Unit 4: Structure of Molecules

What is the Structure of Molecules?

The Structure of Molecules explores how atoms combine to form molecules and the arrangement of these atoms within the molecules. This unit covers the principles of molecular geometry, bonding theories, and the types of molecular structures that influence the physical and chemical properties of substances. Students learn about covalent bonding, molecular shapes, and the impact of molecular structure on reactivity and interactions.

Key Topics in the Structure of Molecules:

• Molecular Geometry: Understanding the 3D arrangement of atoms within a molecule and the impact of bond angles on molecular shape.
• Bonding Theories: Exploring covalent bonding, including concepts such as sigma and pi bonds, and valence bond theory.
• Lewis Structures: Drawing and interpreting Lewis structures to represent molecule formation and electron sharing.
• VSEPR Theory: Applying the Valence Shell Electron Pair Repulsion (VSEPR) theory to predict molecular shapes and bond angles.
• Molecular Polarity: Examining how the arrangement of atoms affects the polarity of a molecule and its intermolecular forces.

Benefits of Studying the Structure of Molecules:

• Chemical Understanding: Provides insights into how molecules interact, react, and form different substances.
• Predictive Skills: Enhances the ability to predict molecular shapes, bond angles, and properties based on molecular structure.
• Advanced Knowledge: Builds a foundation for studying complex reactions, synthesis, and material science.

This unit is crucial for students to understand how molecules are structured and how these structures determine the behavior and properties of substances. Mastery of molecular structure is essential for success in advanced Chemistry topics and applications.

1. Atoms react with each other because:

a. They are attracted to each other.
b. They are short of electrons
c. They want to attain stability
d. They want to disperse

2. An atom having six electrons in its valence shell will achieve noble gas
electronic configuration by:

a. Gaining one electron
b. Gaining two electrons
c. Losing two electron
d. Losing all electrons

3. Considering the electronic configuration of atoms which atom with
the given atomic number will be the most stable one?

a. 6
b. 8
c. 10
d. 12

4. Octet rule is:

a. Description of eight electrons
b. Picture of electronic configuration
c. Pattern of electronic configuration
d. Attaining of eight electrons

5. Transfer of electrons between atoms results in:

a. Metallic bonding
b. Ionic bonding
c. Covalent bonding
d. Coordinate covalent bonding

6. When an electronegative element combines with an electropositive
element the type of bonding is:

a. Covalent
b. Ionic
c. Polar Covalent
d. Coordinate Covalent

7. A bond formed between two non-metals is expected to be:

a. Ionic
b. Covalent
c. Metallic
d. Coordinate covalent

8. A bond pair in covalent molecules usually has:

a. One electron
b. Two electrons
c. Three electrons
d. Four electrons

9. Which of the following compounds is not directional in its bonding?

a. CH₄
b. KBr
c. CO₂
d. H₂O

10. Ice floats on water because:

a. Ice is denser than water
b. Ice is crystalline in nature
c. Water is denser than ice
d. Water molecules move randomly

11. Covalent bond involves the

a. Donation of electrons
b. Acceptance of electrons
c. Sharing of electrons
d. Repulsion of electrons

12. How many covalent bonds does C₂H₄ molecule have?

a. Two
b. Three
c. Four
d. Five

13. Triple covalent bond involves how many electrons?

a. Eight
b. Six
c. Four
d. Only three

14. Which pair of the molecules has same type of covalent bonds?

a. O₂ and HCl
b. O₂ and N₂
c. O₂ and C₂H₄
d. O₂ and C₂H₂

15. Identify the compound which is not soluble in water

a. C₆H₆
b. NaCl
c. KBr
d. MgCl₂

16. Which one of the following is an electron deficient molecule?

a. NH₃
b. N₂
c. BF₃
d. O₂

17. Identify which pair has polar covalent bonds.

a. O₂ and Cl₂
b. H₂O and N₂
c. H₂O and H₂
d. H₂O and HCl

18. Which one of the following is the weakest force among the atoms?

a. Ionic force
b. Metallic force
c. Intermolecular force
d. Covalent force