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Atoms which contain 8 electrons in the outermost shell are stable and less reactive.

A chemical bond is an attractive force between two atoms in a molecule.

Here, B atom in BF₃ is sp² hybridized and one of its p orbital is empty. N in NH₃ is sp³ hybridized and are of its hybrid orbitals is occupied by a lone-pair of electrons. During the reaction a co-ordinate bond is formed due to one-side sharing of electron pair.

BF₃ + NH₃ → [F₃B ←: NH₃] → F₃B ← NH₃

There is no change in the hybridization of any of the two atoms in this reaction

In first figure, the ++ overlap is equal to +- overlap and therefore, these cancel out and net overlap is zero.
In second figure, no overlap is possible because the two orbitals are perpendicular to each other.

Correct Option is : (A)\(BF_3\)

\(BF_3\) is a electro deficient species . Because B atom contain only six in their outer shell in \(BF_3\) molecule . It does not follow octet rule.

Option : (A) BF₃

Dimethyl ether will have larger bond angle. There will be more repulsion between bond pairs of CH₃ groups attached in ether than between bond pairs of hydrogen atoms attached to oxygen in water. The carbon of CH₃ in ether is attached to three hydrogen atoms through σ bonds and electron pairs of these bonds add to the electronic charge density on carbon atom. Hence, repulsion between two —CH₃ groups will be more than that between two hydrogen atoms.

A sigma bond is formed by axial overlapping of atomic orbital. It is always formed between two half filled atomic orbitals along their internuclear axis i.e the line joining the centers of the nuclei of two atoms. 2p_y, and 2p_y will not form sigma bond because they can only undergo sidewise overlapping of atomic orbitals and form pi bond.

The answer is (c) SiF₅

Dipole moment is directly proportional to electronegativity. Electronegativity decreases with increasing atomic size. Thus, the ion having smallest size has maximum electronegativity and thus, maximum dipole moment. Also, atomic size increases down the group. Therefore, in the above ions, Li⁺ has smallest size. Hence, it has maximum dipole moment.

As we move down the group in periodic table, the bond’s covalent character increases, which invariably is related to the decrease in difference between the electronegativities of the bonding atoms, which means decrease in polarity of the molecule. Also as the size of anion increases, the tendency to polarise cation increases. Covalent compounds are insoluble in water. AgF will be most ionic compound. Therefore, the order of solubility of halides of silver will be:
Agl < AgBr < AgCl < AgF

N² > O² > Cl² > F² .

Both NH₃ and NF₃ are pyramidal in shape with one lone pair on N. However, as F has higher electronegativity than H, the electron pair is attracted more towards F in NF₃, i.e., the bond pairs of electrons are away from N or in other words, distance between bond pairs is more. Hence the repulsions between bond pairs in NF₃ is less than in NH₃. Thus the lone pair repels the bond pairs of NF₃ more than it does in NH₃. As a result, the bond angles decreases to 102.4º  only.

Hybridization of carbon atom in CCl₄ is sp³.
Hybridization of oxygen atom in H₂O is sp³.
Hybridization of carbon atom in CO₂ is sp.
Hybridization of sulphur atom in SO₂ is sp².

This is because both N and F are small and hence have high electron density. So they repel the bond pairs thereby making the N-F bond length larger.

(a)  The hybrid orbitals are equivalent in energy and shape. 

(b)  The orbitals taking part in hybridization must have only  a small difference in energy. 

(c)  The number of hybrid orbitals is the same as the number of atomic orbitals that undergo hybridization. 

(d)  Both half filled and completely filled orbitals take part in hybridization. 

(e)  Hybrid orbitals form more stable bonds. 

(f)  The type of hybridization gives the shape of molecules.

• The electrons in an atom are found in atomic orbitals, the electrons in a molecule are found in molecular orbitals. 

• The molecular orbitals are formed by the combination of atomic orbitals of comparable energies and proper symmetry. 

• The BMO has lower energy and hence greater stability than the corresponding ABMO. 

• The molecular orbitals are filled by electrons in accordance with Aufbau principle, Pauli’s exclusion principle, and the Hund’s rule.

1. When two atomic orbitals having same energy and proper symmetry are approaching each other molecular orbitals are formed by the linear combination of atomic orbitals.

2. The no. of molecular orbitals formed is equal to no. of atomic orbitals undergoing combination.

3. During LCAO , two types of molecular orbitals are formed, bonding and antibonding molecular orbitals.

4. Electrons are added to various molecular orbitals according to Aufbau‟s principle, Paul‟s exclusion principle and Hund‟s rule.

KK(σ2s)² (σ*2s)² σ2pz ² (π2px² = π2py²)(π *2px‟= π*2py‟)

Bond order= ½[N_b-N_a]

= ½[10-6]

= 2 

a. Forces of attraction : 

The nucleus of one atom attracts the electrons of the other atom and vice-versa.

b. Forces of repulsion :

The electron of one atom repels the electron of the other atom and vice-versa (as electrons are negatively charged). 

There is repulsion between the two nuclei (as the nuclei are positively charged).

Formation of a covalent bond is favoured by 

1. High ionisation enthalpy of the combining elements. 

2. Nearly equal electron gain enthalpy and equal electro negativities of combining elements. 

3. High nuclear charge and small atomic size of the combining elements. 

In a covalent bond if the pair of electrons are shared unequally (asymmetrically) between the atoms are called polar covalent bond.

In a covalent bond if the pair of electrons shared equally (symmetrically) between the atoms called non-polar covalent bond.

A covalent bond is formed by the overlap of half-filled atomic orbitals.

Sigma (σ) Bond

1. σ – bond is formed by the axial overlap of the atomic orbitals.

2. The bond is quite strong. 

3. Only one lobe of the p-orbitals is involved in the overlap. 

4. Electron cloud of the molecular orbital is symmetrical around the inter-nuclear axis.

Pi (π) Bond

1. π – bond is formed by the sidewise overlap of atomic orbitals

2. It is comparatively a weaker bond.

3. Both lobes of the p-orbitals are involved in the overlap.

4. The electron cloud is not symmetrical.

The correct option is- (d) O₂²⁺

1. The combining atomic orbitals should have comparable energies. For example, is orbital of one atom can combine with 1s atomic orbital of another atom, 2s orbital can combine with 2s orbital and so on.

2. The combining atomic orbitals must have proper orientations so that they are able to overlap to a considerable extent.

3. The extent of overlapping should be large.

The following conditions are required for the linear combination of atomic orbitals (LCAO) to form molecular orbitals :

i. The combining atomic orbitals must have comparable energies.

So, Is orbitals of one atom can combine with 1 s orbital of another atom but not with 2s orbital, because energy of 2s orbital is much higher than that of 1 s orbital.

ii. The combining atomic orbitals must have the same symmetry along the molecular axis.

Conventionally, 

z axis is taken as the internuclear axis. 

So even if atomic orbitals have same energy but their symmetry is not same they cannot combine. 

For example, 

2s orbital of an atom can combine only with 2p_z orbital of another atom, and not with 2p_x or 2p_y orbital of that atom because the symmetries are not same. p is symmetrical along z axis while px is symmetrical along x axis.

iii. The combining atomic orbitals must overlap to the maximum extent. 

Greater the overlap, greater is the electron density between the nuclei and so stronger is the bond formed.

Sulphur dioxide

O = S → O

Ammonium (NH₄⁺)

H₃N → N⁺

The correct answer is:- (c) [Fe(CN)_6]^4-

The correct option is- (a) NH₄Cl

1. Orbitals on a single atom only would undergo hybridization. 

2. The orbitals involved in hybridisation should not differ largely in their energies. 

3. The number of hybrid orbitals formed is equal to the number of hybridising orbitals. 

4. The hybrid orbitals form stronger directional bonds than the pure s, p, d atomic orbitals. 

5. It is the orbitals that undergo hybridisation and not the electrons.

6. Concept of hybridisation is useful in explaining the shape of molecules.

Correct option is D) 4

C) intermixing

1. Hydrogen bond is formed between molecules in which hydrogen atom is attached to an atom of an element with large electronegativity and very small size (F, O, N). Because in hydrogen bond the molecules associate themselves and hence possess higher B.P’s and M.P’s. 

2. The hydrogen bond formed between two molecules is called inter-molecular hydrogen bond. 

3. The hydrogen bond formed between different groups of the same molecule is called intramolecular hydrogen bond.

In the formation of molecules, the atomic orbitals of the atoms may hybridise. 

1. It is the process of mixing up of atomic orbitals of an atom to form identical hybrid orbitals. 

2. This takes place only during the formation of bond. 

3. There should not be much difference in the energies of the orbitals that hybridise. 

4. The number of hybrid orbitals formed is equal to the number of hybridising atomic orbitals. 

5. Hybrid orbitals form a bonds only not n bonds.

Correct Option is : (D) HCl is higher than that of HBr

The electronegativity of chlorine is greater than Bromine due to this chlorine withdraw bonding electron more strongly than Bromine . Therefore, HCl has higher dipole moment than HBr.

Option : (D) HCl is higher than that of HBr

B) Chemical bond

Electropositive character: The ability to lose electrons and become a positively charged ion of an atom is called the electropositive character.

Covalent compounds: The compounds formed by the covalent bonds are covalent compounds.

A dipolar molecule attracting announcer dipolar molecule is called dipole-dipole attraction.

Ionic bond: The electrostatic attraction force that keeps cation and anion together to form a new electrically neutral compound is called ‘Ionic bond’.

Polar bonds: These are formed due to unequal sharing of electrons by the combining atoms.

Vander Waal’s forces are purely electrostatic forces operating between molecules at a short distance.

Ionic compounds: The compounds formed by the ionic bonds are called compounds.

Polar solvent: Polar solvents are the compounds such as water and liquid ammonia which have dipole moments and consequently high dielectric constants. The solvents are capable of dissolving ionic compounds or covalent compounds that ionize.

Molecules having two oppositely charged poles are called polar molecules.

Formation of molecules: Atoms combine and form molecules. This is called the formation of molecules

Non-polar solvent: Non-polar solvents are compounds such ethane and benzene, which do not have dipole moments. These do not dissolve in but will dissolve nonpolar covalent compounds