Class 8 General Science Notes: - Unit-6: Chemical Reaction and Bonding: Solved Exercise (Long Questions and Answers)

(National Book Foundation - New Book/New Syllabus Based on National Curriculum Pakistan 2023-2024 and Onwards)

(Class 8 General Science Notes for 8th Centralized Exam 2023-2024 and onward, FDE, Islamabad)

C. Long Questions 

Q1. Discuss the formation of ionic bonds with an example.

Ans:

Ionic Bonding: The force of attraction that holds oppositely charged ions together is called an ionic bond.

Explanation: Ionic bonds are formed between two atoms. When an atom loses electro forming Cation and the other atom gain electron to form an anion. Cation and Anion have opposite charges. They attract one another by electrostatic force.

Example: Formation of sodium chloride.

1. Sodium has only one (1) electron in its outermost shell. Chlorine has seven (7) electrons in its valence shell. It needs one electron to complete its valence shell.

2. When these two elements react, the sodium atom transferred its electron to the outer shell of a chlorine atom. After losing one electron, each sodium becomes a sodium ion (Na⁺).

3. After gaining one electron, each chlorine atom has become a chloride ion (Cl⁻).

4. These oppositely charged ions are attracted toward one another by strong electrostatic force. This type of bonding is called ionic bonding.

Electron-dot and electron–cross structure for the formation of sodium chloride:

Q2. What are covalent bonds? Discuss its types.

Ans:

Covalent Bond: The bond formed by the mutual sharing of electrons between two atoms is called a covalent bond.

Explanation: We can represent the formation of a covalent bond between two atoms using electron-cross and electron-dot symbols for the atoms and resulting molecule.

A shared pair of electrons is represented by a (-) dash in a molecule.

Types of Covalent Bond:

1. Single Covalent Bond 2. Double Covalent Bond 3. Triple Covalent

Bond

Single Covalent Bond: The sharing of one pair of electrons between two atoms is known as a Single Covalent Bond

Example: Formation of the Hydrogen molecule

A Hydrogen atom has a single valence electron. Two Hydrogen atoms share their valence electrons to form a diatomic molecule.

Double Covalent Bond: The sharing of pairs of electrons between two atoms is called a Double Covalent Bond.

Example: Formation of Oxygen molecule

Oxygen is present in group VIA, two oxygen atoms combine together to share their two pairs of electrons to form a double covalent bond. It is represented by = lines

Triple Covalent Bond: Triple covalent bond is formed by sharing of three pairs of electrons between two atoms is called Triple Covalent Bond.

Example: Formation of Nitrogen molecule

Nitrogen is present in group V, two Nitrogen atoms share their three pairs of electrons and form a triple bond. It is presented in three lines.

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Unit-5: The Periodic Table of Elements: Solved Short Questions and Answers

Class 8 General Science Notes

Source: General Science Book (National Book Foundation, Pakistan)

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