Matter and Radiation – Inside the Atom & Nuclear Stability

Vocabulary flashcards covering atomic structure, isotopes, specific charge, nuclear forces, and radioactive emissions from the provided lecture notes.

Atom

The smallest unit of an element, consisting of a positively-charged nucleus surrounded by negatively-charged electrons.

Nucleus

The dense central region of an atom containing protons and neutrons and holding almost all of the atom’s mass.

Proton

A positively-charged nucleon found in the nucleus; its charge is +1.60 × 10⁻¹⁹ C and its relative mass is 1.

Neutron

An uncharged nucleon located in the nucleus with a relative mass of 1.

Electron

A negatively-charged particle orbiting the nucleus; charge −1.60 × 10⁻¹⁹ C and relative mass 0.0005.

Nucleon

A collective term for the particles (protons or neutrons) that reside in an atomic nucleus.

Isotope

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

Atomic Number (Z)

The number of protons in an atom’s nucleus; identifies the element.

Nucleon Number (Mass Number, A)

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

Nuclide

A specific nucleus identified by its atomic number and mass number (e.g., ²³⁸₉₂U).

Specific Charge

The charge-to-mass ratio of a particle, calculated as charge divided by mass (C kg⁻¹).

Ion

An atom (or group) that has gained or lost electrons, giving it a net electric charge.

Rutherford Alpha-Scattering

Historic experiment showing atoms have a small, massive, positively-charged nucleus.

Electrostatic Force

The attractive or repulsive force between electrically charged particles; holds electrons around the nucleus.

Strong Nuclear Force

The short-range (≈0.5–4 fm) force that binds protons and neutrons in the nucleus, overcoming electrostatic repulsion.

Femtometre (fm)

A unit of length equal to 10⁻¹⁵ m, roughly the size scale of atomic nuclei.

Stable Isotope

A nuclide whose nucleus does not spontaneously disintegrate.

Radioactive Decay

The spontaneous transformation of an unstable nucleus accompanied by emission of radiation.

Alpha Particle (⁴₂α)

A helium-4 nucleus consisting of two protons and two neutrons, emitted during alpha decay.

Alpha Radiation

Ionising radiation composed of alpha particles; emission decreases A by 4 and Z by 2 in the parent nucleus.

Beta Minus Particle (β⁻)

An electron emitted from the nucleus when a neutron converts into a proton during beta minus decay.

Scanning Tunnelling Microscope (STM)

An instrument capable of imaging individual atoms by measuring tunnelling current.