Atoms modeled by quantum mechanics

quantized

having values restricted to whole-number multiples of a specific base value;

photon

a quantum of electromagnetic radiation;

quantum theory

a model based on the idea that energy is absorbed and emitted in discrete quantities of energy called quanta;

photoelectric effect

the phenomenon of light striking a metal surface and producing an electric current (a flow of electrons);

threshold frequency (ν₀)

the minimum frequency of light required to produce the photoelectric effect;

work function (Φ)

the amount of energy needed to remove an electron from the surface of a metal;

wave–particle duality

the behavior of an object that exhibits the properties of both a wave and a particle;

ground state

the most stable, lowest-energy state available to an atom, ion, or molecule;

excited state

any energy state above the ground state in an atom, ion, or molecule;

electron transition

the movement of an electron between energy levels;

standing wave

a wave confined to a given space, with a wavelength (λ) related to the length L of the space by L = n(λ/2), where n is a whole number;

node

a location in a standing wave that experiences no displacement; in the context of orbitals, nodes are locations at which electron density goes to zero;

Heisenberg uncertainty principle

the principle that we cannot determine both the position and the momentum of a particle in an atom at the same time;

wave mechanics (also called quantum mechanics)

a mathematical description of the wavelike behavior of particles on the atomic level;

Schrödinger wave equation

a description of how the electron matter wave varies with location and time around the nucleus of a hydrogen atom;

wave function (ψ)

a solution to the Schrödinger wave equation;

orbital

a region around the nucleus of an atom where the probability of finding an electron is high; each orbital is defined by the square of the wave function (ψ²) and is identified by a unique combination of three quantum numbers;

quantum number

a number that specifies the energy, the probable location or orientation of an orbital, or the spin of an electron within an orbital;

principal quantum number (n)

a positive integer describing the relative size and energy of an atomic orbital or group of orbitals in an atom;

angular momentum quantum number (ℓ)

an integer having any value from 0 to n − 1 that defines the shape of an orbital;

magnetic quantum number (mₗ)

an integer that may have any value from −ℓ to +ℓ, where ℓ is the angular momentum quantum number; it defines the orientation of an orbital in space;

spin magnetic quantum number (mₛ)

either +½ or −½, indicating that the spin orientation of an electron is either up or down, respectively;

Pauli exclusion principle

the principle that no two electrons in an atom can have the same set of four quantum numbers;

aufbau principle

the method of building electron configurations of atoms by adding one electron at a time as atomic number increases across the rows of the periodic table; each electron goes into the lowest-energy orbital available;

electron configuration

the distribution of electrons among the orbitals of an atom or ion;

orbital diagram

depiction of the arrangement of electrons in an atom or ion, using boxes to represent orbitals;

effective nuclear charge (Zₑff)

the attraction toward the nucleus experienced by a valence-shell electron, which is approximately equal to the sum of the positive charge on the nucleus and the total negative charge of all inner-shell electrons;