Problem 1 - A Complete Resource Book in Chemistry for JEE Main

Question

The element with atomic number 12 belongs to ......... group and .......... period. (a) IA, third (b) IIIA third (c) IIA, third (d) IIA, second

Step-by-Step Solution

Answer

The element belongs to IIA group and third period, so option (c) is correct.

Step 1: Identify Atomic Number

The given problem states that the element has an atomic number of 12. The atomic number corresponds to the number of protons in an atom, which also helps determine its position in the periodic table.

Step 2: Locate the Element

With an atomic number of 12, we identify the element as Magnesium (Mg) in the periodic table.

Step 3: Determine the Period

Periods in the periodic table are the horizontal rows. For Magnesium (Mg), it is located in the third period because all elements from atomic number 3 to 10 are in period 2, while those from 11 to 18 are in period 3.

Step 4: Determine the Group

Groups are the vertical columns in the periodic table. Magnesium is found in the IIA group, which consists of alkaline earth metals.

Step 5: Compare Choices

The correct answer should match the period and group determined: IIA, third. This corresponds to option (c) in the provided choices.

Key Concepts

Understanding Atomic Number

The atomic number is a fundamental concept in understanding elements on the periodic table. It represents the number of protons found in the nucleus of an atom.
The atomic number is critical because it determines the identity of an element. For example, any atom with 12 protons is identified as Magnesium (Mg).

Here are some important points about atomic numbers:

• Each unique atomic number corresponds to a unique element.
• Elements in the periodic table are arranged in increasing order of their atomic numbers.
• Atomic number is also equal to the number of electrons in a neutral atom.

The atomic number not only gives the characteristic identity to each element, but also helps to locate it within the periodic table, providing a gateway to understanding its properties and behaviors.

Exploring Electron Configuration

Electron configuration is like the blueprint that shows the distribution of electrons in an atom's electron shells and subshells. Understanding electron configuration is pivotal in chemistry because it explains how atoms bond and react with one another.
The electron configuration for Magnesium (Mg), with atomic number 12, is written as: \[ 1s^2 2s^2 2p^6 3s^2 \]This configuration reveals that magnesium has two electrons in its outermost (3s) shell.

The following are key aspects of electron configuration:

• Electron configurations are written in order of increasing energy levels and subshells.
• Electrons fill the lowest available energy orbitals first from ground state, following the Aufbau principle.
• The electron configuration of an element defines its chemical properties, such as how it bonds with other elements.
• Knowing the electron configuration helps predict the position of elements in the periodic table.

Thus, a solid grasp of electron configuration is essential for understanding chemical reactions and predicting how different elements interact with each other.

Introducing Alkaline Earth Metals

Alkaline earth metals form an important group in the periodic table, known as Group IIA. These include elements like Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium.
Alkaline earth metals share several characteristics that make them crucial in both chemical theory and practical applications.
Notable characteristics of alkaline earth metals include:

• They have two electrons in their outermost s shell, giving them a characteristic electron configuration that influences their reactivity.
• These metals are shiny, silvery-white, and are relatively reactive at standard temperature and pressure.
• They readily form compounds with non-metals and are commonly found in various minerals in the Earth's crust.
• Due to their reactivity, alkaline earth metals are usually not found in their elemental form in nature.

Magnesium, specifically, is lightweight and commonly used in alloys for construction materials and automotive parts.
Understanding alkaline earth metals bridges the world of theoretical chemistry with practical applications, making it a key topic in any chemistry curriculum.