Chapter 1/2 vocabulary terms

antibonding MO

atomic number

The number of protons in the nucleus of an atom

Aufbau principle

The rules for determining the electron configuration of an atom

Bond angle

The angle formed between two adjacent bonds

Bond length

The equilibrium distance between the nuclei of two atoms that are bonded to eachother

bond strength

The amount of energy needed to break a bond and produce two radical fragments

bonding MO

A molecular orbital that is lower in energy than the atomic orbitals from which it is formed

condensed structure

A shorthand way of writing structures in which carbon-hydrogen and carbon-carbon bonds are understood rather than shown explicitly

covalent bond

A bond formed by sharing electrons between atoms

electron shell

A group of an atom’s electrons with the same principal quantum number

electron-dot structure

A representation of a molecule showing valence electrons as dots

ground-state electron configuration

The most stable, lowest-energy electron configuration of a molecule or atom

Hund’s rule

If two or more empty orbitals of equal energy are available, one electron occupies each, with their spins parallel, until all are half-full

ionic bond

The electrostatic attraction between ions of unlike charge

isotope

Atoms of the same element that have different mass numbers

Kekule structure

An alternative name for a line-bond structure, which represents a molecules by showing covalent bonds as lines between atoms

Lewis structure

Representations of molecules showing valence electrons as dots

line-bond structure

An alternative name for a Kekule structure, which represents a molecule by showing covalent bonds as lines between atoms

lone-pair electrons

Nonbonding valence-shell electron pairs. Lone-pair electrons are used by nucleophiles in their reactions with electrophiles

molecular orbital (MO) theory

A description of covalent bond formation as resulting from a mathematical combination of atomic orbitals (wave functions) to form molecular orbitals

molecule

A neutral collection of atoms held together by covalent bonds

node

A surface of zero electron density within an orbital

nonbonding electron

Valence electrons that are not used in forming covalent bonds

orbital

A wave function, which describes the volume of space around a nucleus in which an electron is most likely to be found

Pauli exclusion principle

No more than two electrons can occupy the same orbital, and those two must have spins of opposite sign

pi bond

The covalent bond formed by sideways overlap of atomic orbitals

sigma bond

A covalent bond formed by head-on overlap of atomic orbitals

skeletal structure

A shorthand way of writing structures in which carbon atoms are assumed to be at each intersection of two lines (bonds) and at the end of each line

sp hybrid orbital

Hybrid orbitals derived from the combination of an s and a p atomic orbital. The two resulting orbitals from hybridization are oriented at an angle of 180^o to each other

sp² hybrid orbital

Hybrid orbitals derived by combination of an s atomic orbital with two p atomic orbitals. The three hybrid orbitals that result lie in a plane at angles of 120^o to each other 

sp³ hybrid orbital

Hybrid orbitals derived by combination of an s atomic orbital with three p atomic orbitals. The four hybrid orbitals that result are directed toward the corners of a regular tetrahedron at angles of 109^o to each other

valence bond (VB) theory

A bonding theory that describes a covalent bond as resulting from the overlap of two atomic orbitals

valence shell

The outermost electron shell of an atom

acidity constant (K_a)

A measure of acid strength

alkaloid

Naturally occurring organic bases

Bronsted-Lowry acid

A substance that donates a hydrogen ion to a base

Bronsted-Lowry base

A substance that accepts H⁺ from an acid

conjugate acid

The product that results from protonation of a Bronsted-Lowry base

conjugate base

The product that results from deprontonation of a Bronsted-Lowry acid

dipole moment

A measurfe of the net polarity of a molecule, it arises when the centers of mass of positive and negative charges within a molecule do not coincide

dispersion force

Non-covalent interactions between molecules that arise because of constantly changing electron distributions within the molecules

electronegativity (EN)

The ability of an atom to attract electrons in a covalent bond

electrostatic potential map

Molecular representations that use color to indicate the charge distribution in the molecules as derived from quantum-mechanical calculations

formal charge

The difference in the number of electrons owned by an atom in a molecule and by the same atom in its elemental state

hydrogen bond

A weak attraction between a hydrogen atom bonded to an electronegative atom and an electron lone pair on another electronegative atom

hydrophilic

water-loving; attracted to water

hydrophobic

Water-fearing; repelled by water

inductive effect

The electron-attracting or electron-withdrawing effect transmitted through sigma bonds.

intermolecular force

A reaction that occurs between two molecules

Lewis acid

A substance with a vacant low-energy orbital that can accept an electron pair from a base

Lewis base

A substance that donates an electron lone pair to an acid

noncovalent interaction

One of a variety of nonbonding interactions between molecules, such as dipole-dipole forces, dispersion forces, and hydrogen bonds

pK_a

The negative common logarithm of the K_a; used to express acid strength

polar covalent bond

A covalent bond in which the electron distribution between atoms is unsymmetrical

resonance form

Individual structural forms of a resonance hybrid

resonance hybrid

A molecule that can’t be represented adequately by a single Kekule structure but must instead be considered as an average of two or more forms. The forms themselves differ only in the positions of their electrons, not their nuclei.

van der Waals force

Intermolecular forces that are responsible for holding molecules together in the liquid and solid states