Atomic Structure

Science

The smallest particle of an element

Atom

The smallest particle of an element. Atom. An atom is the basic building block of matter, consisting of a nucleus surrounded by electrons.

The SI unit of the masses of particles in atoms

Atomic mass unit

The SI unit of the masses of particles in atoms atomic mass unit. An atomic mass unit amu is a small unit of mass used to measure the masses of particles in an atom, like protons and neutrons, where one amu is approximately 112 the mass of a carbon-12 atom.

Number of protons in an atom’s nucleus

Atomic number

Number of protons in an atoms nucleus. Atomic number. The atomic number is the number of protons in an atom's nucleus, which determines the type of element.

A negatively charged particle outside the nucleus of an atom

Electron

a negatively charged particle outside the nucleus of an atom. electron. Electrons are tiny particles that move around the nucleus of an atom and are responsible for electricity and chemical reactions.

An atom of the same element with a different number of neutrons

Isotope

An atom of the same element with a different number of neutrons. Isotope. Isotopes are variations of the same chemical element that have different numbers of neutrons in their nuclei.

The sum of neutrons and protons in an atom’s nucleus

Mass number

The sum of neutrons and protons in an atoms nucleus. mass number. The mass number is the total count of protons and neutrons that make up an atom's nucleus.

An uncharged particle in the nucleus of an atom

Neutron

An uncharged particle in the nucleus of an atom. Neutron. A neutron is a subatomic particle with no electric charge that resides in an atom's nucleus, helping to hold the nucleus together.

The center of an atom

Nucleus atom

The center of an atom nucleus. In simple terms, the nucleus is the tiny, dense core at the center of an atom that contains protons and neutrons.

A particle with a positive charge in an atom’s nucleus

Proton

A particle with a positive charge in an atom's nucleus. Proton. A proton is a tiny particle in the nucleus of an atom that carries a positive electrical charge.

An 1808 theory by John Dalton. the first theory to relate chemical changes to events at the atomic level

Daltons atomic theory

An 1808 theory by John Dalton, the first theory to relate chemical changes to events at the atomic level, Dalton's atomic theory. Dalton's atomic theory states that matter is made of small, indivisible particles called atoms.

A stream of electrons produced at the negative electrode of a cathode ray tube

Cathode ray

A stream of electrons produced at the negative electrode of a cathode ray tube. Cathode ray. A cathode ray is a beam of electrons traveling through a vacuum in a cathode ray tube.

The ability of an unstable nucleus to emit radiation

Radioactivity

The ability of an unstable nucleus to emit radiation. Radioactivity. It is the process by which unstable atomic nuclei release energy in the form of particles or electromagnetic waves.

A reaction that changes the composition of an atom’s nucleus

Nuclear reaction

A reaction that changes the composition of an atoms nucleus. Nuclear reaction. It is a process where the core of an atom changes, releasing a large amount of energy.

The breakdown of an unstable atomic nucleus, this releases particles and energy

Radioactive decay

The breakdown of an unstable atomic nucleus, this releases particles and energy. Radioactive decay. Radioactive decay is when an unstable atom loses energy and particles over time, turning into a different element.

An equation that shows the atomic number and mass number of every particle

Nuclear equation

An equation that shows the atomic number and mass number of every particle. Nuclear equation. A nuclear equation is a representation of a nuclear reaction showing the atomic numbers and mass numbers of the particles involved.