A&P Chapter 2: Atoms, Water, pH, and Chemical Reactions

Atom

The smallest unit of an element that retains its unique chemical properties.

Proton

A positively charged subatomic particle located in the nucleus of an atom.

Neutron

A subatomic particle with no electrical charge located in the nucleus of an atom.

Electron

A negatively charged subatomic particle found orbiting outside the atomic nucleus.

Atomic Number

The total number of protons in an atom, which uniquely determines the identity of an element.

Atomic mass

The total count of protons and neutrons within an atom's nucleus.

Valence Electrons

Electrons residing in the outermost energy level that participate in bonding and determine chemical behavior.

Bohr Planetary Model

An atomic model depicting electrons orbiting the nucleus in fixed, concentric energy shells.

Quantum Mechanical Model

An atomic model describing electrons as existing within probability regions called electron clouds.

Isotope

A variant form of an element containing the same number of protons but a different number of neutrons.

Radioisotope

An unstable isotope that spontaneously decays over time, emitting ionizing radiation.

Ionization

The process of transferring electrons from one atom to another to form charged particles.

Anion

A negatively charged ion formed when an atom gains one or more electrons.

Cation

A positively charged ion formed when an atom loses one or more electrons.

Potential Energy

Stored energy not currently performing work, such as chemical energy within molecular bonds.

Kinetic Energy

Energy associated with motion, such as heat, molecular vibration, or ion movement.

Decomposition Reaction

A chemical reaction in which a larger molecule breaks down into smaller units, represented as $\text{AB} \rightarrow \text{A} + \text{B}$.

Synthesis Reaction

A chemical reaction in which smaller reactants combine to form a larger product, represented as $\text{A} + \text{B} \rightarrow \text{AB}$.

Exchange Reaction

A chemical reaction in which two molecules swap atoms or groups of atoms, represented as $\text{AB} + \text{CD} \rightarrow \text{AC} + \text{BD}$.

Reversible Reaction

A reaction that can proceed in both forward and reverse directions, indicated by the symbol $\rightleftharpoons$.

Chemical Equilibrium

The state reached when the ratio of products to reactants remains constant over time.

Law of Mass Action

The principle stating that the direction of a reversible reaction depends on the relative concentrations of reactants and products.

Physical Half-Life

The time required for $50\%$ of a radioisotope's atoms to undergo radioactive decay.

Biological Half-Life

The time required for $50\%$ of a radioactive substance to be eliminated from the body.

Ionizing Radiation

High-energy radiation capable of ejecting electrons from atoms, creating free radicals and biological damage.

Marie Curie

Pioneering scientist who coined the term radioactivity and discovered polonium and radium.

Sievert (Sv)

The standard unit used to measure biological dosage and harm from radiation exposure.