Question

18 ccc cause and effect why can molecules made of three atoms have a bent or linear shape?

Explanation:

To determine the shape of a triatomic molecule (3 - atom molecule), we use the VSEPR (Valence - Shell Electron - Pair Repulsion) theory. The central atom's electron - pair geometry (including bonding and non - bonding pairs) dictates the molecular shape.

• Linear shape: When the central atom has two bonding pairs and no lone (non - bonding) pairs of electrons, the electron - pair geometry is linear. For example, in $\ce{CO_2}$, the carbon atom is the central atom. It forms two double bonds with oxygen atoms, and there are no lone pairs on the carbon atom. The bond angle is $180^{\circ}$, so the molecule is linear.
• Bent shape: When the central atom has two bonding pairs and one or two lone pairs of electrons, the molecular shape is bent. For example, in $\ce{H_2O}$, the oxygen atom is the central atom. It has two bonding pairs (with hydrogen atoms) and two lone pairs of electrons. The lone pairs repel the bonding pairs, reducing the bond angle from the ideal tetrahedral angle ($109.5^{\circ}$) to about $104.5^{\circ}$, resulting in a bent shape. Another example is $\ce{SO_2}$, where the sulfur atom (central atom) has two bonding pairs and one lone pair, leading to a bent molecular shape.

In summary, the presence or absence of lone pairs on the central atom, along with the number of bonding pairs, determines whether a triatomic molecule is linear (no lone pairs on the central atom, two bonding pairs) or bent (lone pairs on the central atom along with two bonding pairs).

Answer:

Triatomic molecules can have a linear or bent shape due to the VSEPR theory. A linear shape occurs when the central atom has 2 bonding pairs and 0 lone pairs (e.g., $\ce{CO_2}$). A bent shape occurs when the central atom has 2 bonding pairs and 1 or 2 lone pairs (e.g., $\ce{H_2O}$, $\ce{SO_2}$), as lone pairs repel bonding pairs and alter the molecular geometry.