Chemistry of Life – Lecture 1 Vocabulary

A collection of key vocabulary terms and concise definitions drawn from Dr. Lebani’s Chemistry of Life Lecture 1.

Atom

The smallest unit of an element that retains the chemical and physical properties of that element.

Element

A pure substance made of only one kind of atom that cannot be broken down by ordinary chemical means.

Carbon, Hydrogen, Oxygen, Nitrogen (CHON)

The four elements that together constitute more than 96 % of the mass of living organisms.

Molecule

Two or more atoms chemically bonded together in fixed ratios.

Compound

A molecule composed of two or more different elements, possessing properties distinct from its constituent atoms.

Proton

A positively charged sub-atomic particle located in the nucleus of an atom.

Neutron

An electrically neutral sub-atomic particle found in the atomic nucleus.

Electron

A negatively charged sub-atomic particle that orbits the atomic nucleus in discrete energy levels.

Dalton (Da)

A unit of atomic mass equal to 1.66 × 10⁻²⁴ g, approximately the mass of a proton or neutron.

Isotope

Atoms of the same element that contain different numbers of neutrons.

Energy Level (Electron Shell)

A region around an atomic nucleus where electrons are likely to be found; determines an atom’s chemical reactivity.

Valence Electrons

Electrons in the outermost energy level of an atom that participate in chemical bonding.

Chemical Bond

An interaction that holds two atoms together, formed by the transfer or sharing of electrons.

Ionic Bond

An electrostatic attraction between oppositely charged ions formed after complete transfer of valence electrons (metal + non-metal).

Ion

An atom or molecule that has gained or lost electrons, acquiring a net electric charge.

Covalent Bond

A chemical bond in which two atoms share one or more pairs of valence electrons (commonly between non-metals).

Nonpolar Covalent Bond

A covalent bond in which electrons are shared equally between the bonded atoms.

Polar Covalent Bond

A covalent bond with unequal sharing of electrons, resulting in partial positive and negative charges on the atoms.

Hydrogen Bond

A weak intermolecular attraction between a hydrogen atom already bonded to a highly electronegative atom and another electronegative atom with a lone pair.

Van der Waals Forces

Weak, short-range attractions between non-polar molecules or regions caused by transient charge fluctuations.

London Dispersion Force

A type of van der Waals attraction arising from temporary dipoles in atoms or non-polar molecules.

Dipole-Dipole Interaction

A van der Waals force between permanent partial charges of polar molecules.

Water (H₂O)

A polar molecule whose extensive hydrogen bonding gives it unique solvent, cohesion, adhesion, and temperature-stabilizing properties.

Cohesion

The tendency of water molecules to stick to one another via hydrogen bonding.

Adhesion

The attraction between water molecules and other polar or charged surfaces.

Specific Heat Capacity

The amount of heat required to raise the temperature of a substance; water’s high value stabilizes temperatures.

Density Anomaly of Water

Water is less dense as ice than as liquid due to the open lattice of hydrogen bonds in ice.

Ionization of Water

The spontaneous dissociation of water into equal concentrations of H⁺ and OH⁻ ions.

pH

A logarithmic measure of hydrogen-ion concentration defined as –log₁₀[H⁺].

Acid

A substance that donates protons (H⁺) in solution, increasing [H⁺] and lowering pH.

Base (Alkali)

A substance that accepts protons or donates OH⁻ in solution, decreasing [H⁺] and raising pH.

Buffer

A mixture of a weak acid and its conjugate base (or vice versa) that resists changes in pH by reversibly binding H⁺ or OH⁻.

Bicarbonate Buffer System

The blood’s principal buffer comprising carbonic acid (H₂CO₃) and bicarbonate ion (HCO₃⁻) that moderates pH via reversible reactions with CO₂.

Carbonic Acid (H₂CO₃)

A weak acid formed when CO₂ dissolves in water; key component of the bicarbonate buffer system.

Bicarbonate Ion (HCO₃⁻)

The conjugate base of carbonic acid that binds excess H⁺ to regulate blood pH.

Hydrophilic

Describes polar or charged molecules that readily interact with water.

Hydrophobic

Describes non-polar molecules that repel water and do not dissolve in it.

Salt

An ionic compound that releases ions other than H⁺ or OH⁻ when dissolved in water.