Covalent Bonds and Water Properties

Overview

This lecture explains covalent bonds, focusing on bond polarity, electronegativity, and the unique properties of water due to hydrogen bonding.

Covalent bonds form when atoms share electrons.
Oxygen has a higher electronegativity (ability to attract electrons) than hydrogen.
Electronegativity difference causes shared electrons to spend more time near the oxygen nucleus.

Polar covalent bonds have unequal sharing of electrons, creating partial positive and negative poles.
Non-polar covalent bonds have equal sharing of electrons and do not create poles.
Examples of non-polar molecules include N₂, O₂, F₂, and CO₂.
Polar covalent bonds cause dipoles and intermolecular attractions.

Ionic bonds occur when electron transfer is so complete that atoms become charged ions.
The attraction between oppositely charged ions forms ionic bonds.

Hydrogen chloride (HCl) is a polar covalent compound; chlorine is more electronegative and gains a partial negative charge.
Partial charges are represented by the Greek letter delta (δ+ for positive, δ- for negative).

Water (H₂O) is a polar molecule; oxygen is partially negative, hydrogens are partially positive.
Water’s polarity allows it to dissolve many substances and attracts other water molecules.
Hydrogen bonds are weak attractions between a partially positive hydrogen and a partially negative atom (like oxygen).
Hydrogen bonds are much weaker than covalent or ionic bonds but are crucial for water’s properties like surface tension and droplet formation.

Covalent bond — a chemical bond where atoms share electron pairs.
Electronegativity — the ability of an atom to attract shared electrons.
Polar covalent bond — a bond where electrons are shared unequally, creating partial charges (dipoles).
Non-polar covalent bond — a bond with equal sharing of electrons, creating no poles.
Ionic bond — a bond formed by the transfer of electrons and attraction between charged ions.
Dipole — a molecule with partial positive and negative charges at opposite ends.
Intermolecular forces — weak attractions between molecules.
Hydrogen bond — a weak attraction between a hydrogen atom and a partially negative atom.