S1.2 The nuclear atom Notes

Atom

The fundamental building block of matter, composed of protons, neutrons, and electrons.

Proton

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

Neutron

A neutral subatomic particle found in the nucleus of an atom.

Electron

A negatively charged subatomic particle that orbits the nucleus of an atom.

Nucleus

The dense, positively charged core of an atom containing protons and neutrons.

Atomic Number (Z)

The number of protons in the nucleus of an atom, which defines the element.

Mass Number (A)

The total number of protons and neutrons in an atomic nucleus.

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons.

Ion

An atom or group of atoms that has gained or lost electrons, resulting in a net electrical charge.

Cation

An ion with a positive charge, formed when an atom loses electrons.

Anion

An ion with a negative charge, formed when an atom gains electrons.

Relative Atomic Mass

A weighted average of the masses of an element's isotopes based on their natural abundances.

Relative Abundance

The percentage of a specific isotope of an element present in a naturally occurring sample.

Orbital

Regions of space around the nucleus where electrons are likely to be found.

Isotopic Abundance

The natural occurrence of isotopes of an element in a sample.

Chemical Symbol

A notation used to represent an element, usually consisting of one or two letters.

Nucleons

Collective term for the protons and neutrons in an atomic nucleus.

Density

The mass per unit volume of a substance, which can vary between isotopes.

Boiling Point

The temperature at which a substance transitions from a liquid to a gas; can vary between isotopes.

Melting Point

The temperature at which a solid transitions to a liquid; can vary between isotopes.

Stable Isotope

An isotope that does not undergo radioactive decay.

Radioactive Isotope

An isotope that is unstable and decays over time, emitting radiation.

Chlorine-35

An isotope of chlorine with 17 protons and 18 neutrons.

Chlorine-37

An isotope of chlorine with 17 protons and 20 neutrons.

Protium

The most common isotope of hydrogen, with 1 proton and no neutrons.

Deuterium

A heavier isotope of hydrogen, with 1 proton and 1 neutron.

Tritium

A radioactive isotope of hydrogen, with 1 proton and 2 neutrons.

Uranium-235

An isotope of uranium used in nuclear reactors and weapons.

Uranium-238

A more abundant isotope of uranium, less useful for nuclear reactions.

Electron Configuration

The distribution of electrons in an atom's orbitals.

Chemical Behavior

The way a substance interacts in a chemical reaction, largely determined by its electron configuration.

Stable Configuration

An arrangement of electrons resulting in lower energy and greater stability in atoms.

Atomic Mass Unit (amu)

A unit of mass used to express atomic and molecular weights.

Mol

A quantity in chemistry that represents 6.022 x 10^23 particles of a substance.

Half-life

The time required for half the quantity of a radioactive isotope to decay.

Decaying Isotope

An isotope that undergoes radioactive decay transforming into a different element or isotope.

Fission

The splitting of a heavy atomic nucleus into smaller nuclei, releasing energy.

Fusion

The process of combining light atomic nuclei to form a heavier nucleus, releasing energy.

Alpha Particle

A type of radiation consisting of two protons and two neutrons.

Beta Particle

A high-energy, high-speed electron or positron emitted during radioactive decay.

Gamma Ray

Electromagnetic radiation emitted during radioactive decay in high-energy states.

Nuclear Reaction

A process that alters the energy or structure of atomic nuclei.

Thermonuclear Reaction

A nuclear reaction that occurs at extremely high temperatures, typically in stars.

Chemical Equation

A symbolic representation of a chemical reaction.

Copper-63

An isotope of copper that has 29 protons and 34 neutrons.

Copper-65

An isotope of copper that has 29 protons and 36 neutrons.