# Electron Behavior and Periodic Properties of Elements

## Vocabulary

### amplitude

height of a wave, measured as the distance from the point of equilibrium to a crest or a trough

### Aufbau principle

principle that states that electrons fill orbitals in order of increasing energy

### de Broglie hypothesis

idea that matter may behave as a wave

### de Broglie wavelength

wavelength ($\lambda$) of a particle having mass m and traveling at velocity v using Planck's constant, h; given as $\lambda=\frac h{mv}$

### degenerate orbital

one of two or more orbitals with the same energy

wave of energy produced by the movement of particles through space

### electromagnetic spectrum

entire range of electromagnetic waves, defined by their energy, wavelengths, and frequencies

### electron configuration

orbital filling of electrons in an atom based on their quantum numbers in increasing energies

### electron orbital

area of an atom in which an electron has the greatest probability of being located. Each orbital can contain at most two electrons.

### electron shell

one or more electron subshells that have the same quantum number $n$

### electron subshell

group of electron energy levels with the same size and shape that have the same quantum numbers $n$ and $\ell$

### excited state

electron state that has a higher energy level than the lowest energy state (ground state)

### frequency

number of oscillations of a wave that occur in a given period of time, usually a second, measured in hertz (Hz)

### ground state

electron state that is lowest in energy

### Heisenberg uncertainty principle

principle that it is impossible to simultaneously measure the position and the momentum of a particle

### Hund's rule

rule that states that when filling degenerate orbitals (for example, the 3p orbital), electrons must first singly occupy all the empty orbitals in the subshell before pairing within the same orbital

### line spectrum

pattern of colors on a dark background produced by an element when it gives off light (emission) or a pattern of dark lines on a background of the electromagnetic spectrum produced by an element when it absorbs light (absorption)

### node

point on a standing wave that stays fixed and does not oscillate

### Pauli exclusion principle

principle that states that paired electrons may never have the same spin value, which means they cannot have the same four quantum numbers

### photoelectric effect

emission of electrons when light strikes a material

### photon

fundamental particle that has a fixed amount of energy stored as electromagnetic radiation

### Planck's constant (h)

$6.62607\times 10^{-34}\;\rm{J}\cdot\rm{s}$; describes the ratio of energy to frequency of a photon

### quantized

exists only as discrete values

### quantum mechanics

branch of science that deals with subatomic particles, their behaviors, and their interactions

### quantum number

one of four numbers, $n$, $\ell$, $m$, and $s$, that together describe the orbital state of subatomic electrons

### wave

periodic oscillation of energy or matter

### wave function

mathematical expression that gives information about measurable properties of a system, such as energy, momentum, and position

### wave-particle duality

having properties of both particles and waves

### wavelength

distance between two identical parts of a wave