Midterm 3
Which statement best describes an O3 molecule? 1. Each atom in ozone is connected to another atom by a bond having a bond order of 1.5. 2. The double bond in ozone switches back and forth between the two outer oxygen atoms. 3. An ozone molecule contains one single bond and one double bond.
1. Scientists previously believed that a molecule such as ozone switched rapidly back and forth between its different resonance forms. More recent experiments have shown that the molecule actually assumes the average of all the resonance forms, with the electrons delocalized over all three oxygen atoms as shown in the following diagram.
What are five factors that affect bond energy?
1. size of atom 2. difference in electronegativity 3. number of lone pairs present on bonded atoms 4. number of bonds 5. s orbital contribution creates stronger bonds
Number of bonding electrons for Cl in ClO₃-?
10
What is z effective of Ca²⁺?
10
Carbonate ion is resonant, COCl₂ is not. Predict the bond angles within both.
120° for everything in carbonate Bond angle b/n Cl, C and Cl will be less than 120°, the other two will be greater than.
How many double bonds in H₂S₂O₃?
2
What is the core charge of Ca²+?
20 - 10 = 10
Why is the outer electron configuration of Cr 4s¹3d⁵ and why is Cu 4s¹3d¹⁰?
3d and 4s energy levels are closely spaced to begin with; completely or half filling a sublevel lends additional stability
What is the partial charge on the carbon atom in CN? EN for C is 2.54, EN for N is 3.07
4 - 1 - 6(2.54/(2.54 + 3.07))
The charge associated with each side of an HF molecule is 6.93×10⁻²⁰C. The charge on a single electron is 1.60 x 10⁻¹⁹C. How do you find percent ionic character, and what does the value mean?
43.3% If the HF molecule were 100% ionic, the F side would have a charge of −1, whereas the H side would have a charge of +1. Instead, the F side has a partial charge of − 0.433, whereas the H side has a partial charge of +0.433.
There are no double or triple bonds in P₄. How many single bonds does it have?
6
If you include structures in which sulfur has an expanded octet and exclude structures with triple bonds, how many resonance structures can be drawn for sulfur trioxide, SO3?
7
What bond angle do you expect from the unhybridized orbitals in PH₃?
90°
Why does Sb have 5 valence electrons?
Antimony (Sb) has an electron configuration of [Kr] 4d¹⁰5s²5p³ . If we look at this notation, we see the highest energy level is n = 5, and within that n = 5, there are 2 electrons in the s orbital and 3 electrons in the p orbital. Thus, there are 5 valence electrons (2 from 5s and 3 from 5p) in this n = 5 energy level.
which element has higher ionization energy, B or Be?
Be
Rank from highest to lowest magnitude of lattice energy: LiCl, MgO, Na₂O, Na₂S, BeO
BeO, MgO, Na₂O, Na₂S, LiCl
Where is the dipole moment for SF₄?
Between the two F atoms in the equatorial axis
Why does C go in the middle of the two O's in CO₂?
C is less electronegative
draw the two isomers of CH₃NO₂
CH₃ - NO₂ CH₃ - O - N = O
Out of CH₃OCH₃, CH₃OH, and H₂O, which has the largest bond angle and which has the smallest? (think of O as always being in the middle, having tetrahedral electron geometry for all)
CH₃OCH₃ has the largest bond size and H₂O has the smallest
pick the one with the highest boiling point: CH₃OH or CH₃SH.
CH₃OH b/c of hydrogen bonding
Compare the boiling points of CH₃OH, N₂, and CO.
CH₃OH has the highest boiling point because it will have hydrogen bonds. CO is polar and N₂ is not, so it'll have the next highest boiling point
CN and CN⁻: which has the larger dipole moment?
CN⁻ has a larger dipole moment because its C has a larger (magnitude of) partial charge Remember: partial charge is different from formal charge b/c it doesn't assume that the electrons are shared equally between two different atoms w/ different electronegativities
Of KI and CaO, which has a bigger lattice energy and by how many times?
CaO, 4 times (PE = k*q1*q2/r)
Describe what occurs when your breath is bubbled through calcium hydroxide solution and write a plausible balanced chemical equation for this reaction.
Ca²⁺ + CO₃²⁻ → CaCO₃ carbon dioxide dissolves in water to form carbonate ions that then react w/ Ca²⁺ to create CaCO₃
In the Lewis Structure of HSO₃⁻, where is the H positioned? Describe the bonding between the S and O atoms
Connected to one of the O atoms, not to the sulfur atom. Two S-O bonds, one S=O bond
rank C₂H₅OH, HCl, and C₃H₆ in order of increasing boiling point
C₃H₆ < HCl < C₂H₅OH
Consider the metals in the first transition series. Use periodic trends to predict a trend in density as you move to the right across the series.
Density increases bc though e- are added successively across the period, they go into the 3d subshell which isnt a part of the outermost principal energy level. So radius doesnt increase much while mass definitely does.
Based on periodic trends alone, is P or Kr bigger?
Impossible to determine
Why does N have smaller radius than P?
Increase in principle quantum numbers
Place these metals in order of INCREASING reactivity: Rubidium, Potassium, Strontium, Magnesium
Mg < Sr < K< Rb
which element has higher first ionization energy, N or O?
N
Which elements bonded to hydrogen cause hydrogen bonding?
N, O, F
Which has a higher ionization energy, N or O?
N, because its shell is half-filled
Out of Na, Li, Mg and Ca, which is the most reactive and why?
Na, because its radius is greater than Li and Mg, while its Zeff < Mg and Ca, meaning less work will be required to remove outer electron, meaning more reactivity
Why does sodium and chloride combine as NaCl and not Na₂Cl or NaCl₂? (give reason in terms of ionization energy)
Na: 3s e⁻ has low ionization energy, but the next one is really high b/c it's a core e⁻ Cl: electron affinity for one e⁻ is high b/c added e⁻ completes valence shell, low for the second one
Which has the highest boiling point? Br₂, NaBr, HBr, or BrF?
NaBr
Rank the following compounds in order of decreasing boiling point: sodium fluoride (NaF), carbon tetrafluoride (CF₄), and chloromethane (CH₃Cl)
NaF, CH₃Cl, CF₄ NaF is ionic, so it has the highest boiling point
Is Cd²⁺ paramagnetic?
No
Woukd an element's isotopes vary in their atomic radii?
No bc negligible size doesnt increase atomic size and neutrons have no charge and wouldnt attract e-
Pauli Exclusion Principle
No two electrons in the same atom can have the same four quantum numbers. (But they can have the same first three, and then opposite spins.)
A tank containing liquid butane and one containing liquid propane are sitting adjacent to one another. Each tank is equipped with a regulator with a pressure gauge. Will the pressure readings change when more liquid is added to the tanks?
No, because only temperature, the type of solute, and the type of liquid affect the vapor pressure. The amount of liquid, the atmospheric pressure and the surface area don't affect the vapor pressure.
As electrons move further away from the nucleus, does the effective charge of the nucleus decrease? If not, what does?
No: just as a magnet's charge doesn't decrease if you move further away or closer to it, the Zeff remains constant. However, the force felt by the electron can change with the distance. The equation expressing force, k * q₁ * q₂ / r, explains this trend.
Which has a stronger bond, F₂ or O₂?
O₂
What determines the height of each peak in a PES spectrum?
Relative # of e⁻ ejected by a specific photoionization energy
guanidinium (C(NH₂)₃⁺) cation has trigonal planar shapes about the C atom and all 3 N atoms, but its resonance structures feature lone pairs on two of the N atoms. How can trigonal planar shapes exist if there are lone pairs that seem to create tetrahedral shapes?
Resonance structures, so they don't actually form tetrahedral b/c electron lone pairs move around just as bonds do
Do resonant and nonresonant molecules have the same geometry? Are the bonds equivalent or skewed in each type of structure?
Resonant and nonresonant molecules have the same geometry, the bonds are equivalent in the resonant structures, and the bond angles would be skewed for the nonresonant structures.
In S2Cl2 what is the hybridization of the interior atoms and what is the geometry based on VSEPR theory?
Sp3, bent
What is the molecular geometry of BrF4-?
Square planar
molecular geometry of ClF₃?
T-shape
Why is the energy of the 2s orbital lower than the energy of a 2p orbital?
The 2s orbital penetrates closer to the nucleus and experiences more of the nuclear charge.
Out of the diatomic halogen molecules, why is F₂ not the strongest bond, even though it's the shortest bond?
The F-F bond length is so short that the lone pairs of electrons on the fluorine atoms repel each other and weakens the F-F bond.
Why is the 4s orbital lower in energy than the 3d orbitals?
The effect of penetration: there's a much higher probability of the electron being found very close to the nucleus, in the area past the shielding by 1s orbitals. The d orbitals, on the other hand, have radial distribution function that lies outside that of the 1s orbital, so the nuclear charge from the 1s orbital shields the d orbitals, resulting in a higher energy.
Between the two of these, Cs(g)→Cs⁺(g) + e⁻ and Cl(g) + e⁻→ Cl⁻(g), which absorbs energy and which releases?
The first one absorbs energy, the second one releases energy
Predict how bond angles in NO₂ might differ in relation to the ideal angles, justify your prediction
The hybridization is sp² but the one lone electron repels less than a lone pair and a bonding pair, which would mean the bond angle would be significantly more than 120°
Why are ns electrons lost before the (n-1)d electrons in ionization of transition metals?
The ns and (n-1)d orbitals are very close in energy with ns orbitals being slightly less. However, in the transition metals, the (n-1)d orbitals begin to fill and the nuclear charge actually stabilizes them more so than ns orbitals because (n-1)d orbitals are closer than the ns orbitals to the nucleus.
Na has a much lower first ionization energy than Ne. Why?
The outer electron in Na is farther away from nucleus than the outer electron in Ne
In VSEPR theory, the trend of decreasing bond angle in CH₄, NH₃ and H₂O is accounted for by the greater repulsion of lone pair electrons compared to bonding pair electrons. How would this trend be accounted for in valence bond theory?
The presence of lone pairs, which exist in their own sp³ orbitals, reduces the tendency for the central atom's orbitals to hybridize. As lone pairs are added, the bond angle moves further from 109.5° hybridized angle and closer to the 90° unhybridized angle.
Compare the dispersion forces between CH₃OH, N₂, and CO.
They all have similar forces because they have similar molar masses
As ionic radii increases down a column, what happens to the lattice energy?
They become less negative, because the ions can't get as close to each other
Why does BBr₃ violate the octet rule?
To satisfy the octet rule, the compound would require one double bond between B and Br, which would create a more negative charge on B and less negative charge on Br, which is the more electronegative element. Thus, B will probably not have an octet.
What kinds of atoms tend to form covalent bonds?
Uncharged nonmetals
why does SAP absorb urine in baby diapers?
Urine is mostly water, so some of the sodium ions can diffuse into it, and the repulsion between the oxygen atoms forces the SAP to lengthen and expand, representing absorption. The only other main thing in urine is urea, which isn't ionic and won't interfere with the above process (ionic compounds cause SAP to dissolve, because the concentration of ions inside, outside the coils becomes more similar and SAP enters into solution)
Are the bonds in NH₃ shorter than the bonds in NF₃?
Yes
Is COF2 polar?
Yes
What's the e⁻ configuration of Cu?
[Ar]3d¹⁰
Hydrogen bonding occurs when
a hydrogen atom is covalently bonded to an N, O, or F atom
bond order
average number of bonds of the same pair of atoms in a compound
what properties do ionic compounds tend to have?
charged particles that move, conduct electricity
contrast the effects of core electrons and outermost electrons on shielding
core electrons shield the outermost electrons outermost electrons do not shield each other (nearly as much)
According to Coulomb's Law, what happens to potential energy of two oppositely charged particles as they get closer together?
decreases
when molar mass increases and all other variables are constant, what else increases?
dispersion force -- because there are more electrons distributed over a greater volume
when is a material conductive?
either contains metal elements or contains ions
Based on µ = q r, which has more of an effect on the dipole moment - the bond length (distance) or the electronegativity difference?
electronegativity difference
aufbau principle
electrons enter orbitals of lowest energy first
Hund's rule
electrons prefer their own seat (orbital) in bus (subshell)
Which of the following clusters of orbitals could form a trigonal bipyramidal shape in the valence shell of an isolated atom or one about to enter into bonding with other atoms?
five sp³d orbitals three sp² orbitals and one p orbital
how is covalent radius different in nonmetals and metals?
metals: 1/2 distance b/n two of the atoms next to each other in a crystal of the metal nonmetals: 1/2 distance b/n two of the atoms bonded together
connect solubility of metal w/ reactivity of metal's hydroxide
more reactive metal has a more soluble hydroxide
Least lattice energy means
most negative
Does BBr₃ obey the octet rule?
no
Does PF₅ obey the octet rule?
no
describe Lewis Structure of NO₂
oxygen 1: 6 valence, 1 bond nitrogen: 1 valence, 3 bonds oxygen 2: 4 valence, 2 bonds
Why can't sp³ and sp³d² form at least one pi bond?
pi bonds require unhybridized p orbitals to overlap, these p orbitals have all been hybridized
ψ (x,y,z)
probability that e- is at position (x, y, z) gives ψ (n, l, ml , ms)
nonbonding atomic/van der Waals radius
radius of atom when unbonded
atomic radius
set of average bonding radii
The lattice energy for CsCl is -657 MJ/mol while th elattice energy for BaS is -3500 MJ/mol. Is the bond distance of BaS greater or smaller than that of CsCl? By how much?
smaller, it's 3/4 that of CsCl (-657 MJ/mol * 2 * 2) / (x * r) = -3.50 * 10³ MJ/mol
In cumulene, what types of orbitals overlap (linear chain of 4 C's double bonded to each other, the ones on the endhave two H bonded on)
sp/sp s/sp² p/p sp/sp²
how to calculate approximate bond length of two covalently bonded atoms?
sum their atomic radii
inner electron configuration
that of the noble gas that precedes it e.g. for Cl, represent the inner e- configuration with [ Ne ]
miscibility
the ability to mix without separating into 2 separate phases
Consider the metals in the first transition series. Use periodic trends to predict a trend in density as you move to the right across the series
the density will increase -- electrons are being added to the 3d orbital, which isn't the outermost, so the atomic radius will not change much but the amount of mass inside will
lattice energy
the energy released when 1 mol of an ionic crystalline compound is from gaseous ions
hard water has deposits rich in Mg and Ca -- why does it leave a film on dishes?
the ions react w/ carbonates from dissolved CO₂ to form a precipitate
what ultimately determines the magnitude of dispersion force?
the size of an electron cloud, which determines how easily the electrons can polarize in response to an instantaneous dipole, which in turn determines the magnitude
how is van der Waals radius different from covalent radius?
van der Waals: half the internuclear separation between two non-bonded atoms on their closest approach covalent: half of the distance between two singly bonded atoms of the same element
Does CO₃²⁻ obey the octet rule?
yes
Does CS₂ obey the octet rule?
yes
is SCl₂ polar?
yes