Chapter 1 Flashcards
The energy of electron shells is _______.
Quantized
Delocalization
The spreading of electron density over a large volume of space.
What orbitals does the first shell contain?
1s
What orbitals does the second shell contain?
One 2s and three 2p orbitals
Ground-state electron configuration
The electron configuration of lowest energy
Three rules for determining the ground-state electron configuration:
- The Aufbau (“build up”) principle
- The Pauli exclusion principle
- Hund’s rule
Aufbau principle
Orbitals fill in order of increasing energy, from lowest to highest,.
Pauli exclusion principle
Requires that only two electrons can occupy an orbital and their spins must be paired.
Hund’s rule
When orbitals of equal energy are available, but there are not enough electrons to fill all of them completely, then one electron is added to each orbital before a second electron is added to any of them. The spins of single electrons in the degenerate orbitals should be aligned.
Ionization potential
The energy it takes to remove an electron from an atom or a molecule.
Electronegativity
A measure of the force of attraction by an atom for electrons it share in a chemical bond with another atom
Nonpolar covalent bond
A covalent bond in which the difference in electronegativity of the bonded atoms is less than 0.5
Polar covalent bond
A covalent bond in which the difference in electronegativity of the bonded atoms is between 0.5 and 1.9
What is the Pauling scale?
A scale of electronegativity values
Equation for formal charge
Valence e- in the neutral, unbonded atom - (all unshared e- + one half of all shared e-)
Alcohol
OH (hydroxyl) group bonded to a carbon atom.
Another term for ester:
Carboxylic ester
Can the nitrogen from an amide be bonded to other carbons?
Yes, there do not have to be hydrogens attached to the nitrogen. It can be contained within the molecule, rather than just at the end of it.
Tetrahedral bond angle:
109.5
Trigonal planar bond angle
120
Linear bond angle
180
Bent (3 regions of electron density). Description and bond angle
2 bonded pairs, 1 lone pair. <120
Trigonal pyramidal. Description and bond angle
3 bonded pairs, 1 lone pair. <109.5
Bent (4 regions of electron density). Description and bond angle.
2 bonded pairs, 2 lone pairs. <109.5
Einstein proposed that light consists of:
photons of electromagnetic radiation
The energy E of a photon =
hv
h is:
Planck’s constant
What did Louis de Broglie propose?
If light exhibits properties of particles in motion, then a particle in motion exhibits the properties of a wave. He proposed that a particle of mass m and velocity v has an associated wavelength.
The sign of the numerical value of the wave equation is called the ______, and changes in sign are referred to as _______.
phase, phase changes.
Node
Any point where the value of a solution of a wave equation is zero. Where phase changes occur.
A nodal plane
Any plane perpendicular to the direction of propagation that runs through a node.
A wave function occupies _______ and is called ______.
3-dimensional space, an orbital
Molecular orbital theory
A combination of n atomic orbital gives n molecular orbitals.
Sigma orbitals
Characterized by head-head overlap. Cylindrical symmetry of electron density about the internuclear axis. Primary bond type between two atoms. Typically made using hybrid orbitals.
pi orbitals
Characterized by sideways overlap. Electron density above and below the internuclear axis. Additional bonds found in double and triple bonds. Almost always made using atomic p-orbitals.
Valence bond theory
Involves the combination of atomic orbitals on each atoms before considering bonding. This combination is called hybridization, and the resulting atomic orbitals are called hybrid orbitals
Hybrid orbitals
Formed by the “mixing” of atomic orbitals to create new orbitals of equal energy, called degenerate orbitals.
Bonding molecular orbital
An orbital in which electrons have a lower energy in which they would in the isolated atomic orbitals
Combination of two 1s orbitals by addition of their wave functions
Sigma bonding orbital
Combination of two 1s orbitals by subtraction o their wave functions
Sigma anti-bonding orbital
Anti-bonding molecular orbital
An orbital in which the electrons in it have a higher energy than they would be in the isolated atomic orbitals. Causes repulsion of the nuclei involved
In VB theory, the bonds are localized:
between adjacent atoms rather than delocalized over several atoms as is MO theory
sp3 hybrid orbitals
The mathematical combination of the 2s atomic orbital and three 2p atomic orbitals. 25% s-character, 75% p-character
sp2 hybrid orbitals
The mathematical combination of one 2s atomic orbital and two 2p atomic orbitals. 33% s-character, 67% p-character.
sp hybrid orbitals
The mathematical combination of one 2s orbital and one 2p atomic orbital. 50% s-character, 50% p-character
Individual Lewis structures are called:
contributing structures
Rules for writing acceptable contributing structures:
- All contributing structures must have the same number of valence electrons
- Must obey the rules of covalent bonding
- Same atom connectivity
- Same number of valence electrons
Preferences for estimating the relative important of contributing structures
1: filled valence shells
2: least separation of unlike charges
3: negative charge on a more electronegative atom
How is charge delocalization depicted?
Dashed lines (the second line) between the atoms the charge can be on and a 1/2 charge on each atom.
Conjugation
A lack of an intervening atom between pi bonds or between pi bonds and lone-pair electrons
Delocalization occurs in _______ systems.
conjugated
To picture the orbitals involved in delocalized systems, use only ____ theory.
molecular orbital
The shorter the bond, the _______ the bond.
stronger
