Problem 2 - A Complete Resource Book in Chemistry for JEE Main

Question

An element having atomic number 56 belongs to (a) lanthanides (b) actinides (c) alkaline earth metals (d) none of these

Step-by-Step Solution

Answer

The element with atomic number 56 belongs to the alkaline earth metals (c).

Step 1: Identify the Element

The atomic number 56 corresponds to the element barium (Ba) on the periodic table.

Step 2: Determine the Group

Barium (Ba) belongs to Group 2 of the periodic table, which is known as the alkaline earth metals group.

Step 3: Classify the Element

Since barium is in Group 2, it is classified as an alkaline earth metal. The options given in the question are: lanthanides, actinides, alkaline earth metals, and none of these.

Step 4: Match with Options

According to the classification, barium is an alkaline earth metal. Thus, it matches option (c).

Key Concepts

Atomic Number

The atomic number of an element is a fundamental property that defines the number of protons found in the nucleus of an atom of that element. Every element in the periodic table is assigned a unique atomic number, which in turn helps to identify and differentiate it from other elements. The atomic number determines not only the identity of the element but also its position in the periodic table.
For example, an atomic number of 1 corresponds to hydrogen, while the atomic number 56, which is our focus here, corresponds to barium (Ba). The atomic number is often represented as a subscript on the left side of the element's symbol, for example, in barium, it is written as \( _{56} \text{Ba} \). Understanding the atomic number facilitates the prediction of an element's chemical behavior and its relationship with other elements in the periodic table.

Group Classification

In the periodic table, elements are arranged in columns known as groups. Each group consists of elements that have similar valence electron configurations, which tend to result in similar chemical properties. Group classification helps in organizing the vast amount of chemical information about elements in a way that is easy to understand and predict.
There are 18 groups in the periodic table, and these groups are often labeled from 1 to 18. Elements in Group 1 are known as alkali metals, Group 2 contains alkaline earth metals, and so on. Barium (Ba), specifically, belongs to Group 2. This classification places it among the alkaline earth metals, a group known for having two electrons in their outermost electron shell, which leads to specific trends in their reactivity and physical properties.

Alkaline Earth Metals

Alkaline earth metals form an essential part of the periodic table. This group consists of six elements: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). These elements are located in Group 2 of the periodic table and share common characteristics.
Some general properties of alkaline earth metals include:

• Having two electrons in their outermost shell, which they easily lose to form cations with a charge of +2.
• Being shiny and somewhat reactive, although they are less reactive than alkali metals (Group 1).
• Showing increasing reactivity and decreasing melting points as you move down the group from beryllium to radium.

Each element in the alkaline earth metals group shares this foundational chemistry but has unique properties that become more apparent in specific reactions and uses.