Ch 1 - Chem Review Flashcards
Organic compounds contain
carbon atoms
Constitutional isomers
share the same molecular formula but have different connectivity of atoms and different physical properties.
Each element will generally form a predictable number of bonds.
Carbon is generally tetravalent, nitrogen trivalent, oxygen divalent, and hydrogen and the halogens monovalent.
covalent bond
results when two atoms share a pair of electrons.
Covalent bonds are illustrated using Lewis structures,
in which electrons are represented by dots.
Second-row elements generally obey the octet rule,
bonding to achieve noble gas electron configuration.
lone pair.
A pair of unshared electrons
formal charge
occurs when atoms do not exhibit the appropriate number of valence electrons; formal charges must be drawn in Lewis structures.
Bonds are classified as
(1) covalent, (2) polar covalent, or (3) ionic.
Polar covalent bonds exhibit induction, causing the formation of partial positive charges and partial negative charges
Electrostatic potential maps present a visual illustration of partial charges.
Quantum mechanics
describes electrons in terms of their wavelike properties.
wave equation
describes the total energy of an electron when in the vicinity of a proton. Solutions to wave equations are called wavefunctions(W) , where W^2 represents the probability of finding an electron in a particular location.
Atomic orbitals
are represented visually by generating three-dimensional plots of W^2; nodes indicate that the value of W is zero.
electron density
An occupied orbital can be thought of as a cloud
Electrons fill orbitals following three principles:
(1) the Aufbau principle, (2) the Pauli exclusion principle, and (3) Hund’s rule. Orbitals with the same energy level are called degenerate orbitals.
Valence bond theory
treats every bond as the sharing of electron density between two atoms as a result of the constructive interference of their atomic orbitals. Sigma (σ) bonds are formed when the electron density is located primarily on the bond axis.
Molecular orbital theory
uses a mathematical method called the linear combination of atomic orbitals (LCAO) to form molecular orbitals. Each molecular orbital is associated with the entire molecule, rather than just two atoms.
The bonding MO of molecular hydrogen results from
constructive interference between its two atomic orbitals
The antibonding MO results from
destructive interference.
atomic orbital
is a region of space associated with an individual atom, while a molecular orbital is associated with an entire molecule.
Two molecular orbitals are the most important to consider:
(1) the highest occupied molecular orbital, or HOMO, and (2) the lowest unoccupied molecular orbital, or LUMO.
Methane’s tetrahedral geometry can be explained using
four degenerate sp^3-hybridized orbitals to achieve its four single bonds.
Ethylene’s planar geometry can be explained using
three degenerate sp2-hybridized orbitals. The remaining p orbitals overlap to form a separate bonding interaction, called a pi bond. The carbon atoms of ethylene are connected via a sigma bond, resulting from the overlap of sp2-hybridized atomic orbitals, and via a pie bond, resulting from the overlap of p orbitals, both of which comprise the double bond of ethylene.
Acetylene’s linear geometry is achieved via
sp-hybridized carbon atoms in which a triple bond is created from the bonding interactions of one sigma bond, resulting from overlapping sp orbitals, and two pie bonds, resulting from overlapping p orbitals.