Chemical Bonds (chapter 8)

ionic bond

a chemical bond that results from the electrostatic attraction between a cation and an anion;

bond length

the distance between the nuclear centers of two atoms joined in a bond;

metallic bond

a chemical bond consisting of metal atoms sharing a “sea” of electrons;

delocalized electrons

electrons that are shared among more than two atoms;

octet rule

the tendency of atoms of main group elements to make bonds by gaining, losing, or sharing electrons to achieve a valence shell containing eight electrons (i.e., four electron pairs);

Lewis symbol

(also called Lewis dot symbol) a system in which the chemical symbol for an element is surrounded by one or more dots representing each of its atom’s valence electrons;

bonding capacity

the number of covalent bonds an atom forms to have an octet of electrons in its valence shell;

Lewis structure

a two-dimensional representation of the bonds and lone pairs of valence electrons in a molecule or polyatomic ion;

bonding pair

a pair of electrons shared between two atoms;

single bond

a chemical bond that results when two atoms share one pair of electrons;

lone pair

a pair of valence electrons that is not shared;

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

aldehyde

an organic compound having a carbonyl group with a single bond to a hydrogen atom and a single bond to another atom or group of atoms, designated as R– in the general formula RCHO.

carbonyl group

a carbon atom with a double bond to an oxygen atom.

polar covalent bond

a bond characterized by unequal sharing of bonding pairs of electrons between atoms.

bond polarity

a measure of the extent to which bonding electrons are unequally shared.

electronegativity

a relative measure of the ability of an atom to attract electrons in a bond to itself.

allotropes

different molecular forms of an element.

resonance

a characteristic of electron distributions when two or more equivalent Lewis structures can be drawn for one compound.

resonance structure

one of two or more Lewis structures with the same arrangement of atoms but different arrangements of bonding pairs of electrons.

double bond

a chemical bond in which two atoms share two pairs of electrons

triple bond

a chemical bond in which two atoms share three pairs of electrons

formal charge (FC)

a value calculated for an atom in a molecule or polyatomic ion by determining the difference between the number of valence electrons in the free atom and the sum of lone-pair electrons plus half of the electrons in the atom’s bonding pairs

free radical

an odd-electron molecule with an unpaired electron in its Lewis structure

Ionic character

an estimate of the magnitude of charge separation in a covalent bond