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D) All of these

 Correct option is A) Kossel 

Valence electrons :

1. Number of electrons in the outermost orbit or an atom is called its valence electrons. 

2. Ex: Na (Z = 11). It has 2e^– in I orbit, 8e^– in II orbit and 1e^– in III orbit. 

3. So number of valence electrons in Na atom are ‘l’.

Covalency of an element: 

1. Number of valance electrons which are taking part in covalent bond is called covalency. 

2. The electron configuration of Boran is 1s² 2s² 2p¹. 

3. It has three valance electrons. 

4. So its covalency is 3.

(i) True 

(ii) True

The number of electrons which an atom contributes towards mutual sharing during the formation of a chemical bond called its covalency in that compound.

The maximum covalency of chlorine is +7.

Ionic compounds does not ionize in ether i.e. ether cannot separate the cations and anions of ionic solids.

(i) A and R both are correct, and R is the correct explanation of A.

NaCl is an ionic compound and gives Cl^- which results with Ag⁺ to form AgCl , whereas CCl₄ is covalent compound, therefore it does not give ions in aqueous solution.

Sodium metal has weak metallic bond whereas sodium chloride (NaCI) contains strong ionic bond between Na⁺ and CI⁻, So, NaCI is harder than sodium metal.

(i) Since, ionic compounds are polar in nature, so, these compounds are soluble in water but covalent compounds are generally non-polar, so these are insoluble in water. 

(ii) Since, ionic compounds possess strong electrostatic forces of attraction, so melting points of ionic compounds are higher than covalent compounds.

Solid sodium chloride has crystalline structure in which the ions are not free to move. The ions became mobile when it is in molten state and thus, the electricity can be conducted.

Properties of ionic compounds

(a) Non-directional nature of ionic bond : These compounds do not exist as individual molecules. Instead they are often hard solids, always made up of ions held together by strong electrostatic forces of attraction between ions with opposite charge.

(b) Electrical conductivity : When put into water, the ions fall apart. The solution can thus conduct electricity. Similarly, these compounds conduct electricity in the fused state also.

(c) Melting and boiling points : These compounds generally have high melting points. This is because a lot of thermal energy is required to break down the inter-ionic forces and form a liquid. Similarly, they possess high boiling points.

(d) Solubility : These compounds are usually soluble in water but insoluble in benzene or other organic solvents.

In it the ions occupy certain fixed lattice positions in the crystals and do not move. Hence they do not conduct.

Ammonia has dipole moment due to pyramidal structure but is BF₃ the dipole moment is zero due to symmetrical planar structure.

The dipole moment of BF₃ is zero.

Because BF₃ has symmetrical shape, the net dipole moment is zero and thus it is non – polar.

(C) is least contributing towards resonance hybrid because negative charge is at less electronegative Carbon, positive charge is on Oxygen is more electronegative.

1. The bond between two elements in group 17(VILA) of the periodic table is likely to be ionic.

2. In the reaction of Cl₂ + 2K1→ 2KCl +I₂ the conversion of 21 to I₂ is deemed as oxidation.

3. The covalent molecule containing three single covalent bonds is ammonia.

4.  The molecule of water combines with a proton to form a hydronium ion.

5.  For formation of an electrovalent bond between elements ‘X’ and ‘ Y’ which are a metal and non-metal respectively, X should have a low ionization potential and ‘Y’ a high electron affinity

Dipole moment = q x r

μ = 0.50D = 0.50 × 10⁻¹⁸ stat C cm

r = 1.41 x 10^-8 cm

q = \(\frac{\mu}{r}\) = \(\frac{0.50\times10^{-18}\,stat \,C\,cm}{1.41\times10^{-8}cm}\)

Now, Fraction of charge = \(\frac{Charge\,present}{Electronic\,charge}\)

= \(\frac{0.35\times10^{-10}}{4.8\times10^{-10}}\) = 00.7

\(\therefore\) \(\delta_A\) = +0.07

and \(\delta_B\) = -0.07

Since the atomic radius increases and electronegativity decreases from HF to HI, therefore dipole moment of hydrogen halides decreases from HF to HI.

The H₂O molecules has a dipole moment of 1.84 D. There are two OH bonds in H₂O molecule. The O-H bonds are polar and has dipole moment of 1.5 D. Since the water molecule has a net dipole, hence the two O-H dipoles are not in a straight line opposing each other. This rule out the linear structure (H-O-H) for water. The two O-H bonds cannot lie along the same line in the direction also. Therefore, the two O-H bonds in H₂O molecule must be inclined to each other at certain angle. Thus H₂O molecule has an angular shape.

The CO₂ molecules has zero dipole moment. In CO₂, there are two C=O bonds. Each C=O bond is a polar bond. This means each bond has a dipole moment. Since, the net dipole of the CO₂ molecule is zero, hence the two bond dipoles, and hence the two bonds must be just opposite to each other, i.e., the two bonds must be at 180° relative to each other. Thus CO₂ is a linear molecule.

Hybridisation is defined as the mixing of the atomic orbitals belonging to the same atom but having slightly different energies so that a redistribution of energy takes place between them resulting in the formation of new orbitals of equal energies and identical shapes. The new orbitals thus formed are known as hybrid orbitals

Hybridisation of P in PCI₅ : sp³d

Hybridisation of C in CCI₄ ∶ sp³

Hybridisation of Ni in [Ni(CO)₄] : sp³

Hybridisation of B in BF₃ ∶ sp³d

Hybridisation is defined as the process of intermixing of the orbitals of slightly different energies so as to redistribute their energies, resulting in the formation of new set of orbitals of equivalent energies and shape.

(a)(i) B

(ii) A

(b) (i) Reduction

(ii) Oxidation

(iii) Reduction

Potassium chloride conducts electricity in water because the forces of attraction between positive and negative charged ions become weak in water and hence the ions become mobile. On the other hand, the HCl bond is a polar covalent compound, which means that there is a partial positive charge on H and a partial negative charge on Cl.. Hence it also ionizes in water and forms ions and conducts electricity.

During the formation of a non-polar covalent bond between two similar atoms or dissimilar atoms, the atoms involved in sharing share the electrons equally. The molecule of methane has four carbon-hydrogen single covalent bonds. It is a non-polar covalent compound as the electrons are shared by the carbon and hydrogen atoms equally and hence the shared pair lies between the atoms at an equal distance from both carbon and

Non-polar covalent compound(Methane,CH₄)

1. Covalent compounds are said to be non-polar when shared pair of electrons are equally distributed between the two atoms.

2. No charge separation takes place.The covalent molecule is symmetrical and electrically neutral.

Polar covalent compound (HCl)

1. Covalent compounds are said to be polar when shared pair of electrons are unequally distributed between the two atoms.

2. Charge separation takes place.The atom which attracts electrons more strongly develops a slight negative charge while the other develops a slight positive charge. 

Fluoride ion is negatively charged while neon atom is neutral.

(b) sharing of electrons

(c) Fluorine

(b) electron acceptors

Bond length : 

It is the inner-nucleus distance between the two atoms in a molecule. It is measured in Angstrom, 1 Å = 10^-8 cm.

Octet rule decides whether given element is stable or not. 

Octet rule : 

1. 'The atoms of elements tend to undergo chemical changes that help to leave their atoms with eight outer shell electrons.” 

2. It was found that the elements which participate in chemical reaction get octet (or) ns² np⁶ configuration similar to that of noble gas elements.

Role of octet in chemical properties of elements : 

1. Except He remaining inert gas elements have 8 electrons in their outermost orbit. Since these elements are having stable octet configuration in their outermost orbit, they are very stable. 

2. They do not allow the outermost electrons to take part in chemical reactions. 

3. So by having octet configuration for these elements we can conclude these are chemically inertial. 

4. If any group of elements (take halogens) which contain 7 electrons in their outermost orbit, they require only 1 e^- to get octet configuration. 

5. So they try to participate in chemical reaction to get that 1 difference electron for octet configuration.

6. Similarly, Na contains 2, 8, 1 as its electronic configuration. 

7. So it loses le^- from its outermost shell; it should have 8e^- in its outer shell and get the octet configuration. 

8. Thus the octet rule helps in explaining the chemical properties of elements.

Electronic theory of valence :

• Electronic theory of valence was proposed by Kossel and Lewis in 1916.
• They gave a logical explanation of valence which was based on the inertness of noble gases (that is, octet rule developed by Lewis).
• According to Lewis, the atom can be pictured in terms of a positively charged ‘kernel’ (the nucleus plus inner electrons) and outer shell that can accommodate a maximum of eight electrons. This octet of electrons represents a stable electronic arrangement.
• Thus, according to this theory, during the formation of a chemical bond, each atom loses, gains or shares outer electrons so that it achieves stable octet.
• The formation of NaCl involves transfer of one electron from sodium (Na) to chlorine (Cl). Na⁺ and Cl^- ions are formed which are held together by chemical bond. The formation of H₂, F₂, Cl₂, HCl, etc., involves sharing of a pair of electrons between the atoms. In both the cases, each atom attains a stable outer octet of electrons.

(c) noble gases

Octet rule : 

Presence of 8 electrons in the outermost shell of an atom or a molecule is called ‘octet rule’.

D) All of these

bond angle

The shape of the molecule is determined approximately by bond angle.

1) When covalent bond formed between any two atoms, irrespective of the nature of the atoms, the bond lengths and bond energies’ are expected to be same. But practically it was observed that bond lengths and bond energies are not same when the atoms that form the bond are different.

2) This theory fails to explain the shapes of molecules.

D) Noble gases

 Correct option is  D) 4

 Correct option is  D) All of these

B) Lewis, electron

Formal charges on atoms labelled as 1, 2, 3 are calculated as shown below :

Structure (I) :

 Structure (II) :

Structure (III) : 

While determining the best Lewis structure per molecule, the structure is chosen such that the formal charge is as close to zero as possible. The structure having the lowest formal charge has the lowest energy.

In structure (I), the formal charge on each atom is 0 while in structures (II) and (III) formal charge on carbon is 0 while oxygens have formal charge -1 or +1. 

Hence,

The possible structure with the lowest energy will be structure (I). 

Thus,

Formal charges help in the selection of the lowest energy structure from a number of possible Lewis structures for a given species.

B) Linus Pauling

C≡N > C=N > C-N

Note : 

Average bond lengths for some single, double and triple bonds :

Option : a. covalent > hydrogen > vander waals

A) Sidgwick and Powell