Quiz on Molecular Geometry and Hybridisation of Orbitals

What does VSEPR theory help predict?

• The color of molecules

• The geometry of molecules

• The temperature of molecules

• The mass of molecules

Answer explanation

VSEPR theory, or Valence Shell Electron Pair Repulsion theory, helps predict the geometry of molecules by considering the repulsion between electron pairs around a central atom, leading to specific molecular shapes.

Which molecular shape corresponds to four regions of high electron density?

• Octahedral

• Linear

• Tetrahedral

• Trigonal planar

Answer explanation

The tetrahedral shape corresponds to four regions of high electron density, where the electron pairs are arranged to minimize repulsion, resulting in a three-dimensional structure with bond angles of approximately 109.5 degrees.

What type of bond is formed by the head-to-head overlap of orbitals?

• Sigma (σ) bond

• Pi (π) bond

• Hydrogen bond

• Ionic bond

Answer explanation

A sigma (σ) bond is formed by the head-to-head overlap of atomic orbitals, allowing for a strong bond along the axis connecting the two nuclei. This distinguishes it from pi (π) bonds, which involve side-to-side overlap.

Which of the following is a characteristic of polar bonds?

• They occur when bonded atoms differ in electronegativities

• They have equal electronegativities

• They always form non-polar molecules

• They cannot exist in covalent compounds

Answer explanation

Polar bonds occur when there is a difference in electronegativities between the bonded atoms, leading to an unequal sharing of electrons. This characteristic distinguishes them from non-polar bonds, which have equal electronegativities.

What is the molecular geometry of ammonia (NH3)?

• Linear

• Trigonal pyramidal

• Trigonal planar

• Tetrahedral

Answer explanation

Ammonia (NH3) has a trigonal pyramidal molecular geometry due to the presence of one lone pair of electrons on the nitrogen atom, which pushes the hydrogen atoms down, creating a pyramid shape.

Which hybridisation corresponds to a central atom with five bonding pairs?

• sp3

• sp

• sp3d

• sp2

Answer explanation

The hybridisation corresponding to a central atom with five bonding pairs is sp3d. This involves one s orbital, three p orbitals, and one d orbital, allowing for five hybrid orbitals to accommodate the bonding pairs.

What is the electronic geometry of a molecule with four bonding pairs and no lone pairs?

• Octahedral

• Tetrahedral

• Linear

• Trigonal planar

Answer explanation

The electronic geometry of a molecule with four bonding pairs and no lone pairs is tetrahedral. This arrangement minimizes repulsion between the bonding pairs, resulting in a three-dimensional shape with bond angles of approximately 109.5°.

In which molecular shape do lone pairs exert the strongest repulsion?

• Lone pair to lone pair

• No repulsion occurs

• Lone pair to bonding pair

• Bonding pair to bonding pair

Answer explanation

Lone pairs exert the strongest repulsion due to their concentrated negative charge. This leads to greater repulsion between lone pairs compared to bonding pairs, making 'lone pair to lone pair' the correct choice.

What is the molecular geometry of carbon dioxide (CO2)?

• Tetrahedral

• Trigonal planar

• Octahedral

• Linear

Answer explanation

Carbon dioxide (CO2) has a linear molecular geometry due to its two double bonds with oxygen atoms and no lone pairs on the central carbon atom, resulting in a straight-line arrangement.

Which hybridisation involves one s-orbital and two p-orbitals?

• sp2

• sp

• sp3

• sp3d

Answer explanation

The sp2 hybridisation involves one s-orbital and two p-orbitals, resulting in three equivalent sp2 hybrid orbitals. This is commonly seen in molecules like ethylene (C2H4), where the carbon atoms are sp2 hybridised.