Problem 12 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is the atomic number of a metal? (a) 32 (b) 34 (c) 36 (d) 38

Step-by-Step Solution

Answer

The atomic number of a metal is 38 (Strontium).

Step 1: Understand Atomic Numbers and Metals

The atomic number is the number of protons in the nucleus of an atom. Metals, which are elements that typically display properties such as conductivity, ductility, and malleability, are found on the left side and in the center of the periodic table.

Step 2: Locate Atomic Numbers on the Periodic Table

Identify the elements that correspond to the given atomic numbers on the periodic table. Atomic number 32 is Germanium (Ge), number 34 is Selenium (Se), number 36 is Krypton (Kr), and number 38 is Strontium (Sr).

Step 3: Determine Which Element is a Metal

Check if the elements associated with the atomic numbers are metals. Germanium is a metalloid, Selenium is a non-metal, Krypton is a noble gas, and Strontium is an alkaline earth metal.

Step 4: Identify the Correct Answer

From the elements listed, only Strontium (Sr), with an atomic number of 38, is a metal.

Key Concepts

Periodic Table

The periodic table serves as a key tool for understanding the arrangement and properties of chemical elements. It is structured in a way that groups elements with similar properties together, helping students anticipate the behavior and characteristics of elements they study.

On the periodic table, elements are arranged by increasing atomic number. This means each element is listed by the number of protons it possesses.

Elements are placed in rows called periods and columns called groups. The location of an element in the periodic table reveals much about its reactivity and properties, including whether the element is a metal, non-metal, or metalloid. This organization becomes particularly useful when trying to determine the classification and properties of an element like Strontium.

Metals and Non-Metals

Metals and non-metals compose the majority of the elements on the periodic table. Metals are generally found on the left side and center of the table, while non-metals are located on the right.

Non-metals, such as Selenium in our exercise, have different properties compared to metals. They are poor conductors of heat and electricity and are not ductile or malleable.

Metals, like Strontium (atomic number 38), demonstrate quite different characteristics:

• Conductivity: Metals are excellent conductors of electricity and heat.
• Malleability: They can be hammered or rolled into sheets.
• Ductility: Metals can be drawn into wires without breaking.

Learning about these differences helps students understand why Strontium is classified as a metal, while others like Selenium are not.

Properties of Elements

Different elements exhibit distinct properties, which allow us to categorize them in groups like metals, non-metals, and metalloids. Understanding these properties is important for identifying how an element might react or be used in practical applications.

For instance, Strontium, a metal, is known for its reactivity and is often utilized in fireworks for its brilliant red flames when combusted. This is just one example of how specific properties aid in real-world use cases.

On the contrary, a non-metal such as Krypton, despite not being reactive, is used in lighting due to its stable characteristics. Krypton is chemically inert, making it dependable and safe for use in applications like flash photography or fluorescent bulbs. These examples showcase the importance of understanding element properties in both academic study and practical use.