# Chapter 5 Vocabulary

Energy level

The specific energies an electron in an atom or other system can have.

Quantum

The amount of energy needed to move an electron from one energy level to another.

Quantum mechanical model

The modern description, primarily mathematical, of the behavior of electrons in atoms.

Atomic orbital

A mathematical expression describing the probability of finding an electron at various locations; usually represented by the region of space around the nucleus where there is a high probability of finding an electron.

Electron configuration

The arrangement of electrons of an atom in its ground state into various orbitals around the nuclei of atoms.

Aufbau principle

The rule that electrons occupy the orbitals of the lowest energy first

Paul's explosion principle

An atomic orbital may describe at most two electrons, each with opposite spin direction.

Spin

A quantum mechanical property of electrons that may be thought of as clockwise or counterclockwise.

Hund's rule

Electrons occupy orbitals of the same energy in a way that makes the number or electrons with the same spin directions as large as possible.

Amplitude

The height of a wave's crest.

Wavelength

The distance between adjacent crests of a waves.

Frequency

The number of wave cycles that pass a given point per unit of time; frequency and wavelength are inversely proportional to each other.

Hertz (Hz)

The unit of frequency, equal the one cycle per second.

Energy waves that travel in a vacuum at a speed of 2.998 X 10^8 m/s; includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays.

Spectrum

Wavelengths of visible light that are separated when a beam of light passes through a prism; range of wavelengths of eletromagnetic radiation.

Atomic emission spectrum

The pattern formed when light passes through a prism or diffraction grating to separated it into the different frequencies of light it contains.

Planck's constant (h)

A number used to calculate the radiant energy (E) absorbed or emitted by a body based on the frequency of radiation.

Photoelectric effect

The ejection of electrons by certain metals when they absorb light with a frequency above a threshold frequency.

Photon

A quantum of light; a discrete bundle of electromagnetic energy that interacts with matter similarly to particles.

Ground state

The lowest possible energy of an atoms described by quantum mechanics.

Heisenberg uncertainty principle

It is possible to know exactly both the velocity and the position of a particle at the same time.