Unit 2: Atomic Structure, the Mole, and Nuclear Chemistry

Vocabulary practice flashcards covering atomic theory development, subatomic particles, isotopes, mole calculations, and radioactive decay processes.

Democritus

Greek philosopher (c. 400 B.C.) who was the first person to propose that nature's basic particle is an indivisible unit called the atom.

Aristotle

Ancient Greek philosopher who rejected the idea of atoms, proposing instead that matter is continuous and composed of four elements: earth, air, fire, or water.

Law of Conservation of Matter

A fundamental chemical law formulated by Antoine Lavoisier in the 1700s stating that matter cannot be created or destroyed in chemical reactions.

Dalton's Atomic Theory

Theory proposed in 1808 stating that all matter consists of indivisible atoms, atoms of a given element are identical, atoms combine in whole-number ratios to form compounds, and chemical reactions rearrange atoms.

Cathode Ray Tube (CRT)

An evacuated glass tube used in electrical experiments where deflection of beams by electric and magnetic fields led to the discovery of electrons.

J. J. Thomson

Physicist who discovered electrons in 1897 using cathode ray tubes, showed their charge-to-mass ratio is constant, and won the 1906 Nobel Prize in Physics.

Robert Millikan

Physicist who conducted experiments determining that every electron possesses the exact same negative charge, winning the 1923 Nobel Prize in Physics.

Plum-Pudding Model

An atomic model proposed by J. J. Thomson in which tiny negatively charged electrons are embedded throughout a uniform, positively charged sphere containing most of the atom's mass.

Rutherford's Gold Foil Experiment

A 1910 experiment by Ernest Rutherford, Hans Geiger, and Ernest Marsden firing alpha particles at thin gold foil, revealing that atoms have a dense, positively charged nucleus.

Proton

A positively charged subatomic particle discovered by Rutherford (1914–1917) located in the nucleus with a relative charge of $+1$ and a mass $1840$ times that of an electron.

Neutron

A neutral subatomic particle in the atomic nucleus discovered in 1932 by James Chadwick, having a relative mass of $1$ and a charge of $0$.

Electron

A negatively charged subatomic particle located outside the nucleus with a relative charge of $-1$ and a relative mass of $\frac{1}{1840}$.

Atomic Number ($Z$)

The number of protons in an atom's nucleus, which uniquely defines the element and equals the number of electrons in a neutral atom.

Mass Number ($A$)

The total count of protons plus neutrons in an individual atom's nucleus; it does not appear on the periodic table.

Hyphen Notation

A method of specifying an isotope by writing the full name of the element, a hyphen, and its mass number (e.g., cobalt-60 or platinum-195).

Nuclear Symbol Notation

A symbol notation showing an element's symbol preceded by its mass number as a superscript and atomic number as a subscript (e.g., $^{195}_{78}\text{Pt}$).

Isotopes

Atoms of the same element containing identical proton counts (atomic numbers) but different neutron counts (mass numbers).

Atomic Mass Unit (amu)

A mass unit defined as exactly $\frac{1}{12}$ the mass of a carbon-12 atom, roughly equivalent to the mass of one proton or neutron.

Average Atomic Mass

The weighted average mass of all naturally occurring isotopes of an element, calculated using each isotope's atomic mass and relative abundance.

Mole

The SI unit for amount of substance, defined as the amount containing as many representative particles as there are atoms in exactly $12\,\text{g}$ of carbon-12.

Avogadro's Number

The number of representative particles contained in exactly one mole of any substance, equal to $6.022 \times 10^{23}\,\text{particles/mol}$.

Molar Mass

The mass in grams of one mole of a pure substance, numerically equivalent to its atomic or formula mass from the periodic table.

Mole Highway

A quantitative conversion framework linking number of particles, moles, and mass in grams using Avogadro's number and molar mass.

Radioactive Decay

The spontaneous disintegration of an unstable atomic nucleus accompanied by the release of particles, electromagnetic radiation, or both.

Transmutation

The conversion of an atom of one element into an atom of a different element, occurring specifically through a change in proton number.

Nucleon

A general term for any subatomic particle located within the atomic nucleus (protons and neutrons).

Nuclide

A term for a specific atom characterized by the exact composition of its nucleus (number of protons and neutrons).

Alpha ($\alpha$) Radiation

A form of radioactive decay emitting a helium nucleus ($^{4}_{2}\text{He}^{2+}$), decreasing atomic number by $2$ and mass number by $4$; can be blocked by paper.

Beta ($\beta$) Radiation

Nuclear decay emitting a high-speed electron ($^{0}_{-1}e$) when a neutron decays into a proton; increases atomic number by $1$; blocked by lead or glass.

Gamma ($\gamma$) Radiation

High-energy electromagnetic radiation emitted alongside alpha or beta decay that carries neither mass nor electrical charge.

Positron Emission

A radioactive decay process emitting a positron ($^{0}_{+1}e$), a particle with the mass of an electron but positive charge, decreasing atomic number by $1$.

Electron Capture

A nuclear reaction in which an inner electron is absorbed by the nucleus and combines with a proton to form a neutron, decreasing atomic number by $1$.