Explore topic-wise InterviewSolutions in .

The correct choice is (a) True

Easiest explanation: Valence bond theory was initially introduced by London and Heitler and was developed by PAULING and others. It’s a CHEMICAL bonding theory that EXPLAINS the OVERLAPPING the atomic ORBITALS in order to form chemical bonds between atoms.

Right choice is (b) 180°

The best I can explain: A LINEAR molecule has a HYBRIDIZATION sp, in which the bonds between the central atom and other atoms are separated by 180°. For EXAMPLE, let’s TAKE carbon dioxide, it’s SHAPE is given by O=C=O.

The correct ANSWER is (B) Lattice energy

Explanation: When the ions are COMBINED to form an ionic compound that is a crystalline solid, a certain amount of energy is released and this is KNOWN as the lattice energy. Solubility, VOLATILITY, and hardness can be predicted from lattice energy.

Correct answer is (a) Lewis

For explanation I would say: The above statement says that the atoms achieve a stable octet configuration when joined with other atoms through chemical bonds as postulated by Lewis. An example of this is the formation of NaCl MOLECULE where Na and CL transfer ELECTRONS to each other forming Na^+ and Cl^–.

The CORRECT answer is (a) noble GASES

To ELABORATE: According to Kossel, Highly electropositive Alkali metals are separated from highly electronegative HALOGENS by noble gases. This is because Alkali metals are the 1^st group and halogens the 17^th group. Elements in 18^th group i.e. nobles are preceded by group 17 elements and succeeded by group 1 elements.

Right option is (B) True

To explain: Resonance STABILIZES the molecule as the resonance hybrid comprises of less energy than other CANONICAL STRUCTURES. Resonance is made of many structures that change frequently in molecules in order to maintain stability in the molecule.

The correct answer is (c) :C:

Explanation: An American CHEMIST G.N. Lewis CREATED Lewis symbols as a notation to REPRESENT the valance electrons in an atom. As the carbon atom has 4 electrons in its outer shell, it is represented by 4 dots AROUND it.

Right answer is (c) zero

The explanation: Zero OVERLAP means that the ORBITALS don’t overlap at all. When there is no overlapping the bond FORMATION doesn’t OCCUR. As we all know that the EXTENT of overlapping is dependent on the strength of the bond.

Correct option is (d) H2O

To elaborate: The DIPOLE movement is given by the PRODUCT of charge and the distance of separation between atoms. It is EXPRESSED in Debye units (D). For the molecules N2, CH4 and BeF2 the net dipole movement is zero as they CANCEL each other due to symmetry. But water molecule due to its V-shape exhibits dipole movement.

Correct CHOICE is (a) 3

To ELABORATE: The number of bonds that are created between two atoms in a molecule is the bond ORDER of that bond. The molecule carbon monoxide CO has a triple bond between the carbon and oxygen, so it’s bond order is 3.

Correct ANSWER is (c) Bent

The explanation is: The water molecule H-O-H has an arrangement of electrons in a tetrahedral. As it CONTAINS two bond pairs and lone pairs in the form of the molecule of TYPE AB3E2, it’s shape is bent i.e. neglecting the lone pairs.

The CORRECT option is (b) True

For explanation: Ionization energy is the MINIMUM amount of energy that is required to remove an electron from a neutral ISOLATED gaseous atom. The symbolic representation is given by A(g) → A(g)^+ + e^–. It is always negative as it requires energy that is ENDOTHERMIC in NATURE.

The correct choice is (d) H2O

The best explanation: The molecules LiCl, MGO, and SnCl4 are formed by IONIC BONDS as they transfer electrons from an electropositive atom, that DONATES to the electronegative atom, that accepts. Whereas H2O has covalent bonds as it shares electrons.

Correct ANSWER is (c) both exothermic and endothermic

Easiest explanation: Electron GAIN enthalpy is the enthalpy change for an atom in the ground state to gain an electron. In the CASE of an exothermic REACTION, the VALUE of electron gain enthalpy is negative, which means that it is releasing energy and vice-versa when it’s positive.

The CORRECT CHOICE is (d) NO2

The EXPLANATION is: Though octet rule is widely known, it does have a few limitations. The COMPOUND nitrogen dioxide NO2 doesn’t follow the octet rule. It’s a molecule with an odd number of electrons. Even the nitric oxide NO doesn’t follow.

Right answer is (b) 464.5 KJ mol^-1

The EXPLANATION is: We KNOW that H2O(G) → H(g) + OH(g); ΔH1 = 502 kJ mol^-1 and OH(g) → H(g) + O(g); ΔH2 = 427 kJ mol^-1. So the average bond ENTHALPY is given by their mean that is 427 + 502/2 = 464.5 KJ mol^-1. This method is used for polyatomic molecules like water.

The correct answer is (d) less

To explain I WOULD say: The rate of formation of an ionic bond MAINLY depends on the tendency to become CATION and anion from their original ground states. The tendency is maximum for metallic atoms WHOSE ionization energy is less than the other atoms.

The CORRECT answer is (d) HCl

For EXPLANATION: The molecule that is FORMED from the same ELEMENT is known as a homonuclear molecule and the molecule that is made up of 2 atoms is CALLED a diatomic molecule. But HCl is not a homonuclear diatomic molecule as it has different atoms.

Right OPTION is (B) side-wise overlapping

The best EXPLANATION: A pi-BOND is a TYPE of covalent bond in which the internuclear axes of the atoms are parallel to each other and for side-wise overlapping. The bond formed here is perpendicular to the internuclear axes.

Correct answer is (a) 788 KJ mol^-1

To ELABORATE: NaCl’s lattice enthalpy is given by 788 KJ mol^-1. To disassociate one mole of NaCl into one mole of Na^+ and one mole of Cl^-1 into an infinite distance, we need 788 KJ mol^-1 of ENERGY. When the ions are combined to FORM an ionic compound that is a crystalline SOLID, a certain AMOUNT of energy is released and this is known as the lattice energy.

Correct option is (d) in-phase overlap

To explain I WOULD say: A positive overlap results in BOND formation. When 2 p-orbitals are in phase, both the positive lobes overlap, THUS CREATING a positive overlap and result in the bond formation, thus it is called in-phase overlap.

The correct answer is (c) Octet rule

Best explanation: As per the electronic theory of chemical BOND that’s put forth by Lewis &KOSSEL states that the atoms follow the octet rule by sharing or transfer of electrons from ONE atom to the other to attain STABLE octet configuration.

The correct choice is (c) TRIAGONAL PYRAMIDAL

For explanation I would say: The molecule NH3 has a LONE pair and 3 bond pairs. As we know that the repulsion order is as follows: Lone pair-Lone pair is greater than Lone pair-Bond pair is greater than Bond pair-Bond pair. So the shape of molecule NH3 is TRIGONAL pyramidal, where the lone pair is away from the 3 bond pairs.

Right answer is (b) valence electrons

Easy explanation: As the postulate of Valence SHELL Electron PAIR Repulsion Theory (VSEPR), the shape of the molecule depends on the number of valence shell electron PAIRS AROUND the atom (both BONDED and non-bonded).

The correct option is (d) Young’s DOUBLE-slit method

For explanation: The equilibrium distance between the nuclei of two BONDED atoms in a molecule is known as bond length. It can be measured by spectroscopy, X-ray diffraction, and electron diffraction. Young’s double slit method is used for determining electromagnetic spectra.

Correct choice is (a) True

Explanation: Yes. electron gain enthalpy is the enthalpy CHANGE for an atom in the ground state to gain an electron. An atom gains an electron, thus FORMING negatively CHARGED ion also KNOWN as a cation. Symbolic representation is as follows: A(g) + e^– → A(g)^–.

The CORRECT option is (b) 1

Explanation: The group valance can be calculated from Lewis symbols either by subtracting it from eight (more than 4) or having it equal (less than 4). The halogen family has 7 ELECTRONS in their outer orbit. So 8 – 7 = 1. Therefore the valency of the halogen family is 1.

The correct option is (b) 1s^22s^22p^3

To explain I WOULD say: The electronic configuration of carbon in its GROUND state is GIVEN by 1s^22s^22p^4. When it’s in an excited state, that is when it loses an ELECTRON, that would be from 2p-orbital. So the excited state’s electronic configuration is 1s^22s^22p^3.

Right option is (a) Lone pair-Lone pair is greater than Lone pair-Bond pair is greater than Bond pair-Bond pair

Explanation: The repulsive interactions follow the above ORDER. The lone PAIRS are localized on the CENTRAL atom, each bonded pair is shared between TWO ATOMS. So, the lone pair electrons in a molecule occupy more space as compared to the bonding pairs of electrons.

Right ANSWER is (a) True

Easiest explanation: In the year 1919, Langmuir postulated the theory of covalent bond and its formation by combining with LEWIS theory. An example of this is the formation of Cl2, Two ATOMS of Cl combine by sharing the 7^th electron in its OUTER shell.

Correct ANSWER is (b) False

For EXPLANATION I would say: A sigma bond is always stronger than the pi bond. As we know that the bond STRENGTH is DECIDED by the extent of orbital’s OVERLAPPING. The extent of overlapping is more in sigma bond than in a pi-bond.

Correct choice is (a) 99pm, 198pm

Explanation: The half of the distance between TWO covalently bonded similar atoms in the same molecule is called covalent RADIUS, whereas the half of the distance between two similar atoms of DIFFERENT MOLECULES in a solid is KNOWN as van der Waal’s radius. Therefore covalent radius is smaller than the van der Waal’s radius.

Right ANSWER is (a) 104.5°

To explain: The water molecule is the V-shape, so the ANGLE between hydrogen through oxygen is GIVEN → by 104.5°. As we know the angle between TWO bonds from the same atom that is bonded to different atoms is called the bond angle.

Correct answer is (a) 1

To explain I would say: The formula for FINDING out the formula charge of an in a molecule = TOTAL number of valence ELECTRONS – total number of non-BONDING electrons – 1/2 (total number of bonding electrons). So here, a formal charge of central O is 6 – 2 – 6/2 = 1.