Introduction to Atomic Theory and Subatomic Structure

A set of vocabulary flashcards covering basic atomic theory, historical atomic models, subatomic particles, atomic numbers, isotopes, and atomic mass calculations.

Law of Conservation of Mass

A scientific law stating that mass is conserved during chemical reactions—such as $16\,g$ of oxygen and $2\,g$ of hydrogen combining to form $18\,g$ of water—because the subatomic particles themselves do not change mass.

John Dalton

The scientist often referred to as the father of chemistry who formulated atomic theory to explain why scientific laws like conservation of mass occur.

Scientific Theory

A well-substantiated explanation of observed natural phenomena that explains why things happen, rather than being something merely theoretical.

Scientific Law

A concise statement or observation of a phenomenon that occurs consistently in nature over and over again without providing an explanation as to why it occurs.

Cathode Ray Tube (CRT)

An evacuated glass tube with electrodes that allows the observation and detection of negatively charged subatomic particles transferred across a voltage gap.

Electron

A negatively charged subatomic particle designated as $e^-$ that has a high charge-to-mass ratio and an exceptionally light mass of approximately $10^{-28}\,g$.

Milliken's Oil Drop Experiment

An experiment that used ionized oil droplets, X-rays, and electric fields to determine the electrical charge and mass of an individual electron.

Plum Pudding Theory

An early atomic model proposing that an atom consists of a continuous positive background sphere (pudding) with negatively charged electrons (raisins) embedded throughout.

Rutherford's Gold Foil Experiment

An experiment that bombarded gold foil with alpha particles, revealing that atoms are mostly empty space with almost all mass concentrated in a tiny central nucleus.

Proton

A positively charged subatomic particle located in the center of the atom, designated by the symbol $p$.

Neutron

A neutral subatomic particle located in the nucleus of an atom that adds mass nearly identical to that of a proton without adding electrical charge.

Atomic Number ($Z$)

The total number of protons in an atom's nucleus, represented by the capital letter $Z$, which uniquely defines the identity of an element.

Mass Number ($A$)

The total sum of the number of protons and neutrons in the nucleus of an atom, designated by the capital letter $A$.

Isotopes

Atoms of the same element that contain the same number of protons but different numbers of neutrons, resulting in different mass numbers.

Atomic Mass Unit (AMU)

A relative mass unit defined exactly as $\frac{1}{12}$ of the mass of a carbon-12 atom, where one carbon-12 atom is set to exactly $12\,\text{AMU}$.

Deuterium

An isotope of hydrogen containing one proton and one neutron, giving it an atomic mass of approximately $2.014\,\text{AMU}$.

Weighted Average Atomic Mass

The average atomic mass of an element calculated by multiplying the mass of each naturally occurring isotope by its fractional natural abundance and summing the results.