Light, energy levels and electron shells. Discover the words that explain how electrons are arranged and why the periodic table looks the way it does.
These terms were extracted from Chemistry by OpenStax, eCampusOntario (© 2016 Rice University; adapted by BCcampus) which is licensed under a Creative Commons Attribution 4.0 International License.
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extent of the displacement caused by a wave (for sinusoidal waves, it is one-half the difference from the peak height to the trough depth, and the intensity is proportional to the square of the amplitude)
The amplitude corresponds to the magnitude of the wave’s displacement and so, in Figure 1, this corresponds to one-half the height between the peaks and troughs.
idealized perfect absorber of all incident electromagnetic radiation; such bodies emit electromagnetic radiation in characteristic continuous spectra called blackbody radiation
A blackbody is a convenient, ideal emitter that approximates the behavior of many materials when heated.
electromagnetic radiation given off in an unbroken series of wavelengths (e.g., white light from the sun)
Such lighting consists of a range of broadly distributed frequencies that form a continuous spectrum.
energy transmitted by waves that have an electric-field component and a magnetic-field component
It emits not only visible light but also infrared light, X-rays, and other forms of electromagnetic radiation.
range of energies that electromagnetic radiation can comprise, including radio, microwaves, infrared, visible, ultraviolet, X-rays, and gamma rays; since electromagnetic radiation energy is proportional to the frequency and inversely proportional to the wavelength, the spectrum can also be specified by ranges of frequencies or wavelengths
Many valuable technologies operate in the radio (3 kHz-300 GHz) frequency region of the electromagnetic spectrum.
number of wave cycles (peaks or troughs) that pass a specified point in space per unit time
The frequency is the number of wave cycles that pass a specified point in space in a specified amount of time (in the SI system, this is measured in seconds).
the unit of frequency, which is the number of cycles per second, s⁻¹
The unit for frequency, expressed as cycles per second [s⁻¹], is the hertz (Hz).
property of wave-propagated energy related to the amplitude of the wave, such as brightness of light or loudness of sound
The amplitude is related to the intensity of the wave, which for light is the brightness, and for sound is the loudness.
pattern typically consisting of alternating bright and dark fringes; it results from constructive and destructive interference of waves
Figure 5 shows the interference patterns that arise when light passes through narrow slits closely spaced about a wavelength apart.
electromagnetic radiation emitted at discrete wavelengths by a specific atom (or atoms) in an excited state
Passing the light through a prism produces a line spectrum, indicating that this light is composed of photons of four visible wavelengths, as shown in Figure 12.
any point of a standing wave with zero amplitude
Since the number of nodes is n – 1, the energy can also be said to depend on the number of nodes, generally increasing as the number of nodes increases.
smallest possible packet of electromagnetic radiation, a particle of light
Electrons were ejected when hit by photons having sufficient energy (a frequency greater than the threshold).
occurring only in specific discrete values, not continuous
This is an example of quantization, in which only discrete values from a more general set of continuous values of some property are observed.
(also, stationary wave) localized wave phenomenon characterized by discrete wavelengths determined by the boundary conditions used to generate the waves; standing waves are inherently quantized
Standing waves (also known as stationary waves) remain constrained within some region of space.
oscillation that can transport energy from one point to another in space
A wave is an oscillation or periodic movement that can transport energy from one point in space to another.
distance between two consecutive peaks or troughs in a wave
As can be seen in Figure 1, the wavelength is the distance between two consecutive peaks or troughs in a wave (measured in meters in the SI system).
term used to describe the fact that elementary particles including matter exhibit properties of both particles (including localized position, momentum) and waves (including nonlocalization, wavelength, frequency)
This is known as wave-particle duality.
structural model in which an electron moves around the nucleus only in circular orbits, each with a specific allowed radius; the orbiting electron does not normally emit electromagnetic radiation, but does so when changing from one orbit to another.
Bohr’s model of the hydrogen atom provides insight into the behavior of matter at the microscopic level, but it is does not account for electron–electron interactions in atoms with more than one electron.
state having an energy greater than the ground-state energy
When an electron transitions from an excited state (higher energy orbit) to a less excited state, or ground state, the difference in energy is emitted as a photon.
state in which the electrons in an atom, ion, or molecule have the lowest energy possible
When the electron is in this lowest energy orbit, the atom is said to be in its ground electronic state (or simply ground state).
integer number having only specific allowed values and used to characterize the arrangement of electrons in an atom
This number, n, is referred to as the principle quantum number.
quantum number distinguishing the different shapes of orbitals; it is also a measure of the orbital angular momentum
Another quantum number is l, the angular momentum quantum number.
mathematical function that describes the behavior of an electron in an atom (also called the wavefunction), it can be used to find the probability of locating an electron in a specific region around the nucleus, as well as other dynamical variables
An atomic orbital, which is distinct from an orbit, is a general region in an atom within which an electron is most probable to reside.
region of space with high electron density that is either four lobed or contains a dumbbell and torus shape; describes orbitals with l = 2. An electron in this orbital is called a d electron
The orbitals with l = 2 are called the d orbitals, followed by the f-, g-, and h-orbitals for l = 3, 4, 5, and there are higher values we will not consider.
a measure of the probability of locating an electron in a particular region of space, it is equal to the squared absolute value of the wave function ψ
The s subshell electron density distribution is spherical and the p subshell has a dumbbell shape.
multilobed region of space with high electron density, describes orbitals with l = 3. An electron in this orbital is called an f electron
The ml degeneracy is the number of orbitals within an l subshell, and so is 2l + 1 (there is one s orbital, three p orbitals, five d orbitals, seven f orbitals, and so forth).
rule stating that it is impossible to exactly determine both certain conjugate dynamical properties such as the momentum and the position of a particle at the same time. The uncertainty principle is a consequence of quantum particles exhibiting wave–particle duality
This is summed up in what we now call the Heisenberg uncertainty principle: It is fundamentally impossible to determine simultaneously and exactly both the momentum and the position of a particle.
quantum number signifying the orientation of an atomic orbital around the nucleus; orbitals having different values of ml but the same subshell value of l have the same energy (are degenerate), but this degeneracy can be removed by application of an external magnetic field
The magnetic quantum number, called ml, specifies the z component of the angular momentum for a particular orbital.
dumbbell-shaped region of space with high electron density, describes orbitals with l = 1. An electron in this orbital is called a p electron
For a given n, p orbitals constitute a p subshell (e.g., 3p if n = 3).
specifies that no two electrons in an atom can have the same value for all four quantum numbers
The Pauli exclusion principle can be formulated as follows: No two electrons in the same atom can have exactly the same set of all the four quantum numbers.
quantum number specifying the shell an electron occupies in an atom
Another name for the principal quantum number is the shell number.
field of study that includes quantization of energy, wave-particle duality, and the Heisenberg uncertainty principle to describe matter
In the realm of quantum mechanics, measurements introduce changes into the system that is being observed.
spherical region of space with high electron density, describes orbitals with l = 0. An electron in this orbital is called an s electron
Orbitals with l = 0 are called s orbitals (or the s subshells).
set of orbitals with the same principal quantum number, n
Another name for the principal quantum number is the shell number.
number specifying the electron spin direction, either +½ or −½
Any electron, regardless of the atomic orbital it is located in, can only have one of those two values of the spin quantum number.
set of orbitals in an atom with the same values of n and l
Orbitals with the same value of l form a subshell.
mathematical description of an atomic orbital that describes the shape of the orbital; it can be used to calculate the probability of finding the electron at any given location in the orbital, as well as dynamical variables such as the energy and the angular momentum
The square of the magnitude of a wavefunction describes the probability of the quantum particle being present near a certain location in space.
procedure in which the electron configuration of the elements is determined by “building” them in order of atomic numbers, adding one proton to the nucleus and one electron to the proper subshell at a time
This procedure is called the Aufbau principle, from the German word Aufbau (“to build up”).
electron in an atom that occupies the orbitals of the inner shells
The electrons occupying the outermost shell orbital(s) (highest value of n) are called valence electrons, and those occupying the inner shell orbitals are called core electrons (Figure 5).
electronic structure of an atom in its ground state given as a listing of the orbitals occupied by the electrons
The arrangement of electrons in the orbitals of an atom is called the electron configuration of the atom.
every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin
Nitrogen (atomic number 7) fills the 1s and 2s subshells and has one electron in each of the three 2p orbitals, in accordance with Hund’s rule.
pictorial representation of the electron configuration showing each orbital as a box and each electron as an arrow
We will now construct the ground-state electron configuration and orbital diagram for a selection of atoms in the first and second periods of the periodic table.
electrons in the outermost or valence shell (highest value of n) of a ground-state atom; determine how an element reacts
The electrons occupying the outermost shell orbital(s) (highest value of n) are called valence electrons, and those occupying the inner shell orbitals are called core electrons (Figure 5).
outermost shell of electrons in a ground-state atom; for main group elements, the orbitals with the highest n level (s and p subshells) are in the valence shell, while for transition metals, the highest energy s and d subshells make up the valence shell and for inner transition elements, the highest s, d, and f subshells are included
Hence, potassium corresponds to Li and Na in its valence shell configuration.
one-half the distance between the nuclei of two identical atoms when they are joined by a covalent bond
Consequently, the size of the atom (and its covalent radius) must increase as we increase the distance of the outermost electrons from the nucleus.
charge that leads to the Coulomb force exerted by the nucleus on an electron, calculated as the nuclear charge minus shielding
This can be explained with the concept of effective nuclear charge, Zeff.
energy required to add an electron to a gaseous atom to form an anion
The electron affinity [EA] is the energy change for the process of adding an electron to a gaseous atom to form an anion (negative ion).
energy required to remove an electron from a gaseous atom or ion. The associated number (e.g., second ionization energy) corresponds to the charge of the ion produced (X²⁺)
Thus, for hydrogen in the ground state n = 1, the ionization energy would be:
group of ions or atoms that have identical electron configurations
Atoms and ions that have the same electron configuration are said to be isoelectronic.