Problem 141 - A Complete Resource Book in Chemistry for JEE Main

Question

According to the periodic law of elements, the variation in properties of elements is related to their (a) atomic masses (b) nuclear masses (c) atomic numbers (d) nuclear neutron-proton number ratios

Step-by-Step Solution

Answer

(c) Atomic numbers determine the variation in properties according to the periodic law.

Step 1: Understand the Periodic Law

The periodic law states that the properties of elements are a periodic function of their atomic numbers. Atomic number refers to the number of protons in the nucleus of an atom and determines the element's position in the periodic table.

Step 2: Analyze Each Option

- Option (a): Atomic masses influence some properties, like density, but do not solely determine periodic patterns. - Option (b): Nuclear masses include both protons and neutrons, similar reasoning applies as to atomic masses. - Option (c): Atomic numbers determine the order of elements in the periodic table, influencing periodic trends directly. - Option (d): Nuclear neutron-proton number ratios affect stability and isotopes, but not primarily the organization of periodic table trends.

Step 3: Select the Correct Answer

Based on the definition of the periodic law, the periodic properties of elements are related to their atomic numbers. Hence, option (c) is the correct answer.

Key Concepts

Atomic Number

The atomic number of an element is crucial for understanding its identity and properties. It represents the number of protons in the nucleus of an atom. The atomic number uniquely identifies a chemical element and determines an atom's position on the periodic table. For example, hydrogen has an atomic number of 1 because it has one proton in its nucleus, while helium has an atomic number of 2 because it contains two protons. Understanding atomic numbers helps in several key ways:

• It dictates the chemical behavior of the element. The number of protons (and thus the number of electrons in a neutral atom) influences how an element reacts chemically.
• It determines the sequence of elements in the periodic table. Elements are arranged in order of increasing atomic number.
• It differentiates one element from another. Even if two elements have similar atomic masses, their different atomic numbers confirm that they are distinct elements.

Recognizing the atomic number's role helps to comprehend the organization and trends of the periodic table.

Periodic Table

The periodic table is a systematic arrangement of chemical elements, presented in a tabular format which is organized by increasing atomic number. Each element on the periodic table is placed in a specific location due to:

• Atomic Number: As mentioned earlier, this is the number of protons in an element. The table's organization reflects this sequential increase.
• Groups: Vertical columns in the periodic table, known as groups, have elements with similar chemical properties. This is largely because they have the same number of electrons in their outer shell.
• Periods: Horizontal rows are called periods. Properties of elements change predictably across a period.

Through the periodic table, chemists can predict the properties and behaviors of elements. This comprehensive structure enables scientists to understand the periodic trends, such as electronegativity, ionization energy, and atomic radius, which change in a predictable pattern across periods and groups.

Chemical Properties of Elements

Chemical properties of elements refer to how an element reacts or interacts with other substances, influencing how compounds form and chemical reactions occur. Several factors affect an element's chemical properties:

• Valence Electrons: Elements with similar numbers of valence electrons behave in similar ways. These electrons are key to chemical bonding.
• Atomic Radius: The size of an atom can influence its reactivity. Smaller atoms tend to attract electrons more strongly in bonds.
• Ionization Energy: The energy required to remove an electron from an atom. Higher ionization energies typically mean less reactivity.
• Electronegativity: This indicates how strongly an atom can attract and hold onto electrons.

Understanding these factors helps in predicting how elements will behave in different chemical situations. This knowledge is essential for everything from forming new materials to understanding metabolic processes in biology.