Chapter 2: Atoms and Molecules - The Chemical Basis of Life

Vocabulary flashcards covering key terms related to atoms, molecules, bonds, ions, pH, and basic chemical reactions from the lecture notes.

Element

A substance that cannot be decomposed into any simpler substance.

Atom

Smallest part of an element; consists of a nucleus (protons and neutrons) surrounded by electrons in shells.

Proton

Positively charged particle located in the nucleus.

Neutron

Electrically neutral particle located in the nucleus.

Electron

Negatively charged particle that orbits the nucleus in electron shells.

Nucleus

Center of the atom containing protons and neutrons.

Electron Shell

Regions around the nucleus where electrons are found; first shell holds 2 electrons, subsequent shells up to 8.

Valence Shell

Outermost electron shell; its electrons determine chemical behavior.

Valence Electrons

Electrons in the valence shell.

Atomic Number

Number of protons in the nucleus; defines the element and remains constant for that element.

Atomic Weight (Mass)

Total number of protons and neutrons in the nucleus.

Isotope

Atoms of the same element with different numbers of neutrons, hence different atomic weights.

Ion

An atom that has gained or lost electrons, giving it a net charge.

Cation

Positively charged ion.

Anion

Negatively charged ion.

Ionic Bond

Bond formed by transfer of electrons; attraction between oppositely charged ions.

Covalent Bond

Bond formed by sharing valence electrons; can be nonpolar or polar.

Hydrogen Bond

Weak attraction between a partially positive hydrogen and a negatively charged atom (often O or N); influences properties like water surface tension.

Polar Covalent Bond

Covalent bond with unequal sharing of electrons, creating partial charges.

Nonpolar Covalent Bond

Covalent bond with equal sharing of electrons.

Water (H2O)

A polar covalent molecule; excellent solvent for ionic or polar solutes.

pH

Measure of hydrogen ion concentration in a solution; scale from 0 to 14 with acidic

Acid

Substance that increases H+ concentration in solution (proton donor).

Base

Substance that reduces H+ concentration (proton acceptor) or yields OH-.  

Buffer

Substances that resist changes in pH; typically weak acids or bases.

Salt

Compound formed when the hydrogen of an acid is replaced by a cation; provides mineral ions.

Electrolyte

Salts, acids, and bases that dissociate in water to conduct electricity.

Nonelectrolyte

Covalent compounds that do not dissociate in water and do not conduct electricity.

Molecule

Two or more atoms bonded together.

Compound

Two or more elements bonded together in definite proportions.

Synthesis Reaction

Reaction where two or more reactants combine to form a larger product.

Decomposition Reaction

Reaction where a compound breaks down into simpler substances.

Exchange (Double Displacement) Reaction

Reaction where ions swap partners to form new compounds.

Reversible Reaction

Reaction that can proceed in both directions; energy carriers like ATP/ADP illustrate this.

Major life elements (4 most abundant by weight)

Carbon, Hydrogen, Oxygen, Nitrogen (among the ~13 essential elements) that make up most of living matter.