Midterm 2 Flashcards
what is valence bond theory
Valence bond theory: Covalent bonds form through the sharing of electrons by adjacent atoms, when the electron orbits of the two atoms overlap.
how does the quality of valence electron overlap affect bonding
The energy of a covalent bond system depends on the quality of the overlap. If the two nuclei get too close together than the repulsive forces between them increase the energy of the system.
what are hybrid orbitals
A combination or merge of multiple different orbitals
Hybrid atomic orbitals allow us to apply the ideas of orbital overlap and valence bond theory to Polyatomic molecules.
When combining atomic orbitals to make hybrid orbitals, n atomic orbitals make n hybrid orbitals.
describe sp orbitals
For elements like beryllium which don’t have singly-occupied orbitals in its ground electronic state it will have trouble forming bonds. So it can promot a 2s electron to 2p, then both the 2s and 2p electrons become 2 different sp hybrid orbitals.
They have two lobes, one larger one, one smaller
how does phase affect hybrid orbitals
Orbitals of any kind can have a positive and / or negative portion based on the wave function in that region. When making hybrid orbitals, waves of the same sign get added in magnitude (constructive), and those opposite lose magnitude (destructive).
what are very simplified depictions of hybrid orbitals like and why
Usually only the larger lobe of a hybrid orbital interacts with other orbitals, so in very simplified depictions of Hybrid orbitals it might be the only part shown.
what are SP2 orbitals
when one s orbital and two p orbitals are hybridized they form three SP2 orbitals
these looks pretty similar to SP orbitals with one large lobe facing out in a trigonal planer shape, and one small lobe closer to the nucleus.
what are SP3 orbitals
When one s orbital and three p orbitals are hybridized they form four SP3 hybrid orbitals
the large lobes face out in a tetrahedral shape
what are SP3D orbitals
one s orbital + 3 p orbitals + one d orbital makes 5 SP3D orbtials (in a trigonal bipyramidal shape)
what are SP3D2 orbitals
one s orbital + 3 p orbitals + two d orbitals make 6 SP3D2 orbtials (in an octahedral shape)
what are sigma bonds
So far the covalent bonds have all been sigma bonds
These have head to head overlap
and cylindrical symmetry of electron density about the internuclear axis
how does the number of electron domains tell us the Hybridization state of an atom
2 e- domains = Sp
3 e- domains = sp2
4 e- domains = sp3
5 e- domains = sp3d
6 e- domains = sp3d2
what are pi bonds
When describing multiple bonding, we must invole pi (π) bonds
these have side to side overlap
and electron density above and velow the internuclear axis
In single, double, and triple bonds what types of bonds do they have
Single bonds are always a sigma bond, since overlap is greater, making the bond stronger and more energy lowering
In multiple bonds, one is a sigma bond, the rest are pi bonds
So in triple bonds there is one sigma bond, then two pi bonds (one above the plan, and the other in the plane)
when are electrons delocalized
For atoms with resonance structure,
for an example the nitrate ion where all the atoms have a p orbital, and the three p orbitals of the oxygen atoms overlap with the p orbital on the central nitrogen. The πelectrons are delocalized throughout the ion.
Similar for benzene where the π electrons are delocalized throughout the ring.
why do we need molecular orbitals
Lewis structures, VSEPR theory, and hybridization still do not explain a few things.
ex: why does O2 interact with magnetic fields
why are some molecules coloured
how do we explain metallic bonding
Molecular orbital theory helps explain some of these observations
what is the difference between atomic and molecular orbitals
Electrons in atoms are found in atomic orbitals
electrons in molecules are found in molecular orbitals
how are molecular orbitals similar to atomic
Molecular orbitals are similar to atomic orbitals in a few ways:
- each contain 2 electrons with opposite spins
- each has a definite energy
- electron density distribution can be visualized with contour diagrams
how do we know how many molecular orbitals there are
when n AOS overlap, n MOs form, for hydrogen 1s (H) + 1s (H) must result in 2 MOs
what are the two different types of molecular orbitals
a destructive combination of AOS creates and anti-bonding orbital
while a constructive combination of AOS creates a bonding orbital
both have their electron density centred around the internuclear axis
in what order do electrons fill molecular orbit
Electrons will fill Molecular orbits starting with the bonding orbitals, each MO has space for 2 electrons
and they start from the most bonding bonding orbitals and move up
how do molecular orbitals tell us the H2 can exist and He2 not
So for hydrogen-hydrogen, it has 1 antibonding Orbital, and 1 bonding orbital. But since it only has 2 electrons, they both end up in the bonding orbital.
Since there is not antibonding electrons to cancel out the bonding ones, the H2 molecule is possible
For He2, there is 4 electrons to fill 2 MOS. meaning both anti-bonding and bonding orbitals hold 2 electrons. And they cancel out, preventing the He2 molecule from forming.
what is the formula for bond order
Bond order = 1/2 (no. of bonding electrons - no. of antibonding electrons)
how does molecular bonding explain solid sodium metal
Consider the element sodium, when a large number of sodium atoms are bonding, they each have 1 MO and 1 electron. So the total number of MO is equal to the total number of sodium atoms. There is also the same number of electrons to fill these MOs, but, since each MO can hold 2 electrons, they are only half fulled. And since the bonding ones fill up first, any number of Sodium atoms can bond together. creating solid sodium metal.
This is called band theory, since as you add more Na atoms to the chain, the space between orbitals gets smaller till you have a band.
