exam 3 Flashcards
(84 cards)
1
Q
resonance structures
A
a resonance structure is when a lewis config has 2 or more equivalent structures - this averages out the bonds
2
Q
the most important(best) resonance structure is determined by:
A
the one with all the bonds closest to 0
3
Q
polar covalent bonds:
A
occurs when there is uneven yoke-age electronegativity wise (N - O vs N-N which is purely covalent)
4
Q
formal charge calculation:
A
valence e - num marks around the atom(electrons and bonds)
5
Q
number of bonds:
A
(Needed e - available e)/2
6
Q
the polarity of a bond increases by:
A
the change in electronegativity
7
Q
what is a sigma bond?
A
A bond made by sharing bond orbitals
8
Q
what is a pi bond?
A
A bond made by the sideways overlapping of p-orbitals
9
Q
what is a double bond made of?
A
one sigma and one pi
10
Q
what is a single bond made of?
A
one sigma bond
11
Q
what is a triple bond made of?
A
one sigma and two pi
12
Q
Which is stronger? pi or sigma?
A
Pi bonds are stronger
13
Q
Dipole moment =
A
the magnitude of charges * distance
14
Q
How to find steric numbers:
A
num lone electron bonds + num atoms bonded to central atom
15
Q
if the steric number is 4:
A
the angle is 109.5
16
Q
if the angle is 120:
A
the steric number is 3
17
Q
if the steric number is 2:
A
the angle is 180
18
Q
if there is no angle:
A
the number is 1
19
Q
how to tell if a molecule is polar (by structure)
A
if it is NOT symmetric and the dipole moment is NOT 0
20
Q
A bond is polar if
A
the difference in electro-negativity is greater than 0.4
21
Q
hybridized sp3 orbital can bind to:
A
4 - because of 4 regions of electron density
22
Q
how many pi bonds can an sp2 orbital have?
A
1 - because of one open orbital for side-on overlap
23
Q
2 sp hybridized atoms (N2) are bonded. how many pi and sigma bonds are there?
A
2 pi, 1 sigma (triple bond)
24
Q
Identify the orbitals used by the bolded atom in acetone (CH3COCH3).
A
there are 3 single bonds, so 3 pure pz bonds
25
A molecule has five regions of high electron density around the central atom. One of these is a lone pair and the other four are bonded pairs. What is the hybridization of the central atom?
sp3d
26
What is the hybridization of the second carbon atom (bolded) in H2C*C*CH2?
sp
27
how to find the hybridization number:
sigma bonds + lone e pairs
28
how to find bond order:
bonds/resonance stucture num
29
The energy of a molecule is determined by the:
distance of the nuclei - this energy tells us the bond length and energy
30
Molecular orbitals with lower energy than atomic orbitals are:
bonding
31
Molecular orbitals that are equal in energy to atomic orbitals are:
non-bonding
32
molecular orbitals that are higher in energy than atomic orbitals are:
anti-bonding
33
Sigma bonding is due to the end-to-end overlap of orbitals having __________ interference (in phase). All σ-bonding is "on axis" meaning the electron density is centered directly between the two bonding nuclei.
constructive
34
_____ are places of zero electron density between atoms.
nodes
35
nodes occur more often in what level of energy for a molecular orbital?
High energy - common in antibonding situations
36
another method for bond order:
The bond order is equal to 1/2 the number of electrons in bonding orbitals - the number of electrons in anti-bonding orbitals.
37
We can think of non-bonding orbitals as essentially the __________ we would get from the Lewis dot structure.
lone pairs
38
the HOMO LUMO gap is:
the lowest energy electronic excitation that is possible in a molecule. The energy of the HOMO-LUMO gap can tell us about what wavelengths the compound can absorb.
39
HOMO LUMO gap found by
the highest occupied molecular orbital or HOMO - the lowest un-occupied molecular orbital or LUMO
40
t/f most molecules are paramagnetic
FALSE - most are diamagnetic
41
What is the possible geometry of the hybridization sp?
linear
42
What is the possible geometry of the hybridization sp2?
Trigonal planar
43
What is the possible geometry of the hybridization sp3?
tetrahedral/trigonal pyramidal
44
What is the possible geometry of the hybridization sp4?
triangular bipyramidal
45
As bond order increases, what happens to bond length, stability, and energy?
the length shortens, it is more stable, and the energy rises
46
T/F Bonding orbitals are lower in energy than their corresponding anti-bonding orbitals.
TRUE!!
47
T/F Adding electrons to anti-bonding orbitals destabilizes molecules.
True
48
T/F Unlike when we fill atomic orbitals, we DON'T use Hund's Rule to fill molecular orbitals.
False
49
Which dye has the greater HOMO LUMO gap? 670nm or 560nm? why?
The smaller wavelength will have the higher frequency and, thus, the higher energy transition. In other words, the dye that absorbs the smaller wavelength light will have the greater difference in energy between its HOMO and LUMO (the larger HOMO-LUMO gap).
50
An antibonding orbital is formed when:
the overlap of the corresponding atomic orbitals leads to destructive interference.
51
Consider the molecule B2. What is the magnetism and number of unpaired electrons in B2?
paramagnetic, 2
52
every molecule has __________ forces
dispersion
53
What is a dipole-dipole force?
This occurs for polar molecules as they have a permanent dipole moment. a dipole is defined as two opposite charges separated by a distance. Therefore, a molecule with a dipole has a "positive end" and a "negative end."
54
when can there be hydrogen bonds?
occurs in polar molecules when a hydrogen atom is bonded to a highly electronegative atom - N, O, or F
55
what kinds of molecules only have dispersion forces?
Nonpolar covalent molecules
56
all 5 electron geometries are non-polar if:
all the positions are the same atom (PF5)
57
make cards off of VSEPR video
fuckin do it
58
vapor pressure goes down as:
IMFs go up
59
viscosity (resistance to flow) goes up as
the intermolecular forces (IMF) goes up and number of atoms goes up (harder to slip by)
60
Which would you expect to have the lowest vapor pressure at room temperature?
1: CH2Br2
2: CH4
3: CF4
1, because CH2Br2 is a polar compound. All of the other compounds are non-polar. Thus, CH2Br2 would have the strongest intermolecular forces and would therefore have the smallest vapor pressure.
61
the more polar, the higher the ___
IMFs
62
match the orbital hybrids to the angles - 180, 90, 120, and 109:
- sp
- sp2
- sp3
- sp3d
sp - 180
sp2 - 120
sp3- 109 (ish
sp3d - 90
63
covalent or network solids have ____ melting points and are held together by _____ bonds
high, covalent
64
Ionic solids have ____ melting points, are held together by _____ bonds, and, when put an aqueous solutions can _______
Medium, ionic, conduct electricity
65
Metallic solids have _____ melting points, are held together by ______ bonds, and are ________
low, metallic, malleable
66
Molecular solids are held together by _____. this cause them to be _______, and have ______ melting points.
IMFs, nonconductive (electrons are localized, low
67
A london dispersion force is
is the weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force is sometimes called an induced dipole-induced dipole attraction.
68
Which of the following molecules are likely to form hydrogen bonds?
1. CH3CH2OH
2. CH3COOH
3. CH3CHO
4. CH3OCH3
1 and 2 - the OH branches are only in them
69
Dispersion forces decrease with increasing molecular size T/F
False
70
Polarizability increases with:
Large, negatively charged ions, such as I- and Br-. (they are more likely to form crystals because of easier to move electron clouds)
71
Permanent dipole-dipole interactions
stronger than London forces and occur between polar-covalent molecules.
72
H-bonds
very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electronegative atoms - F, O, or N.
73
Ion-ion interactions are
the strongest due to extreme charge separation and occur between ionic molecules. They can be thought of as both inter- and intramolecular bonding.
74
Covalent bonds are
The strongest, but they are specifically a type of intramolecular bonding, not intermolecular bonding.
75
If there are no Hydro bonds, _____ will be the most significant IntERmolecular bonding in a polar molecule.
dipole-dipole
76
If there are no Hydro bonds, _____ will be the most significant IntERmolecular bonding in a very large molecule.
dispersion
77
the higher the IMFs, the ______ the boiling point
higher
78
iodine makes dispersion forces a lot more likely?
yes! dispersion increases as electrons increase (velcro)
79
Hydrocarbon memory trick- formula
c(n)h(2n+2)
80
hydrocarbon memory trick till butane!
many elephants play bach (cred to alexander funk)
81
a star * on an orbital (sigma or pi) means it is
nonbonding
82
what is the bond MO config for He 2
σ2(1s) σ*2(1s)
83
what is the bond MO config for O2
σ2(1s) σ*2(1s) σ2(2s) σ*2(2s) σ2(2p) π2(2p) π*2(2p)
84
what is the bond MO config for HF
σ2(1s) σ*2(2s) π2(2p) π*2(2p)
