explain why the hydrogen atoms in a hydrogen gas molecule form nonpolar covalent bonds but the oxygen and hydrogen atoms in water molecules form polar covalent bonds

A non-polar covalent bond contains electrons that are shared equally between atoms. This occurs when the electronegativity difference between the atoms in the bond is zero or very small. You can find the electronegativity values for each atom by searching online or looking in your textbook. The electronegativity value of each H atom in the molecule is 2.2. The difference between the electronegativity values of two H atoms is 2.2 - 2.2 = 0. Therefore, the bond between the two H atoms in the molecule is a non-polar bond.

A polar covalent bond contains electrons that are shared unequally between atoms. This occurs when the electronegativity difference between the atoms in the bond is between 0.3 and 1.7. The electronegativity value of O is 3.5. The electronegativity value of H is 2.2. The difference between the electronegativity values of O and H is 3.5 - 2.2 = 1.3. Therefore, the bonds between the O atom and each H atom in the molecule are polar covalent bonds.