3.9: Key Terms

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actinide: inner transition metal in the bottom of the bottom two rows of the periodic table

alkali metal: element in group 1

alkaline earth metal: element in group 2

amplitude: extent of the displacement caused by a wave

atomic orbital: mathematical function that describes the behavior of an electron in an atom (also called the wavefunction)

Aufbau principle: 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

blackbody: idealized perfect absorber of all incident electromagnetic radiation; such bodies emit electromagnetic radiation in characteristic continuous spectra called blackbody radiation

Bohr’s model of the hydrogen atom: structural model in which an electron moves around the nucleus only in circular orbits, each with a specific allowed radius

chalcogen: element in group 16

continuous spectrum: electromagnetic radiation given off in an unbroken series of wavelengths (e.g., white light from the sun)

core electron: electron in an atom that occupies the orbitals of the inner shells

covalent bond: attractive force between the nuclei of a molecule’s atoms and pairs of electrons between the atoms

covalent compound: (also, molecular compound) composed of molecules formed by atoms of two or more different elements

covalent radius: one-half the distance between the nuclei of two identical atoms when they are joined by a covalent bond

d orbital: region of space with high electron density that is either four lobed or contains a dumbbell and torus shape; describes orbitals with l = 2.

degenerate orbitals: orbitals that have the same energy

effective nuclear charge: charge that leads to the Coulomb force exerted by the nucleus on an electron, calculated as the nuclear charge minus shielding

electromagnetic radiation: energy transmitted by waves that have an electric-field component and a magnetic-field component

electromagnetic spectrum: range of energies that electromagnetic radiation can comprise, including radio, microwaves, infrared, visible, ultraviolet, X-rays, and gamma rays

electron affinity: energy change associated with addition of an electron to a gaseous atom or ion

electron configuration: listing that identifies the electron occupancy of an atom’s shells and subshells

electron density: 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

endothermic: processes that increase the energy of an atom and involve the absorption of light

excited state: state having an energy greater than the ground-state energy

exothermic: processes that decrease the energy of an atom and involve the emission of light

f orbital: multilobed region of space with high electron density, describes orbitals with l = 3

frequency (ν): number of wave cycles (peaks or troughs) that pass a specified point in space per unit time

ground state: state in which the electrons in an atom, ion, or molecule have the lowest energy possible

group: vertical column of the periodic table

halogen: element in group 17

Heisenberg uncertainty principle: 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

hertz (Hz): the unit of frequency, which is the number of cycles per second, s⁻¹

Hund’s rule: 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

inert gas: (also, noble gas) element in group 18

inner transition metal: (also, lanthanide or actinide) element in the bottom two rows; if in the first row, also called lanthanide, or if in the second row, also called actinide

intensity: property of wave-propagated energy related to the amplitude of the wave, such as brightness of light or loudness of sound

interference pattern: pattern typically consisting of alternating bright and dark fringes; it results from constructive and destructive interference of waves

ionic bond: electrostatic forces of attraction between the oppositely charged ions of an ionic compound

ionic compound: compound composed of cations and anions combined in ratios, yielding an electrically neutral substance

ionization energy: energy required to remove an electron from a gaseous atom or ion

isoelectronic: group of ions or atoms that have identical electron configurations

lanthanide: inner transition metal in the top of the bottom two rows of the periodic table

line spectrum: electromagnetic radiation emitted at discrete wavelengths by a specific atom (or atoms) in an excited state

magnetic quantum number (m_l): quantum number signifying the orientation of an atomic orbital around the nucleus

main-group element: (also, representative element) element in groups 1, 2, and 13–18

metal: element that is shiny, malleable, good conductor of heat and electricity

metalloid: element that conducts heat and electricity moderately well, and possesses some properties of metals and some properties of nonmetals

molecular compound: (also, covalent compound) composed of molecules formed by atoms of two or more different elements

monatomic ion: ion composed of a single atom

noble gas: (also, inert gas) element in group 18

node: any point of a standing wave with zero amplitude

nonmetal: element that appears dull, poor conductor of heat and electricity

orbital diagram: pictorial representation of the electron configuration showing each orbital as a box and each electron as an arrow

oxyanion: polyatomic anion composed of a central atom bonded to oxygen atoms

p orbital: dumbbell-shaped region of space with high electron density, describes orbitals with l = 1

Pauli exclusion principle: specifies that no two electrons in an atom can have the same value for all four quantum numbers

period: (also, series) horizontal row of the periodic table

periodic law: properties of the elements are periodic function of their atomic numbers

periodic table: table of the elements that places elements with similar chemical properties close together

photon: smallest possible packet of electromagnetic radiation, a particle of light

pnictogen: element in group 15

polyatomic ion: ion composed of more than one atom

principal quantum number (n): quantum number specifying the shell an electron occupies in an atom

quantization: limitation of some property to specific discrete values, not continuous

quantum mechanics: field of study that includes quantization of energy, wave-particle duality, and the Heisenberg uncertainty principle to describe matter

quantum number: number having only specific allowed values and used to characterize the arrangement of electrons in an atom

representative element: (also, main-group element) element in columns 1, 2, and 12–18

s orbital: spherical region of space with high electron density, describes orbitals with l = 0

secondary (angular momentum) quantum number (l): quantum number distinguishing the different shapes of orbitals; it is also a measure of the orbital angular momentum

series: (also, period) horizontal row of the period table

shell: atomic orbitals with the same principal quantum number, n

spin quantum number (m_s): number specifying the electron spin direction, either $+ \frac{1}{2}$ or $- \frac{1}{2}$

standing wave: (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

subshell: atomic orbitals with the same values of n and l

transition metal: element in groups 3–12 (more strictly defined, 3–11; see chapter on transition metals and coordination chemistry)

valence electrons: electrons in the high energy outer shell(s) of an atom

valence shell: high energy outer shell(s) of an atom

wave: oscillation of a property over time or space; can transport energy from one point to another

wave-particle duality: observation that elementary particles can exhibit both wave-like and particle-like properties

wavefunction (ψ): 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

wavelength (λ): distance between two consecutive peaks or troughs in a wave

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