, alkali metals in group 1 typically have a valency of +1 because they have one electron in their outermost shell which they lose to achieve noble gas configuration. On the other hand, elements in group 17 have a valency of -1 as they gain an electron to complete their outer shell. This uniformity in the periodic table facilitates the understanding of chemical bonding patterns.

Understanding valency not only aids in predicting how elements combine but also enhances our comprehension of the structure and properties of compounds formed.

Trends in Chemical Properties

The periodic table is a map that reveals trends in physical and chemical properties of elements as we navigate across the rows (periods) or downturn the columns (groups). Recognizing these trends is essential in predicting and explaining the behavior of elements.

Some notable trends include:

• Electronegativity: This refers to an element's ability to attract and hold onto electrons. It generally increases across a period and decreases down a group.
• Ionization Energy: This is the energy needed to remove an electron from an atom. Similar to electronegativity, it increases across a period and decreases down a group.
• Atomic Radius: This is the size of an atom. As you move across a period, the atomic radius usually decreases due to an increase in nuclear charge, pulling electrons closer. However, as you move down a group, the atomic radius increases because of additional electron shells.

These patterns help scientists predict how elements will react chemically, making the periodic table an invaluable resource for chemists and researchers alike.

Long Form Periodic Table

The long form periodic table is designed to present the elements in a way that enhances our understanding of the periodic law—the principle that the properties of elements are periodic functions of their atomic numbers. In this layout, elements are organized by increasing atomic number, allowing easy identification of the sequence in which electrons fill subshells (s, p, d, and f).

This arrangement is beneficial in several ways:

• It illustrates the complete cycles of electron configuration, making it simpler to identify element groups such as transition metals, which have partially filled d subshells.
• By providing a clear understanding of the sequence of electron filling, it facilitates the prediction of chemical reactivity and bonding behavior based on electron arrangement.
• The long form also enables easier teaching and visualization of periodic trends, including metallic and non-metallic character, which follow particular patterns across the table.

In essence, the long form periodic table is not only a tool for classification and predicting element behavior but also a gateway to understanding the underlying principles that govern chemical interactions.