Final answer:
The first carbon in glucose is double bonded to oxygen to provide that carbon atom with a stable octet of electrons. The double bond is more polar than carbon-to-oxygen single bonds due to greater electronegativity of oxygen. The remaining carbons bond with OH groups to fulfill the hydrogen to carbon ratio and stabilize each carbon's electronic structure.
Step-by-step explanation:
The reason the first carbon in glucose is double bonded to an oxygen while the other five carbons are bonded to an OH group (hydroxyl group) lies in the molecular structure that ensures a stable electronic arrangement. Carbon atoms need to have an octet of electrons to be stable. Initially, carbon has only six electrons, which makes it unstable. By forming a double bond with oxygen, carbon can achieve an octet. Oxygen contributes one of its lone pairs to make a third bond with carbon. This double bond formation between carbon and oxygen results in both atoms achieving a stable electronic configuration.
The double bond is polar because the electronegative oxygen atom has a greater attraction for the bonding electron pairs than the carbon atom, leading to a partial positive charge on carbon and a partial negative charge on oxygen. In contrast, the other carbons are bonded to OH groups because each carbon atom can achieve a full octet by forming single bonds with other atoms, and the OH groups fulfill the valencies while maintaining the required hydrogen to carbon ratio in glucose's molecular formula, which is C6H12O6.