Atomic Structure and Quantum Theory Vocabulary

Vocabulary flashcards covering core concepts of atomic structure, subatomic particles, isotopes, electromagnetic radiation, quantum theory, and periodic table organization.

Atomic Number ($Z$)

The number of protons in the nucleus of an atom, which uniquely identifies a chemical element.

Mass Number ($A$)

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

Isotope

Atoms of the same element that have the same atomic number ($Z$) but different mass numbers ($A$) due to a different number of neutrons.

Cation

A positively charged ion formed when a neutral atom loses electrons, resulting in more protons than electrons (e.g., $\text{Ca}^{2+}$).

Anion

A negatively charged ion formed when a neutral atom gains electrons, resulting in more electrons than protons (e.g., $\text{Cl}^-$).

Electromagnetic Radiation

Any form of radiant energy in the electromagnetic spectrum, characterized by electric and magnetic fields oscillating at right angles to one another.

Speed of Light ($c$)

The constant speed at which all electromagnetic radiation travels in a vacuum, equal to $2.998 \times 10^8\,\text{m/s}$.

Wavelength ($\lambda$)

The distance between corresponding points on adjacent waves, inversely related to frequency by $\lambda = \frac{c}{\nu}$.

Frequency ($\nu$)

The number of wave cycles that pass a given point per second, measured in Hertz ($\text{Hz}$) or cycles/sec.

Fraunhofer Lines

A series of narrow dark absorption lines in the spectrum of sunlight that correspond to the atomic emission spectra of specific elements.

Blackbody Radiators

Sources of radiant energy studied by Kirchhoff that act as perfect absorbers of light when cold and perfect radiators of light when hot.

Quantum

The discrete elementary unit of electromagnetic energy proposed by Max Planck that objects emit or absorb in integral multiples ($E = h\nu$).

Planck Constant ($h$)

A physical constant equal to $6.626 \times 10^{-34}\,\text{J}\cdot\text{s}$ that relates the energy of a photon to its frequency.

Photoelectric Effect

The emission of electrons from a metal surface when illuminated by light with a frequency that exceeds the threshold frequency ($\nu_0$).

Work Function ($\Phi$)

The minimum photon energy required to eject an electron from a metal surface, defined by $\Phi = h\nu_0$.

Cathode Ray Tube Experiment

An experiment conducted by J. J. Thomson in 1897 demonstrating that cathode ray beams deflect toward positively charged plates, proving atoms contain negatively charged electrons.

Millikan's Oil-Drop Experiment

An experiment performed by Robert Millikan in 1909 that measured the charge of an electron as $e = -1.602 \times 10^{-19}\,\text{C}$ and calculated its mass as $m_e = 9.109 \times 10^{-31}\,\text{kg}$.

Plum-Pudding Model

J. J. Thomson's atomic model depicting electrons distributed throughout a diffuse, positively charged sphere.

Beta Particle ($\beta$)

A high-energy, high-speed electron emitted during radioactive decay.

Alpha Particle ($\alpha$)

A positively charged radioactive particle with a $2+$ charge and a mass equivalent to a helium nucleus.

Rutherford's Gold Foil Experiment

An experiment in which alpha particles were directed at thin gold foil, revealing that atoms contain a tiny, dense, positively charged nucleus.

Proton

A positively charged subatomic particle in the nucleus with a relative charge of $1+$ ($+1.60218 \times 10^{-19}\,\text{C}$) and a mass of $1.00728\,\text{u}$ ($1.67262 \times 10^{-27}\,\text{kg}$).

Neutron

An electrically neutral subatomic particle in the nucleus with a relative charge of $0$ and a mass of $1.00866\,\text{u}$ ($1.67493 \times 10^{-27}\,\text{kg}$).

Unified Atomic Mass Unit ($\text{u}$)

A unit of mass equal to exactly $\frac{1}{12}$ of the mass of a carbon-12 atom, also known as a Dalton ($\text{Da}$).

Nuclide

An atomic species defined by its specific nuclear composition, represented by the symbol $^A_Z\text{X}$.

Periods

The 7 horizontal rows of the periodic table, arranged in order of increasing atomic number.

Groups

The 18 vertical columns of the periodic table (also called families) containing elements that exhibit similar chemical and physical properties.

Metals

Elements that are typically shiny solids, malleable, ductile, and good conductors of heat and electricity, with mercury as a liquid exception.

Nonmetals

Elements that are poor conductors of heat and electricity, existing as brittle solids, liquids, or gases.

Metalloids

Elements with intermediate properties between metals and nonmetals, acting as semiconductors and appearing shiny yet brittle.

Alkali Metals

The elements in Group 1 of the periodic table, which form monatomic cations with a $1+$ charge.

Alkaline Earth Metals

The elements in Group 2 of the periodic table, which form monatomic cations with a $2+$ charge.

Chalcogens

The elements in Group 16 of the periodic table, which commonly form monatomic anions with a $2-$ charge.

Halogens

The elements in Group 17 of the periodic table, which commonly form monatomic anions with a $1-$ charge.

Noble Gases

The elements in Group 18 of the periodic table, characterized by their lack of chemical reactivity.