Nuclear Chemistry and Atomic Models Study Guide

Comprehensive vocabulary flashcards covering atomic notation, types of radioactive decay, fission, fusion, key historical atomic models, and atomic mass calculations.

Half-life

The time required for half of a radioactive sample to decay.

Atomic number

The total number of protons in an atom's nucleus.

Mass number

The total number of protons plus the number of neutrons in an atom.

Number of neutrons

Calculated by subtracting the atomic number from the mass number: $\text{Mass number} - \text{Atomic number}$.

Nuclear notation

A standard notation where the mass number is written on the top and the atomic number is written on the bottom to the left of the chemical symbol (e.g., $^{235}_{92}\text{U}$).

Balancing nuclear equations

The requirement that the total mass numbers and total atomic numbers must be equal on both sides of a nuclear reaction.

U-235 + n -> Ba-141 + Kr-92 + 3n + Energy

Alpha particle

A helium nucleus ($^{4}_{2}\text{He}$) containing $2$ protons and $2$ neutrons.

Alpha decay ($\alpha$)

A type of radioactive decay in which an alpha particle ($^{4}_{2}\text{He}$) is emitted, decreasing the mass number by $4$ and the atomic number by $2$.

Beta minus decay ($\beta^-$)

A decay process where a neutron changes into a proton and releases an electron ($^{0}_{-1}\text{e}$), leaving the mass number unchanged and increasing the atomic number by $1$.

C-14 -> N-14 + e- + antineutrino + Energy

Gamma decay ($\gamma$)

A decay process where an excited nucleus releases excess energy as a gamma ray ($^{0}_{0}\gamma$), leaving both the mass number and the atomic number unchanged.

Positron emission ($\beta^+$)

A decay process where a proton changes into a neutron and releases a positron ($^{0}_{+1}\text{e}$), leaving the mass number unchanged and decreasing the atomic number by $1$.

C-11 -> B-11 + e+ + neutrino + Energy

Electron capture

A process where the nucleus captures an electron and a proton changes into a neutron, leaving the mass number unchanged and decreasing the atomic number by $1$.

K-40 + e- -> Ar-40 + neutrino + Energy

Nuclear fission

A reaction in which a large nucleus splits into smaller nuclei, releasing energy and usually neutrons.

U-235 + n -> Ba-141 + Kr-92 + 3n + Energy

Nuclear fusion

A reaction in which small nuclei combine to form a larger nucleus, releasing energy.

H-2 + H-3 -> He-4 + n + Energy

Chain reaction

A self-sustaining series of reactions where neutrons released during fission cause additional fission reactions.

Atomic mass unit (amu)

A unit used to measure the mass of atoms and subatomic particles, where a proton is approximately $1\,\text{amu}$, a neutron is approximately $1\,\text{amu}$, and an electron is approximately $0.00055\,\text{amu}$.

Average atomic mass

The weighted average of the masses of an element's naturally occurring isotopes, calculated as $\Sigma (\text{isotope mass} \times \text{decimal abundance})$.

Democritus

Greek thinker who proposed that matter is made of tiny particles called atoms.

Aristotle

Greek philosopher who believed matter was continuous and made of four elements. Fire, Air, Water, Earth

John Dalton

Scientist who developed the first modern atomic theory, modeling atoms as solid spheres.

J. J. Thomson

Scientist who discovered the electron and proposed the plum pudding model of the atom. Via cathode ray experiment

Robert Millikan

Scientist who measured the charge of the electron using the oil drop experiment.

Ernest Rutherford

Scientist whose gold foil experiment demonstrated that atoms are mostly empty space with a small, dense, positively charged nucleus.

Niels Bohr

Scientist who proposed the planetary atomic model where electrons occupy specific energy levels around the nucleus.

Erwin Schrödinger

Physicist who developed wave mechanics and the wave equation, contributing to the modern quantum model.

Werner Heisenberg

Physicist who formulated the uncertainty principle, which limits how precisely an electron's position and momentum can be known simultaneously.

James Chadwick

Scientist who discovered the neutron in $1932$.

Electron cloud model

An atomic model that describes regions where electrons are likely to be found rather than fixed paths.