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 with atomic number 12 belongs to group IIA and third period, thus the answer is (c) IIA, third.

Step 1: Understanding Atomic Number

The atomic number of an element is the number of protons in the nucleus of an atom of that element. For the element in question, the atomic number is 12.

Step 2: Identifying the Element

Using the periodic table, find the element with atomic number 12. This element is Magnesium (Mg).

Step 3: Determine the Group

In the periodic table, elements in the same group have similar properties. Magnesium (Mg), with atomic number 12, is in Group IIA (also called Group 2). This is known as the alkaline earth metals group.

Step 4: Determine the Period

A period in the periodic table is the horizontal row of elements. Magnesium (Mg) is located in the third period of the periodic table.

Key Concepts

Atomic Number

The atomic number is a fundamental property of an element. It represents the number of protons in the nucleus of an atom and uniquely identifies each chemical element. For example, the atomic number of Magnesium is 12. This means a magnesium atom has 12 protons in its nucleus.
Knowing the atomic number is crucial because it determines the element's place on the periodic table. The chemical characteristics of an element are closely related to its atomic number, as this influences the electronic configuration and, subsequently, the element’s reactivity.
When trying to identify an element, the atomic number is the first piece of information you will need to consider. By matching the atomic number with the periodic table, you can ascertain the element’s identity. This foundational concept is key when discussing or comparing the periodic table.

Groups in Periodic Table

The periodic table is organized into groups and periods. A group is a vertical column in the table. Each group contains elements with similar chemical properties due to their similar valence electron configurations.
Magnesium, with an atomic number of 12, falls into Group IIA, also referred to as Group 2. This group is known as the alkaline earth metals. Here are some characteristics of Group IIA elements:

• They have two electrons in their outermost shell.
• They tend to lose these electrons to form +2 cations.
• They are less reactive than Group IA elements (alkali metals) but still quite reactive.
• Typically, these metals are shiny and conduct electricity well.

Understanding where an element resides in a group is essential for predicting its reactivity and its typical compounds.

Periods in Periodic Table

Periods in the periodic table are the horizontal rows. Each period signifies the number of electron shells that are occupied in the atoms of the elements. This arrangement explains how properties of elements change gradually as you move from left to right across the table.
Magnesium, a well-known metal used in various alloys, is located in the third period of the periodic table. This indicates that magnesium atoms have three electron shells. Each subsequent element in the same period has one more proton and one more electron than the element before it.
Being in the third period signifies that magnesium's electron configuration expands to three shells, which significantly influences its chemical behavior. The concept of periods is significant as it helps us understand the shared and curved properties of elements across the table.