Chapter 2 – The Chemical Basis of Life I: Atoms, Molecules, and Water (Vocabulary Flashcards)

Vocabulary flashcards covering key terms from chapters 2.1–2.5: atoms, bonds, reactions, water properties, pH and buffers.

Atom

The smallest functional unit of matter that forms all chemical substances; cannot be broken down by ordinary chemical or physical means.

Element

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

Molecule

Two or more atoms bonded together.

Compound

A molecule that contains different kinds of atoms.

Proton

Positively charged subatomic particle located in the atomic nucleus.

Neutron

Electrically neutral subatomic particle located in the atomic nucleus.

Electron

Negatively charged subatomic particle found in orbitals around the nucleus.

Nucleus

Center of an atom containing protons and neutrons.

Orbital

Three-dimensional region around the nucleus where electrons are found; each orbital holds up to 2 electrons.

Electron shell

A group of orbitals in a shell; shells are numbered and have characteristic energy.

Valence electrons

Electrons in the outermost shell that participate in bonds.

Atomic number

Number of protons in an atom; defines the element and equals the number of electrons in a neutral atom.

Isotopes

Variants of an element with the same atomic number but different neutron number; some are radioisotopes.

Dalton (Da)

Unit of atomic mass; 1 Da = 1/12 the mass of a carbon-12 atom.

Mole

Amount of substance containing 6.022 x 10^23 particles; the mass in grams equals the atomic or molecular weight.

Cation

Positively charged ion.

Anion

Negatively charged ion.

Ionic bond

Bond formed by electrostatic attraction between oppositely charged ions; salts like NaCl.

Covalent bond

Bond formed when atoms share electrons to fill outer shells; can be single, double, or triple.

Single bond

One shared pair of electrons between two atoms.

Double bond

Two shared pairs of electrons between two atoms.

Triple bond

Three shared pairs of electrons between two atoms.

Polar covalent bond

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

Nonpolar covalent bond

Covalent bond where electrons are shared equally; no partial charges.

Electronegativity

A measure of an atom's ability to attract electrons within a bond.

Hydrogen bond

Weak attraction between a hydrogen in a polar bond and an electronegative atom on another molecule; important in proteins and DNA networks.

van der Waals dispersion forces

Very weak, temporary attractions between nonpolar molecules due to fluctuating electron distribution.

Hydrophilic

Substances that readily dissolve in water; polar or charged.

Hydrophobic

Substances that do not dissolve in water; nonpolar.

Amphipathic

Molecules with both polar and nonpolar regions; can form micelles or bilayers in water.

Micelle

Spherical aggregates formed by amphipathic molecules in aqueous environments.

Solute

Substance dissolved in a solvent.

Solvent

Liquid in which solutes are dissolved.

Solution

A homogeneous mixture of solutes in a solvent.

Molarity

Moles of solute per liter of solution (mol/L).

Water states

Water exists as solid ice, liquid water, and water vapor; changes involve energy.

pH

Measure of hydrogen ion concentration; pH = -log10[H+].

Acid

Substance that donates H+ in solution; increases [H+].

Base

Substance that accepts H+ in solution; decreases [H+].

Buffer

Substance that minimizes pH changes by absorbing or releasing H+; carbonic acid/bicarbonate buffer is common in body fluids.

Carbonic acid/bicarbonate buffer system

A major buffering system in body fluids that maintains pH by shifting between H2CO3 and HCO3-.

Hydroxide ion

OH−; a negatively charged ion produced when water dissociates.

Hydrogen ion

H+; a positively charged ion produced when water dissociates.

Equilibrium

State where the forward and reverse reaction rates are equal; many biological reactions are coupled and do not reach true equilibrium.

Four essential elements

Oxygen, carbon, hydrogen, and nitrogen; make up about 95% of most living organisms' mass.