Midterm 1 Flashcards
Wavefunction (Y)
describes the current state of a quantum mechanical system (ex. electron)
for each point x in space, |Y(x)^2| means…
the probability that the electron is at position x
Node
zero probability of finding the electron here
It doesn’t matter if Y(x) is pos. or neg. bc what matters is if…
|Y(x)^2| is large
The ground state
The state with the lowest energy
For hydrogen, the ground state is the…
1s state
Degenerate
When multiple states have the same energy
In a covalent bond, electrons are…
shared
Valence Bond Theory
explains molecular geometry in terms of atomic orbitals while keeping the idea of localized electrons
Molecular Orbital Theory
more accurate description because it allows electrons to be delocalized
Heisenberg Uncertainty Principle
the more you know about the position of an electron, the less you know about its speed
A bond is formed by…
overlapping two atomic orbitals
For bonding, good overlap =
a stronger covalent bond
Sigma bond
cylindrical symmetry around the bond axis
Sigma bonds have high…
electron density along the bond axis
Bonding diagrams
show the electron configuration of valence electrons of each atom and their bonding pairs
Pi bonds
have a nodal plane that includes the bond axis
Pi bonds have high…
electron density on either side of the bond axis
Pi bonds are formed by…
side-by-side overlap of p-orbitals that are aligned with each other
A single bond has…
one sigma bond
A double bond has…
one sigma bond and one pi bond
A triple bond has…
one sigma bond and two pi bonds
Hybrid orbitals are…
degenerate
Pi bonds hinder…
rotation around the C=C bond axis
Molecular Orbitals
are built from linear combinations of atomic orbitals
Bond Order equation
((# of e- in bonding MOs)-(# of e- in antibonding MOs))/2
Homonuclear diatomics include…
Li2 to N2
The number of molecular orbitals is…
ALWAYS the same as the number of atomic orbitals
As bond order decreases,
bond energy decreases and bond length increases
LUMO
lowest unoccupied molecular orbital
HOMO
highest occupied molecular orbital
In a nonpolar covalent bond,
the electron pair is evenly shared between both atoms
In a polar covalent bond where one atom has a lower electronegativity than the other,
the bonding and antibonding molecular orbitals are uneven mixtures of atomic orbitals
Use valence bond theory for…
sigma bonds
Use molecular orbital theory for…
pi bonds
Conjugated systems
are a collection of aligned p-orbitals that form extended molecular orbitals
The HOMO-LUMO gap is…
the smallest amount of energy that the molecule can absorb
Intramolecular forces
the chemical bonds that hold atoms together within a molecule
ionic is ________ than covalent
stronger
Intermolecular forces
interactions between molecules
IMFS are responsible for…
cohesion between molecules
Breaks IMFs
boiling
A high boiling point indicates
strong IMFs
London (Dispersion) Force
the interaction between the fluctuating dipoles
Polarizability
the tendency of molecules to generate induced electric dipole moments when subjected to an electric field
the larger the polarizability,
the larger the dipole moment
Molecules with more electrons are…
more polarizable
Heaver (larger) molecules have greater…
dispersion forces and boiling points
Hydrogen bond
the favorable interaction between a polar bond including H and NOF
Each water molecule can have up to…
four hydrogen bonds (tetrahedral order)
Surface tension
the energetic cost of creating an interface
Interface
the surface of a liquid where not all molecules are surrounded
At the interface there are…
less favorable interactions than the molecules in the bulk liquid
The stronger the surface tension,
the greater the IMFs of the liquid
The lowest energy state of a fixed amount of liquid is a…
sphere (because it has the lowest surface-to-volume ratio)
Benzyne is more reactive than benzene because the natural bond angle for sp hybridized species is
180 degrees but it has a hexagonal structure (120) at the bond angles (significant strain at triple bonded carbons)
Conjugated bonds means…
longer wavelength
11 conjugated bonds vs. 16 conjugated bonds:
16 conj. bond system would be weaker and have a slower wavelength, thus absorbing more red light. It will be bluer than the 11 conj. bond system and have a smaller HOMO-LUMO gap and lower energy.
For polar molecules, valence electrons are pulled towards…
the more electronegative atom
Moleules with a bond order greater than zero are..
stable
Diamagnetic
electrons are paired
Paramagnetic
electrons are unpaired
