Water's Molecular Structure and Properties

Overview

This lecture explains the molecular structure of water, why it is polar, how hydrogen bonds form between water molecules, and how these bonds give water its unique properties essential for life.

Structure of Water

• Water (H₂O) consists of two hydrogen atoms and one oxygen atom connected by covalent bonds.
• The molecule has a tetrahedral shape due to two lone pairs of electrons on the oxygen atom.
• The hydrogen atoms are not opposite each other because lone electron pairs repel the bonded atoms.

Polarity and Electronegativity

• Oxygen is highly electronegative, meaning it attracts electrons more than hydrogen does.
• This unequal sharing causes a partial negative charge near oxygen and a partial positive charge near hydrogens.
• The partial charges make water a polar molecule.

Hydrogen Bonding Between Water Molecules

• The partial positive charge on hydrogen is attracted to the partial negative charge on oxygen of another water molecule.
• This attraction is called a hydrogen bond.
• Hydrogen bonds are weaker than covalent bonds but strong enough to hold water molecules together.

Properties and Importance of Hydrogen Bonding

• Hydrogen bonding causes water's high boiling point, heat capacity, cohesion, and surface tension.
• These bonds allow water to regulate temperature and dissolve polar molecules, making it an effective solvent.
• The fluidity of water comes from hydrogen bonds constantly forming, breaking, and reforming.

Key Terms & Definitions

• Covalent bond — a bond where two atoms share a pair of electrons.
• Electronegativity — an atom’s tendency to attract electrons in a bond.
• Polar molecule — a molecule with opposite partial charges on different ends.
• Lone pair — a pair of valence electrons not involved in bonding.
• Hydrogen bond — a weak attraction between a partially positive hydrogen and a partially negative atom (usually oxygen or nitrogen).

Action Items / Next Steps

• Watch the next video or read the article on "Hydrogen bonds in water."
• Review the concepts of polarity and intermolecular forces for upcoming lessons.