Question

in a group of water molecules, hydrogen bonds form between ______.

a two hydrogen atoms in different water molecules

b the hydrogen atoms in a single water molecule

c the oxygen atoms in different water molecules

d the oxygen atom in one molecule and a hydrogen atom in another molecule

Explanation:

To determine where hydrogen bonds form in water molecules, we recall the structure of a water molecule ($\ce{H_2O}$). A water molecule has two hydrogen atoms covalently bonded to an oxygen atom. The oxygen atom is electronegative, creating a partial negative charge on oxygen and partial positive charges on the hydrogens. Hydrogen bonds form between a partially positive hydrogen (from one water molecule) and a partially negative atom (usually oxygen or nitrogen) from another molecule. In water, the hydrogen bond forms between the oxygen atom of one water molecule (which has a partial negative charge) and the hydrogen atom of another water molecule (which has a partial positive charge).

• Option a: Two hydrogen atoms are both partially positive, so they repel, and no hydrogen bond forms between them.
• Option b: Hydrogen atoms in a single water molecule are covalently bonded to oxygen, not forming hydrogen bonds with each other (they are part of the same molecule's covalent structure).
• Option c: Two oxygen atoms are both partially negative, so they repel, and no hydrogen bond forms between them.
• Option d: This matches the definition of a hydrogen bond in water: the oxygen (partial negative) of one molecule and the hydrogen (partial positive) of another molecule.

Answer:

d. the oxygen atom in one molecule and a hydrogen atom in another molecule