Question 1

A molecule with the formula AX₄ uses __________ to form its bonds.

Accepted Answer

The formula indicates that there are two central atoms, A and B, with 1 and 14 bonded atoms respectively. The S1U1 and S1 in the formula represent lone pairs of electrons on A and B, respectively. The P13 and P12 indicate the number of valence electrons on A and B, respectively. To form the bonds in this molecule, A and B would hybridize their valence orbitals, which in this case would be s, p, and d orbitals. However, based on the formula, there are not enough electrons to form d orbitals on A or B, so we can eliminate answer D and E. The remaining choices involve sp hybrid orbitals, which would not allow for the necessary number of bonds to be formed, so we can eliminate answer A. The correct answer is therefore C, which involves sp ³ hybrid orbitals.

Question 2

In molecular orbital theory, combination of two 2p atomic orbitals may give rise to either σ orπ type molecular orbitals.

Accepted Answer

When two 2p atomic orbitals combine, they can do so in a manner that aligns them end-to-end or side-by-side. The end-to-end overlap produces a sigma (σ) molecular orbital, characterized by its cylindrical symmetry around the bond axis, while the side-by-side overlap results in a pi (π) molecular orbital, which has a nodal plane where the electron density is zero, perpendicular to the bond axis.

Question 3

According to valence bond theory, overlap of bonding orbitals of atoms will weaken a bond, due to electron-electron repulsion.

Accepted Answer

According to valence bond theory, the overlap of bonding orbitals of atoms strengthens a bond because it allows electrons from each atom to be shared between the atoms, leading to a lower energy state and a stronger bond due to the attraction between the positively charged nuclei and the shared electrons.

Question 4

In the valence bond treatment, a π bond is formed when two 2p orbitals overlap side to side.

Accepted Answer

This is correct according to the valence bond theory, where a π bond is formed when two atomic orbitals, often p orbitals, overlap side by side.

Question 5

Overlap of two sp² hybrid orbitals produces a π bond.

Accepted Answer

Overlap of two sp^3 hybrid orbitals produces a sigma (σ) bond, not a π bond. π bonds are formed by the side-to-side overlap of p orbitals.

Question 6

In applying molecular orbital theory, the bond order is calculated in the same way as with Lewis structures.

Accepted Answer

In molecular orbital theory, bond order is calculated by subtracting the number of anti-bonding electrons from the number of bonding electrons and dividing by two. This method is different from the one used in Lewis structures, which calculates bond order by counting the number of electron pairs shared between two atoms.

Question 7

In molecular orbital theory, molecules with an even number of electrons will have bond orders which are whole numbers.

Accepted Answer

According to the molecular orbital theory, the bond order is the difference between the number of bonding electrons and the number of antibonding electrons, divided by two. Since only whole numbers of electrons can exist in atomic orbitals, the bond order of molecules with an even number of electrons will always be a whole number.

Question 8

According to valence bond theory, which orbitals on N and H overlap in the NH₃ molecule?

Accepted Answer

In NH₃, nitrogen undergoes sp³ hybridization, and these sp³ orbitals overlap with the 1s orbitals of hydrogen atoms to form N-H bonds.

Question 9

A molecule with the formula AX₃ uses __________ to form its bonds.

Accepted Answer

A molecule with the formula AX₃ typically forms a trigonal planar shape, which involves sp² hybridization.

Question 10

Valence bond theory is able to explain why molecular oxygen is paramagnetic.

Accepted Answer

Valence bond theory cannot explain the paramagnetic nature of molecular oxygen; molecular orbital theory is needed to account for the unpaired electrons in oxygen.

Question 11

Hybrid orbitals of the sp³d type occur in sets of four.

Accepted Answer

Hybrid orbitals of the type described (sp^3d) occur in sets of five, not four, as they involve the mixing of one s orbital, three p orbitals, and one d orbital.

Question 12

A molecule with the formula AX₂ uses __________ to form its bonds.

Accepted Answer

The correct answer is A because AX2 molecules use sp hybrid orbitals to form their bonds. This is because the central atom A has two valence electrons, and each of the two X atoms has one valence electron. The sp hybrid orbitals are formed by the mixing of one s orbital and one p orbital on the central atom A. This results in two sp hybrid orbitals that are oriented in a linear fashion. The two X atoms then overlap with the sp hybrid orbitals on the central atom A to form two sigma bonds.

Question 13

A carbon-carbon double bond in a molecule may give rise to the existence of cis and trans isomers.

Accepted Answer

The carbon-carbon double bond restricts rotation around the bond, allowing for the possibility of different spatial arrangements of the substituents. If the two substituents are on the same side of the double bond, it is called the cis isomer. If they are on opposite sides, it is called the trans isomer.

Question 14

In molecular orbital theory, combination of two atomic orbitals produces two molecular orbitals.

Accepted Answer

When two atomic orbitals combine, they form two molecular orbitals: a bonding molecular orbital and an antibonding molecular orbital.

Question 15

Valence bond theory explains the bonding in diatomic molecules such as HCl without resorting to the use of hybrid orbitals.

Accepted Answer

Valence bond theory can explain bonding in diatomic molecules using the overlap of atomic orbitals without needing hybridization. Hybridization is typically used to explain bonding in larger molecules where the atomic orbitals may not have the correct symmetry to form bonds.

Question 16

According to molecular orbital theory, all diatomic molecules with an even number of electrons will be diamagnetic.

Accepted Answer

Molecular orbital theory suggests that whether a diatomic molecule is diamagnetic or paramagnetic depends on the electron configuration in its molecular orbitals. If all electrons are paired, the molecule is diamagnetic; if there are unpaired electrons, it is paramagnetic. This is not solely determined by having an even number of electrons.

Question 17

Atoms of period 3 and beyond can undergo sp³d² hybridization, but atoms of period 2 cannot.

Accepted Answer

This statement is true. Atoms of period 2 have only one filled energy level (n=2), whereas atoms of period 3 and beyond have at least one additional filled energy level (n=3, 4, etc.), allowing for hybridization to occur. The hybridization mentioned in the statement is a common hybridization scheme for atoms in period 3 and beyond.

Question 18

The angles between sp² hybrid orbitals are 109.5°.

Accepted Answer

The angles between sp^3 hybrid orbitals are 109.5°, not sp hybrid orbitals.

Question 19

In the valence bond treatment, overlap of an s orbital on one atom with an sp³ orbital on another atom can give rise to a σ bond.

Accepted Answer

This is a correct statement in the valence bond theory. Overlap of an s orbital on one atom with an sp, sp2, or sp3 hybrid orbital on another atom can also give rise to σ bonds.

Question 20

A carbon-carbon triple bond in a molecule may give rise to the existence of cis and trans isomers.

Accepted Answer

Cis and trans isomers require restricted rotation around a bond, which is characteristic of double bonds, not triple bonds. Triple bonds are linear and do not allow for cis or trans configurations due to their geometry.

Quiz 11: Theories of Covalent Bonding

A molecule with the formula AX4 uses __________ to form its bonds.