The basic arrangement of an atom consisting of a central nucleus containing protons and neutrons, surrounded by electrons in energy levels. The radius is approximately 1 × 10⁻¹⁰ meters.

Negatively charged particle that orbits the nucleus in energy levels. Has negligible mass (1/2000 of a proton) and a relative charge of -1.

Positively charged particle found in the nucleus. Has a relative mass of 1 and a relative charge of +1.

Neutral particle found in the nucleus. Has a relative mass of 1 and no electrical charge.

The central part of an atom containing protons and neutrons. Contains almost all the mass of the atom and has a positive charge.

Fixed distances from the nucleus where electrons orbit. First level holds 2 electrons, second and third levels can each hold 8 electrons.

Atoms of the same element with same number of protons but different numbers of neutrons. Have same atomic number but different mass numbers.

Model of the atom with a dense, positively charged nucleus containing protons and neutrons, surrounded by electrons in orbit. Proposed by Rutherford based on his scattering experiment.

Early model of the atom proposed by J.J. Thomson where negatively charged electrons were embedded in a positively charged sphere, like plums in a pudding.

Experiment where alpha particles were fired at gold foil. Most passed through, but some were deflected at large angles, leading to the discovery of the nuclear model.

The number of protons in an atom's nucleus. Determines the element's identity and equals the number of electrons in a neutral atom.

The total number of protons and neutrons in an atom's nucleus. Can be calculated by adding the number of protons and neutrons together.

Process where an atom gains or loses electrons to form an ion. Losing electrons creates positive ions, gaining electrons creates negative ions.

Energy that can be absorbed or emitted by electrons, causing them to move between energy levels. Can cause ionization by providing enough energy for electrons to escape atoms.

The deflection of alpha particles by gold foil in Rutherford's experiment. Led to the discovery that atoms have a small, dense, positively charged nucleus.