A1.1.2 Hydrogen bonds as a consequence of the polar covalent bonds within water molecules Notes

The Structure of a Water Molecule

1. A water molecule consists of one oxygen atom and two hydrogen atoms bonded together by covalent bonds.
2. Covalent bonds form when atoms share electrons.
3. However, in water, the sharing is unequal because oxygen is more electronegative than hydrogen.

Polarity: Unequal Charge Distribution

1. Because oxygen pulls electrons closer:
   1. The oxygen atom develops a partial negative charge (δ−).
   2. The hydrogen atoms develop partial positive charges (δ+).
2. This uneven charge distribution makes water a polar molecule, it has a positive end (hydrogen side) and a negative end (oxygen side).

Polarity Enables Hydrogen Bonding

1. This polarity is what allows hydrogen bonds to form between water molecules:
   1. The δ+ hydrogen of one molecule is electrostatically attracted to the δ− oxygen of a neighboring molecules.
   2. Because opposite charges attract, these polar regions create weak intermolecular attractions.
   3. These attractions are hydrogen bonds.

How to Draw a Water Molecule

To show the structure and polarity of water:

1. Draw the Atoms:
   1. Place one oxygen atom (O) in the center.
   2. Add two hydrogen atoms (H) on either side, positioned at an angle of approximately 104.5° to each other, reflecting the molecule's bent shape.
2. Show the Bonds:
   1. Draw a single covalent bond (-) between each hydrogen atom and the oxygen atom. These represent shared electrons.
3. Indicate Partial Charges:
   1. Label the oxygen atom with a partial negative charge (δ⁻) because it is more electronegative and pulls shared electrons closer.
   2. Label each hydrogen atom with a partial positive charge (δ⁺) because electrons are drawn away from them.