Introduction:

The shape of a molecule is determined by the arrangement of its atoms and the bonding between them. The two examples given, water (H2O) and carbon dioxide (CO2), have different structures due to the arrangement of their atoms and the type of bonding involved.

Water molecule:

Structure:
- A water molecule consists of two hydrogen atoms bonded to one oxygen atom.
- The oxygen atom is located in the center, with the two hydrogen atoms bonded to it.
- The molecule has a bent or V-shaped structure, with the oxygen atom at the vertex of the V and the hydrogen atoms forming the arms.
- The angle between the two arms of the V is approximately 104.5 degrees.

Bonding:
- The oxygen atom in water has six valence electrons, while each hydrogen atom has one valence electron.
- Oxygen needs two additional electrons to complete its octet, while each hydrogen atom needs one additional electron.
- In water, the oxygen atom shares two electrons with each hydrogen atom, resulting in four shared electrons in total.
- These shared electrons form two covalent bonds, one between oxygen and each hydrogen atom.

Reason for bent structure:
- The reason for the bent structure of water lies in the arrangement of its electron pairs.
- Water has two lone pairs of electrons on the oxygen atom, in addition to the two shared electron pairs.
- These lone pairs exert greater repulsive forces on each other compared to shared electron pairs.
- As a result, the lone pairs push the shared pairs away from each other, causing the bond angle to deviate from the ideal 180 degrees.
- This repulsion between the lone pairs and shared pairs leads to a bent shape in the water molecule.

Carbon dioxide molecule:

Structure:
- A carbon dioxide molecule consists of one carbon atom bonded to two oxygen atoms.
- The carbon atom is located in the center, with the two oxygen atoms bonded to it.
- The molecule has a linear structure, with the carbon atom in the middle and the two oxygen atoms on either side.

Bonding:
- The carbon atom in carbon dioxide has four valence electrons, while each oxygen atom has six valence electrons.
- Carbon needs four additional electrons to complete its octet, while each oxygen atom needs two additional electrons.
- In carbon dioxide, one carbon atom shares two electrons with each oxygen atom, resulting in four shared electrons in total.
- These shared electrons form two double bonds, one between carbon and each oxygen atom.

Reason for linear structure:
- The linear structure of carbon dioxide is due to the arrangement of its electron pairs.
- Carbon dioxide has no lone pairs of electrons on the carbon atom.
- The repulsion between the shared electron pairs is minimal, as there are no additional electron pairs pushing them apart.
- Consequently, the bond angle between the carbon and oxygen atoms is 180 degrees, resulting in a linear shape for the molecule.

Conclusion:

The difference in structure between water and carbon dioxide arises from the arrangement of their electron pairs. Water's bent structure is a result of the repulsion between lone pairs and shared pairs, leading to a deviation from the ideal bond angle. On the other hand, carbon dioxide's linear structure is due to the absence of lone pairs and minimal repulsion between the shared electron pairs. These