Introduction to Atomic Theory and Key Discoveries

This collection of flashcards covers key vocabulary related to atomic theory, the historical development of atomic models, and significant experiments that contributed to our understanding of atomic structure.

Atomic Theory

The scientific theory that matter is composed of small, indivisible particles called atoms.

Indivisible

A term derived from the Greek word 'atomos', meaning uncuttable, used to describe the nature of atoms as fundamental building blocks of matter.

Law of Conservation of Mass

A principle stating that matter cannot be created or destroyed in an isolated system; it can change forms, but the total mass remains constant.

Cathode Ray

A stream of electrons observed in vacuum tubes when high voltage is applied; fundamental to early experiments in electricity and atomic structure.

Electrons

Negatively charged subatomic particles discovered by J.J. Thompson, which exist in an atom.

Plum Pudding Model

J.J. Thompson's early model of the atom, where electrons were scattered within a positively charged 'soup'.

Nucleus

The central part of an atom, containing protons and neutrons, which has a positive charge.

Alpha Particles

Positively charged particles emitted from the decay of certain radioactive materials, used in Rutherford's experiments.

Proton

A positively charged subatomic particle found in the nucleus of an atom; discovered by Ernest Rutherford.

Neutron

An uncharged subatomic particle found in the nucleus of an atom, discovered by James Chadwick.

Millikan Oil Drop Experiment

An experiment designed by Robert A. Millikan to measure the charge of the electron by balancing the gravitational and electric forces on charged oil droplets.

Charge to Mass Ratio

The proportional relationship of the charge of a particle to its mass; determined for electrons by J.J. Thompson.

Energy Levels

Specific regions around the nucleus of an atom where electrons are likely to be found, proposed by Niels Bohr.

Quantum Mechanics

The branch of physics that describes the behavior of matter and energy at the atomic and subatomic levels.

Discrete Energy Levels

Specific amounts of energy that an electron must absorb to move between different energy levels.

Gaussian Distribution

A probability distribution often used to describe the distribution of charges on oil droplets in Millikan’s experiment.

Ionization

The process by which an atom or a molecule acquires a positive or negative charge by gaining or losing electrons.

Fundamental Unit of Charge

The smallest unit of electric charge, equal to the charge of a single electron, approximately -1.6 × 10^-19 coulombs.