Hydrogen Bonding

Hydrogen Bonds (Review of Covalent Bonds)

Covalent Bonding

• Sharing of electrons between molecules.

• Atoms sharing electrons achieve complete outer shells.

• One of the strongest types of chemical bonds, requiring significant energy to break.

Hydrogen Bonding

• A weaker bond occurring between two molecules.

• Results from electrostatic attraction.

• Forms between a hydrogen atom in one molecule and an atom of oxygen, nitrogen, or fluorine in another molecule.

• Water molecules are bonded by hydrogen bonds.

Polarities Role in Hydrogen Bonding Between Water Molecules

• In a water molecule, the covalent bond between oxygen and hydrogen atoms shares electrons unequally:

  • Oxygen atom: partially negative charge.

  • Hydrogen atoms: partially positive charges.

• Molecules with partial charges are polar.

• Positive hydrogen atoms of one water molecule attract negative oxygen atoms of another, leading to hydrogen bond formation.

Hydrogen Bonding Properties of Water

Universal Solvent

• Hydrogen bonds are dynamic, continually forming and breaking.

• Water acts as a solvent, dissolving many substances:

  • Partial charges enable interactions with charged ions (like salt) and covalent substances (like glucose).

Density of Water

• As water cools and approaches freezing, molecular movement decreases, allowing hydrogen bonds to strengthen.

  • Colder water becomes denser than warmer water.

• Upon freezing, water forms a lattice structure, spacing molecules apart, making ice less dense than liquid water.

Specific Heat Capacity

• Requires substantial heat to raise water's temperature due to hydrogen bonding.

• This property enables water to act as a temperature buffer, moderating the planet’s climate.

  • Oceans can store significant heat before temperature changes, creating mild coastal climates.