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Chapter:

11. Which of Bohr’s postulates was incorrect?

Energy of electrons is quantized Momentum of electrons is quantized Electrons release energy when shifting from excited state to ground state Electrons revolve around the nucleus in fixed circular orbits

Electrons revolve around the nucleus in fixed circular orbits

Heisenberg uncertainty principle implies that exact position and momentum of electrons cannot be known with certainty and hence, definite circular paths are not feasible. Certain regions around nucleus (called orbitals) have a high probability of existence of electrons.

Hint Answer

12. 4f orbital has higher energy than 5p.

True False

True

Sum of principal and azimuthal quantum numbers for 4f is (4+3=) 7 and that for 5p is (5+1=) 6. As a general rule, higher sum, higher is energy.

Hint Answer

13. Which of following orbitals do not exist?

3p 4s 2s 3f

3f

For principal quantum number 3, only possible values of azimuthal quantum number are 0, 1, and 2. Azimuthal quantum number of an f-orbital is 3.

Hint Answer

14. VSEPR stands for Valence Shell Electron Pair Repulsion. This ory helps us predict:

Bond angles Bond length Electron energy Shell radius

Bond angles

VSEPR ory implies that electrons in valence shell arrange mselves in a manner so as to experience minimum repulsion from or electrons. For e.g., in a CH₄ molecule, all bonds are symmetrically arranged at approximately 109°.

Hint Answer

15. In water, bond angle between H-O H-O bond is less than 109° Why?

The H atoms attract each other Oxygen atom is much larger than Hydrogen atoms Lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion VSEPR theory does not apply for planar molecules like water

Lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion

Bond angle is 109° for symmetric molecules like methane. However, it is known that repulsion between a lone pair and a bond pair is more than that between two bond pairs. Hence, bond angle is reduced from 109° so as to experience minimum repulsion from lone pairs.

Hint Answer

16. For covalent molecules, van der Waals radius is always greater than a covalent radius.

True False

True

Van der Waals radius is half internuclear distance between two non-bonded atoms on ir closest approach whereas covalent radius is half bond length of a homo-nuclear molecule. Since distance between two bonded atoms is less than non-bonded atoms, hence answer.

Hint Answer

17. If E1 is bond enthalpy of a sigma-bond and E2 is that of a pi-bond, n:

E1 > E2 E1 = E2 E1 < E2 Can’t be predicted

E1 > E2

Since overlap of orbitals in a sigma-bond is along internuclear axis contrary to sideways overlap in pi-bonds, bonding is more effective in a sigma-bond. Hence, E1 > E2. Though, total energy of a double bond is more than a single bond)

Hint Answer

18. With an increase in bond length, bond energy:

increases decreases may either increase or decrease does not change

decreases

The coulombic force of attraction is inversely proportional to square of a distance between charges. As internuclear distance in a bond increases, force of attraction between nuclei and electrons decreases.

Hint Answer

19. sp³ hybridization is present in which of following molecules?

BeCl₂ H₂O C₂H₄ BCl₃

H₂O

Hybridization takes place between one 2s and three 2p orbitals of Oxygen so as to minimize electronic repulsion. BeCl₂, C₂H₄, and BCl₃ have sp, sp², and sp² hybridization respectively.

Hint Answer

20. As we move down a group, electronegativity of elements generally:

Increases Decreases Increases and then decreases Decreases and then increases

Decreases

As we move down a group, atomic size increases which means that valence electrons are much farr from nucleus and hence experience less force of attraction. Hence electronegativity decreases down group.

Hint Answer

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All Chapters

View all Chapter and number of question available From each chapter from Material-Science

Atomic Structure and Interatomic Bonding

Atomic Structure and Interatomic Bonding

Structure of Crystalline Solids

Structure of Crystalline Solids

Imperfections in Solids

Imperfections in Solids

Diffusion

Mechanical Properties of Metals

Mechanical Properties of Metals

Dislocations and Strengthening Mechanisms

Dislocations and Strengthening Mechanisms

Failure

Phase Diagrams

Phase Transformations in Metals

Phase Transformations in Metals

Applications and Processing of Metal Alloys

Applications and Processing of Metal Alloys

Structures and Properties of Ceramics

Structures and Properties of Ceramics

Topics

This Chapter consists of the following topics

Atomic Structure and Interatomic Bonding

Which of Bohr’s postulates was incorrect?

4f orbital has higher energy than 5p.

Which of following orbitals do not exist?

VSEPR stands for Valence Shell Electron Pair Repulsion. This ory helps us predict:

In water, bond angle between H-O H-O bond is less than 109° Why?

For covalent molecules, van der Waals radius is always greater than a covalent radius.

If E1 is bond enthalpy of a sigma-bond and E2 is that of a pi-bond, n:

With an increase in bond length, bond energy:

sp³ hybridization is present in which of following molecules?

As we move down a group, electronegativity of elements generally:

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