Problem 4 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Similarity in chemical properties of the atoms of elements in a group of the periodic table is most closely related to:(a) atomic numbers (b) atomic masses (c) number of principal energy levels (d) number of valence electrons

Step-by-Step Solution

Answer

Similarity is due to the number of valence electrons (option d).

Step 1: Understand the Concept of Groups

In the periodic table, elements in the same group are arranged in vertical columns, and these elements typically exhibit similar chemical properties. This similarity is due to a specific characteristic of the atoms within a group.

Step 2: Identify the Key Factor for Similarity

The primary reason for the similarity in chemical properties of elements within a group is the number of valence electrons. Valence electrons are the electrons in the outermost shell of an atom and are responsible for chemical bonding and reactivity.

Step 3: Evaluate Each Option

Examine each given option: - (a) Atomic numbers: Different elements have different atomic numbers. - (b) Atomic masses: These vary within a group and do not relate directly to chemical properties. - (c) Number of principal energy levels: This increases down the group but does not dictate similar properties. - (d) Number of valence electrons: Consistent within a group and dictates similar chemical behaviors.

Step 4: Choose the Correct Answer

Based on the analysis, the option that is most closely related to the similarity in chemical properties within a group of the periodic table is (d) number of valence electrons.

Key Concepts

Valence Electrons

Valence electrons are the electrons found in the outermost electron shell of an atom. These electrons play a crucial role in determining how an element will behave in a chemical reaction. Unlike electrons in inner shells, valence electrons are involved in forming bonds with other atoms.

Understanding valence electrons is vital because these directly influence an element's reactivity and its ability to bond with other elements. For instance, elements with a full outer shell of valence electrons, such as the noble gases, are generally inert and exhibit low reactivity, while those with one or two electrons short of a full shell, like the halogens, are highly reactive.

Valence electrons also justify why elements in the same group of the periodic table have similar chemical behaviors. Elements in the same column have the same number of valence electrons, leading to similarities in their ability to form certain types of bonds, such as ionic or covalent bonds. This is why sodium (Na) and potassium (K), both in Group 1, behave similarly by usually forming +1 ions.

Chemical Properties

Chemical properties of an element describe how it interacts with other substances. These properties are inherently linked to the number and arrangement of an atom's electrons, particularly the valence electrons.

When we talk about chemical properties, we're interested in reactions such as:

• How an element reacts with water.
• Its ability to oxidize (lose electrons).
• How it forms compounds with elements like oxygen or chlorine.

Elements in the same group of the periodic table often share chemical properties because they have the same number of valence electrons. For example, the alkali metals react vigorously with water, capturing the essence of their shared chemical properties within the group.

The valence electrons are key to these reactions because they can be gained, lost, or shared with other atoms in chemical reactions. Hence, knowing the valence electron configuration can help predict how an element will behave chemically.

Periodic Table Trends

Periodic table trends refer to patterns observed across the periodic table. These trends stem from the arrangement of elements according to increasing atomic number and their electron configurations.

Key trends include:

• Atomic Radius: Generally decreases from left to right across a period and increases down a group.
• Ionization Energy: Increases across a period from left to right and decreases down a group.
• Electronegativity: Tends to increase across a period and decrease down a group.

These trends are influenced by electron shell filling and the overall nuclear charge. For instance, as you move across a period left to right, electrons are added to the same energy level while protons are added to the nucleus, pulling the electron cloud closer and decreasing atomic size.

Understanding these trends can help predict how elements tend to bond chemically, their stability, and their reactivity. This predictive insight is invaluable in chemistry, aiding in the synthesis of new compounds and materials.