Final answer:
Adding a single-bonded atom to a molecule affects the electron distribution and may alter the molecular geometry, as each atom seeks to fulfill the octet rule or duet rule for hydrogen. Single bonds have a more subtle effect compared to multiple bonds and lone pairs of electrons that take up more space.
Step-by-step explanation:
When a single-bonded atom is added to a molecule, it affects the existing atoms' electron configuration and molecular shape. Adding a single bond requires placing a pair of electrons between adjacent atoms. For example, in water (H₂O), there is a bonding pair of electrons between the oxygen and each hydrogen atom.
Each atom in a molecule seeks to fulfill the octet rule, aiming for eight electrons in their valence shell (with the exception of hydrogen, which aims for two).
When you add single-bonded atoms to the molecule, electrons are redistributed to ensure that each atom meets the octet rule. Lone pairs of electrons may be present on terminal atoms, which could potentially be used to form multiple bonds with the central atom if necessary to achieve a full octet.
However, the addition of a single-bonded atom can influence the molecule's geometry. While multiple bonds and lone pairs of electrons take up more space and can reduce bond angles, single bonds add less electron density around the central atom and thus have a more subtle effect on molecular shape.