Fundamentals 2: Structure and Bonding Flashcards
what is an s orbital?
has a single lobe, centered on the nucleus.
electron density decreases the further you move away from the nucleus.
can hold up to 2 electrons, is the lowest energy orbital.
what is a p orbital?
has two lobes, dumbbell-shaped.
centered on the nucleus and separated by a node.
can hold up to 6 electrons, has a higher energy than s orbitals.
what does it mean to say orbitals are degenerate?
it means they have the same energy level.
how are molecular orbitals made?
2 atoms move closer together, their atomic orbital wavelengths begin to interact.
nuclear repulsion at first, then a covalent bond.
point of maximum attraction is the bond length.
what is constructive overlap?
2 atomic orbitals combine in phase, their wave functions add together.
a MO is made, with greater electron density between the nuclei.
wave functions reinforce each other, resulting in a stronger bond between the atoms.
what is antibonding?
when 2 AO’s combine out of phase, meaning their wave functions subtract from each other, they produce a MO with less electron density between the nuclei.
called antibonding because the wave functions cancel each other out, creating a weaker bond.
how is antibonding generated?
when two AO’s combine out of phase, meaning wave functions subtract from one another.
also through the subtraction of in-phase wave functions.
what is a nodal plane?
a plane that passes through the nucleus of an atom on which the probability of finding an electron is 0.
it represents the space where the wave functions of two atomic orbitals combine out of phase and cancel each other out.
what determines the strength of a sigma bond?
the extent of the overlap between the AO and the number of electrons shared between the atoms.
what is σ* antibonding?
when two AO’s combine out of phase to create an MO with a node.
the electrons are less stable and have higher energy.
they are weaker than sigma bonding orbitals.
responsible for double and triple bonds.
repulsion in the middle causes separation.
what is HOMO?
highest occupied molecular orbital.
has highest energy electrons that are paired/unpaired.
the orbital where the next electron added to the molecule will reside.
determines reactivity.
molecules with low energy HOMO are more stable and less reactive
why are molecules with low energy HOMO more stable?
the electrons are less reactive and less likely to participate in chemical reactions.
less likely to donate, more likely to accept electrons.
energy required to remove an electron from HOMO with low energy is high.
energy required to add an electron is low.
what is LUMO?
lowest unoccupied molecular orbital.
lowest energy and unoccupied by electrons.
determines the ability to accept electrons.
low energy LUMO = more likely to accept electrons, more reactive and less stable.
why does cylindrical symmetry of bonding and anti-bonding account for rotation around sigma bonds?
rotation around the axis of the sigma bond does not change the shape or orientation of the orbitals.
bond stays in same position as it rotates.
allows for conformations and isomers of molcules.
how do p orbitals form sigma bonds?
1 pair is end on overlap, electron density concentrated along axis of the bond, cylindrical symmetry.
2 pairs are side-on overlap to form pi bonds.
