Problem 62 - A Complete Resource Book in Chemistry for JEE Main

Question

While moving down a group in the periodic table, which of the following would be true? (1) all the atoms have the same number of valence electrons (2) gram atomic volume increases (3) electronegativity decreases (4) metallic character decreases and the basic nature of their oxides decreases. Select the correct answer by using the following codes: (a) 1,2 and 3 (b) 2,3 and 4 (c) 2 and 3 (d) 1 and 3

Step-by-Step Solution

Answer

Option (a) 1, 2, and 3 is correct.

Step 1: Analyzing Option 1

When moving down a group, elements indeed have the same number of valence electrons as they belong to the same group. This is true for all elements within the same group. Therefore, statement (1) is correct.

Step 2: Understanding Option 2

Gram atomic volume increases as we move down a group because each element adds an additional electron shell, increasing the size of the atom. Therefore, statement (2) is correct.

Step 3: Examining Option 3

Electronegativity generally decreases down a group. This is due to the increase in atomic size, which means the valence shell is further from the nucleus, reducing the pull on shared electrons in a bond. Thus, statement (3) is correct.

Step 4: Evaluating Option 4

Metallic character typically increases as you move down a group, not decreases, because the atoms tend to lose electrons more easily. As a result, the basic nature of their oxides usually increases. Thus, statement (4) is incorrect.

Step 5: Choosing Correct Options

Based on the analysis: - Statements (1), (2), and (3) are correct. - Statement (4) is incorrect. Thus, the correct answer is (a) 1, 2, and 3.

Key Concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom that primarily determine how the atom will interact with other atoms. These electrons are responsible for the chemical properties of the elements. When you look at a group in the periodic table, especially the vertical columns, all elements within the same group have the same number of valence electrons. This is because these elements have similar electron configurations in their outer shell.
For example, all elements in Group 1, known as the alkali metals, have one valence electron. As a result, they tend to lose that one electron when forming compounds, which gives them similar chemical behaviours. This uniformity is the reason why elements within the same group often show similar chemical characteristics, regardless of their position in the periodic table.

Atomic Volume

Atomic volume relates to the size of an atom, which is influenced by the number of electron shells surrounding the nucleus. As you move down a group in the periodic table, the atomic volume increases. Each successive element adds an additional electron shell, making the atom larger.
This increase in atomic size has important implications:

• The larger atomic size can affect how tightly electrons are held.
• The increased distance from the nucleus can lead to differences in properties such as electronegativity and metallic character.

For instance, cesium, found at the bottom of Group 1, is larger than lithium at the top. This uptick in atomic volume is a consistent trend across the periodic table, impacting how elements react and bond with others.

Electronegativity

Electronegativity refers to an atom's ability to attract electrons towards itself when forming a chemical bond. It is an essential concept for understanding how atoms interact to form molecules.
In the periodic table, electronegativity tends to decrease as you move down a group. The reason for this trend is linked to the increasing atomic size. As atoms get bigger, the valence electrons are farther from the nucleus, reducing the nucleus's effective pull on them.
This decreased attraction results in:

• A weaker ability to attract electrons.
• Variability in bond strength and distance when forming compounds.

For example, fluorine, which is at the top of Group 17, is highly electronegative, while iodine, further down the group, is less so due to its larger atomic size.

Metallic Character

Metallic character describes an element's tendency to lose electrons and form positive ions, a characteristic feature of metals. As you go down a group in the periodic table, the metallic character generally increases.
This increase happens because, with additional electron shells, the outer electrons are less tightly bound to the nucleus and can be lost more easily.
Key features of increased metallic character include:

• Enhanced conductivity of electricity and heat.
• Lower ionization energies due to the outer electrons being more loosely held.

Additionally, the oxides formed by these metals become more basic in nature. For example, moving down Group 1 from lithium to cesium, you find that metallic properties become more pronounced, showcasing a clear change in metallic character.