CHEM 257: Exam 1 Terms

Taught by Dr. McGill @ Texas A&M University

Condensed structure

Written formula where carbon-carbon and carbon-hydrogen bonds aren’t shown, just assumed

Covalent bond

A bond that is formed when an electron pair is shared between atoms

Lewis-dot structure

Structure in which the valence-shell electrons of an atom are represented as dots

Electron configuration

The arrangement of an atom’s electrons in specific atomic orbitals around the nucleus

Ionic bond

A bond that forms when atoms transfer electrons, or a bond between a metal and a nonmetal

Kekulé structure

Structure in which two-electron covalent bonds are indicated as lines drawn between atoms

Lone-pair electrons (aka nonbonding electrons)

Valence electrons that are not used for bonding remain as dots in structures

Molecular orbital (MO) theory

Theory that describes covalent bond formation as arising from a mathematical combination of atomic orbitals (wave functions) on different atoms to form molecular orbitals

Node

A region of zero electron density

Orbital

The solution to a wave equation denoted by ψ. A 3D mathematical region around an atom’s nucleus where an electron is most likely to be found

Organic chemistry

The study of carbon compounds

Pi (π) bond

The bond that forms when unhybridized p orbitals interact in a sideways overlap

Sigma (σ) bond

The bond that forms by the head-on overlap of two atomic orbitals along a line drawn between the nuclei

Skeletal structure

Structure that leaves out carbon symbols and carbon-hydrogen bonds

sp hybrid orbital

Orbital that is formed by combining one s orbital and one p orbital

sp2 hybrid orbital

Orbital that is formed by combining one s orbital and two p orbitals

sp3 hybrid orbital

Orbital that is formed by combining one s orbital and three p orbitals

Valence bond (VB) theory

Theory that states when a covalent bond forms when two atoms approach each other closely and a singly occupied orbital on one atom overlaps a singly occupied orbital on the other atom

Valence shell

An atom’s outermost shell

Acidity constant (Ka)

The exact strength of a given acid (HA) in water solution

Brønsted-Lowry acid

A substance that donates a hydrogen ion

Brønsted-Lowry base

A substance that accepts a hydrogen ion

Conjugate acid

The product that results when the base gains a proton

Conjugate base

The product that results when the acid loses a proton

Dipole moment (μ)

The magnitude of the charge Q at either end of the molecular dipole times the distance r between the charges

Dispersion force

Weak, temporary attractive forces that occur when the constant motion of electrons creates uneven charge distribution in atoms or molecules

Electronegativity (X, EN)

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

Electrostatic potential map

Visual that uses color to indicate electron-rich (red, δ-) and electron-poor (blue, δ+) regions

Formal charge

The hypothetical electrical charge assigned to an individual atom in a molecule and don’t imply the presence of actual ionic charges in a molecule

Hydrogen bond

An attractive interaction between H or an F, O, N atom

Inductive effect

The shifting of electrons in a σ bond in response to the electronegativity of nearby atoms

Intermolecular force (aka noncovalent interactions)

An attractive or repulsive force that acts between neighboring molecules, atoms, or ions

Lewis acid

Substance that accepts an electron pair

Lewis base

Substance that donates an electron pair

pKa

The negative common logarithm of the Ka

Polar covalent bond

Bond in which bonding electrons are attracted more strongly by one atom than the other, so the electron distribution between atoms is not symmetrical

Resonance form

Multiple Lewis dot structures that are used to represent a single molecule

Resonance hybrid

The actual, true structure of a molecule or ion that cannot be fully or accurately represented by a single Lewis structure