Chapter 2 – The Chemical Basis of Life I: Atoms, Molecules, and Water

Vocabulary flashcards covering key terms from Chapter 2: Atoms, Bonds, Reactions, Water, and pH and Buffers.

Atom

The smallest functional unit of matter; cannot be broken down into other substances by ordinary chemical or physical means.

Element

A pure substance made up of only 1 kind of atom.

Molecule

Two or more atoms bonded together.

Nucleus

The center of an atom that contains protons and neutrons.

Proton

A positively charged subatomic particle located in the atomic nucleus.

Neutron

An electrically neutral subatomic particle located in the atomic nucleus.

Electron

A negatively charged subatomic particle found in orbitals around the nucleus; negligible mass compared to protons/neutrons.

Orbital

A three‑dimensional region of space where an electron is likely to be found; each orbital holds up to 2 electrons.

Electron shell

Energy levels that contain orbitals; shells are numbered by distance from the nucleus.

Valence electrons

Electrons in the outermost shell that can participate in chemical bonds.

Atomic number

The number of protons in an atom; unique to each element and equals the number of electrons in a neutral atom.

Periodic table

A table that arranges elements by atomic number and electron shells; rows relate to electron shells, columns to valence electrons.

Dalton (Da) / unified atomic mass unit

A unit of atomic/molecular mass; 1 Da ≈ 1/12 the mass of a carbon-12 atom.

Mole

The amount of substance containing 6.022 × 10^23 particles; the mass in grams of a substance equals its molar mass.

Isotope

Forms of an element with the same atomic number but different numbers of neutrons; different atomic masses.

Oxygen, Carbon, Hydrogen, Nitrogen

The four elements that typically make up about 95% of living matter's mass.

Covalent bond

A bond formed when atoms share electrons to fill their outer shells.

Polar covalent bond

A covalent bond where electrons are shared unequally due to differences in electronegativity, creating partial charges.

Nonpolar covalent bond

A covalent bond where electrons are shared equally, with no significant charge difference across the molecule.

Electronegativity

A measure of an atom’s ability to attract electrons; differences lead to polar vs nonpolar bonds.

Hydrogen bond

A weak attraction between a hydrogen atom with a partial positive charge and an electronegative atom/ molecule; collectively strong.

Van der Waals dispersion forces

Weak, temporary attractions between molecules due to transient dipoles; can be collectively significant.

Ionic bond

Attractive force between positively charged cations and negatively charged anions; salts form from these bonds.

Ion

An atom or molecule with a net electric charge from gain or loss of electrons; includes cations and anions.

Cation

An ion with a positive charge.

Anion

An ion with a negative charge.

Hydrophilic

Substances that dissolve in water or interact well with water due to charge or polarity.

Hydrophobic

Substances that do not dissolve in water; typically nonpolar.

Amphipathic

Molecules with both polar (hydrophilic) and nonpolar (hydrophobic) regions.

Micelle

A spherical arrangement of amphipathic molecules in water, with hydrophobic tails inward and polar heads outward.

Bilayer

A double-layered arrangement of amphipathic molecules forming a membrane, such as cell membranes.

Solvent

The liquid in a solution that dissolves solutes.

Solute

The substance dissolved in a solvent.

Solution

A homogeneous mixture of solute(s) dissolved in a solvent.

Molarity (M)

A measure of solute concentration; moles of solute per liter of solution (mol/L).

State of water

Water exists as solid (ice), liquid (water), and gas (water vapor).

Specific heat

The amount of heat needed to raise the temperature of 1 g of a substance by 1°C.

Heat of fusion

Energy required to melt a solid.

Heat of vaporization

Energy required to convert a liquid to a gas.

pH

A measure of H+ (hydrogen ion) concentration; pH = -log10[H+].

Acid

A substance that donates H+ in solution, increasing [H+]; can be strong or weak.

Base

A substance that accepts H+ in solution, decreasing [H+]; can release OH- or bind H+; can be strong or weak.

Buffer

A substance or system that resists pH changes by absorbing or releasing H+ to neutralize added acid or base.

Carbonic acid/bicarbonate buffer

A common biological buffer system that helps maintain stable pH in body fluids.

pH scale relationships

pH is inversely related to [H+]; moving up the pH scale corresponds to lower H+ concentration.