Question

A triatomic molecule must be either linear with a bond angle of \(180^{\circ}\) or else (1) Pyramidal (2) Tetrahedral (3) Bent (4) L-shaped

Short answer

Bent

Step-by-step solution

Identify the Type of Triatomic Molecule

A triatomic molecule consists of three atoms. This molecule can either be linear or adopt one of several non-linear shapes.

Determine Linear Shape

A linear shape for a triatomic molecule has a bond angle of \(180^{\circ}\). If the given triatomic molecule has this bond angle, it is classified as linear.

Evaluate Other Shapes

If the molecule is not linear (i.e., does not have a bond angle of \(180^{\circ}\)), consider the other possible shapes: Pyramidal, Tetrahedral, Bent, or L-shaped.

Match Given Shapes

Among the given options, identify which shape a triatomic molecule can actually adopt. Triatomic molecules cannot form Pyramidal or Tetrahedral structures because such shapes require more than three atoms.

Confirm Suitable Shape

A triatomic molecule in a non-linear form would be Bent due to the presence of a lone pair(s) on the central atom, causing a bond angle different from \(180^{\circ}\). Hence, the correct answer is Bent.

Key concepts

molecular geometry

Molecular geometry is the 3D arrangement of atoms within a molecule. Determining this structure helps in understanding the molecule’s properties and behavior. By knowing the molecular geometry, we can predict:

• Chemical reactivity
• Physical properties (boiling/melting points)
• Polarity

In triatomic molecules, molecular geometry can be either linear or non-linear.
If the atoms form a straight line, the geometry is linear.
Non-linear geometries arise due to lone pairs causing bonds to bend.

bond angles

Bond angles are the angles formed between two bonds that originate from the same atom. They are crucial for determining molecular shape. For a triatomic molecule:

• If the bond angle is exactly \(180^{\circ}\), the molecule is linear.
• If the bond angle is less than \(180^{\circ}\), the molecule is non-linear.

Bent shapes have bond angles typically around \(104.5^{\circ}\), as seen in water (H2O).

non-linear molecules

Non-linear molecules occur when the atoms do not form a straight line. This happens due to:

• Lone pairs on the central atom
• Electrostatic repulsion between electron pairs

In triatomic molecules, non-linear shapes are often described as bent. Examples include:

• Water (H2O)
• Sulfur dioxide (SO2)

The presence of lone pairs causes these molecules to have bond angles less than \(180^{\circ}\).

lone pairs

Lone pairs are valence electron pairs that are not used in bonding. They greatly affect molecular shape:

• By repelling bonding pairs
• Creating larger bond angles between bonding pairs than expected

In triatomic molecules:

• A lone pair on the central atom causes a bent shape.
• This leads to bond angles less than \(180^{\circ}\).

For example, in water (H2O), the oxygen atom’s lone pairs push the hydrogen atoms closer, resulting in a bond angle of about \(104.5^{\circ}\).

linear molecules

Linear molecules have a bond angle of \(180^{\circ}\). For triatomic molecules:

• They form a straight line
• Have no lone pairs on the central atom

Examples of linear triatomic molecules include:

• Carbon dioxide (CO2)
• Hydrogen cyanide (HCN)

In these molecules, the central atom is bonded to two other atoms that are directly opposite each other, creating a \(180^{\circ}\) bond angle.