VSEPR Theory
What is the molecular geometry of H2O and why?
Bent, there are four charge clouds - two lone pairs, two bonds. When only accounting for the bonds this is a bent geometry.
What is the state function represents the heat change of a system at constant pressure, and is commonly reported in kJ/mol for reactions? Include the name AND the symbol.
Enthalpy (ΔH)
Draw an example of a lewis structure with bent bond geometry.
examples: H2O, SO2, O3, etc.
What are the intermolecular forces present in H2? You must name all.
London dispersion/Van der Waals
What are the two kinds of bonds present in ALL compounds (except ionic)? What are single and double bonds made of?
Single bond - one sigma bond
Double bond - one sigma bond, one pi bond
Provide the bond angles for each:
Linear:
Trigonal planar:
Tetrahedral:
Provide the bond angles for each:
Linear: 180 degrees
Trigonal planar: 120 degrees
Tetrahedral: 109.5 degrees
When you do a cold plunge, you shiver and the ice begins to melt more rapidly.
Is this an endothermic or exothermic process, if your body is the system? If so, what happens to enthalpy in reference to the system? You must provide what is happening to the symbol (mathematically?)
This is an exothermic process. This means -ΔH or ΔH < 0.
Draw the lewis structure for: NH3. Explain the hybridization (for the central atom), bond geometry, and electron geometry.
bond geometry: tetrahedral
electron geometry: trigonal pyramidal
hybridization: three bonds + one lone pair = sp3
What are the three intermolecular forces that you learned about?
Hydrogen bonding, dipole-dipole, LDF/Van Der Waals
There IS NONE! All are electrons for H are contained within s orbitals! However, the C contains sp3 hybridization.
Name all the possible electron geometries you learned about.
Trigonal planar, tetrahedral, trigonal bypyramidal, octahedral
You do 46 J of work on a system that originally contains 507 J of energy. What is the energy of the system?
A system with originally 507 J of energy does 46 J of work on you. What is the energy of the system?
Use the work equation!
∆𝐸 = 𝑞 + 𝑊
1 - 553 J
2 - 461 J
Draw an example of a lewis structure with octahedral electron geometry.
SF6, BrF5, XeF4, etc.
Give an example of a molecule with ALL 3 intermolecular forces that we talked about (you can choose to either do this in one molecule, or you can do it in multiple. If you choose multiple molecules, you must order them in terms of IMF strength and explain why).
Example in slide 9.
Name and draw an example lewis structure with every version of orbital hybridization you learned about (you can draw more than one structure).
see example in slide 12
On the following compound, (slide 5), circle and label the electron geometry at each atom.
Answer in slides (6)
Glass (c = .840 kJ/kg·°C), diamond (c = 510 J/kg·°C), graphite (c = 0.71 J/kg·°C), and gold (c = 0.129 J/kg·°C) are all subjected to a hot stove for five seconds. Which substance can you predict will heat up the least? Which one can you expect to heat up the most? Explain why for both.
Least --> Glass has the highest specific heat of all (did you catch I put the units as kJs instead of Js?), Meaning it takes MORE energy to heat it up.
Most --> Gold has the lowest specific heat of all , meaning it takes LESS energy to heat it up.
Draw three compounds with the 3 possible electron/bond geometries possible for a central atom with 6 substituents.
must have geometries of: octahedral, square pyramidal, square planar.
Predict whether or not the molecules would be liquid, gas or highly volatile liquid (vaporizes easily) by labeling the dominant IMF. See slide 7.
Answer in slides.
Fill out the following diagram (see slide 13) You get 7 minutes for this!!!
slide 14
A 12.0 g sample of an unknown substance is heated. It requires 75.6 J to raise its temperature from 20.0°C to 35.0°C.
What is the most likely identity of the substance?
a) ethylene glycol (c = 2.42 J/kg·°C)
b) xenon tetrafluoride (c = 118.39 J/kg·°C)
c) water (c = 4.18 J/kg·°C)
d) osmonium tetraoxide (c = 0.35 J/kg·°C)
C (see slide 16)
Draw an example of a compound containing EACH of the following in ONE compound: trigonal pyramidal bond geometry, tetrahedral electron geometry
Will decide correct answer
Four compounds have similar molar masses:
1) CH₃CH₂OH
2) CH₃OCH₃
3) CH₃CH₂CH₃
4) HOCH₂CH₂OH
Despite their comparable sizes, these molecules have dramatically different properties. Rank the compounds in terms of IMF strength (lowest to highest) and then explain what the properties of the compounds look like towards the bottom and top of the list.
IMF strength (lowest to highest): (3) - CH₃CH₂CH₃, (2) - CH₃OCH₃, (3) - CH₃CH₂OH, (4) - HOCH₂CH₂OH
At the bottom of the list, the compounds are likely volatile and gaseous. At the top, the compounds get more likely to be liquid and nonvolatile.
Draw an orbital diagram representing double bond overlap. You must show the specific shape the orbitals form during overlap to form a pi bond, not just a lewis structure. Optional: you man use the compound O2 to get you started.
See slides (slide 4)