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For more information, please see full course syllabus of General Chemistry
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Intermolecular Forces & Liquids
- The main types of IMF are ion-induced dipole, dispersion, dipole-dipole, and hydrogen bonding.
- IMF can exert strong influence on a liquid’s physical properties, such as boiling point and vapor pressure.
- By using IMF, we can make a strong educated guess of the relative volatility of a liquid.
Intermolecular Forces & Liquids
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
- Intro
- Lesson Overview
- Introduction
- Intermolecular Forces of Polar Molecules
- Ion-dipole Forces
- Example: Salt Dissolved in Water
- Coulomb's Law & the Force of Attraction Between Ions and/or Dipoles
- IMF of Polar Molecules cont'd
- IMF of Polar Molecules cont'd
- IMF of Polar Molecules cont'd
- IMF of Nonpolar Molecules
- IMF of Nonpolar Molecules cont'd
- IMF of Nonpolar Molecules cont'd
- Properties of Liquids
- Standard Molar Enthalpy of Vaporization
- Trends in Boiling Points of Representative Liquids: H₂O vs. H₂S
- Properties of Liquids cont'd
- Properties of Liquids cont'd
- Properties of Liquids cont'd
- Properties of Liquids cont'd
- Summary
- Sample Problem 1: Determine Which of the Following Liquids Will Have the Lower Vapor Pressure
- Sample Problem 2: Determine Which of the Following Liquids Will Have the Largest Standard Molar Enthalpy of Vaporization
- Intro 0:00
- Lesson Overview 0:10
- Introduction 0:46
- Intermolecular Forces (IMF)
- Intermolecular Forces of Polar Molecules 1:32
- Ion-dipole Forces
- Example: Salt Dissolved in Water
- Coulomb's Law & the Force of Attraction Between Ions and/or Dipoles
- IMF of Polar Molecules cont'd 4:36
- Enthalpy of Solvation or Enthalpy of Hydration
- IMF of Polar Molecules cont'd 6:01
- Dipole-dipole Forces
- IMF of Polar Molecules cont'd 7:22
- Hydrogen Bonding
- Example: Hydrogen Bonding of Water
- IMF of Nonpolar Molecules 9:37
- Dipole-induced Dipole Attraction
- IMF of Nonpolar Molecules cont'd 11:34
- Induced Dipole Attraction, London Dispersion Forces, or Vand der Waals Forces
- Polarizability
- IMF of Nonpolar Molecules cont'd 14:26
- Intermolecular Forces (IMF) and Polarizability
- Properties of Liquids 16:48
- Standard Molar Enthalpy of Vaporization
- Trends in Boiling Points of Representative Liquids: H₂O vs. H₂S
- Properties of Liquids cont'd 18:36
- Aliphatic Hydrocarbons
- Branched Hydrocarbons
- Properties of Liquids cont'd 22:10
- Vapor Pressure
- The Clausius-Clapeyron Equation
- Properties of Liquids cont'd 25:52
- Boiling Point
- Properties of Liquids cont'd 27:07
- Surface Tension
- Viscosity
- Summary 29:04
- Sample Problem 1: Determine Which of the Following Liquids Will Have the Lower Vapor Pressure 30:21
- Sample Problem 2: Determine Which of the Following Liquids Will Have the Largest Standard Molar Enthalpy of Vaporization 31:37
General Chemistry Online Course
I. Basic Concepts & Measurement of Chemistry | ||
---|---|---|
Basic Concepts of Chemistry | 16:26 | |
Tools in Quantitative Chemistry | 29:22 | |
II. Atoms, Molecules, and Ions | ||
Atoms, Molecules, and Ions | 52:18 | |
III. Chemical Reactions | ||
Chemical Reactions | 43:24 | |
Chemical Reactions II | 55:40 | |
IV. Stoichiometry | ||
Stoichiometry I | 42:10 | |
Stoichiometry II | 42:38 | |
V. Thermochemistry | ||
Energy & Chemical Reactions | 55:28 | |
VI. Quantum Theory of Atoms | ||
Structure of Atoms | 42:33 | |
VII. Electron Configurations and Periodicity | ||
Periodic Trends | 38:50 | |
VIII. Molecular Geometry & Bonding Theory | ||
Bonding & Molecular Structure | 52:39 | |
Advanced Bonding Theories | 1:11:41 | |
IX. Gases, Solids, & Liquids | ||
Gases | 35:06 | |
Intermolecular Forces & Liquids | 33:47 | |
The Chemistry of Solids | 25:13 | |
X. Solutions, Rates of Reaction, & Equilibrium | ||
Solutions & Their Behavior | 38:06 | |
Chemical Kinetics | 37:45 | |
Principles of Chemical Equilibrium | 34:09 | |
XI. Acids & Bases Chemistry | ||
Acid-Base Chemistry | 43:44 | |
Applications of Aqueous Equilibria | 55:26 | |
XII. Thermodynamics & Electrochemistry | ||
Entropy & Free Energy | 36:13 | |
Electrochemistry | 41:16 | |
XIII. Transition Elements & Coordination Compounds | ||
The Chemistry of The Transition Metals | 39:03 | |
XIV. Nuclear Chemistry | ||
Nuclear Chemistry | 16:39 |
Transcription: Intermolecular Forces & Liquids
Hi, welcome back to Educator.com.0000
Today's session in general chemistry is going to be concerning intermolecular forces and liquids.0002
As always we are going to start off with a brief introduction.0012
Then we are going to talk about the intermolecular forces first of polar compounds and finally of nonpolar compounds.0015
After we talk about the intermolecular forces in these classes of compounds, we will then0024
get into properties of liquids and how intermolecular forces affect these properties.0030
As always we will go ahead and do a brief summary of the presentation followed by some sample problems.0038
For the introduction, what we are looking at is basically the attractive forces that hold molecules together.0048
If you have a molecule and an identical molecule comes along right beside it,0056
what is responsible for those two molecules interacting with each other or attracting each other?0063
We call these forces of attraction intermolecular forces.0067
For my presentation, I am going to be abbreviating intermolecular forces as IMF.0073
What we are going to see is a good application of IMF.0080
We will see that the strength of a liquid's IMF can easily influence how it behaves physically.0085
Let's now get into the intermolecular forces for polar molecules.0092
The first type of IMF for polar molecules is what we call an ion-dipole force.0098
An ion-dipole force is going to occur between a polar molecule and an ionic compound.0104
For the example that I want to look at on the particulate level, this is going to be table salt dissolved in water.0111
Here I have water and table salt.0118
As soon as I dissolve table salt in water, the sodium chloride is going to break up into ions.0126
We have Na+ and Cl1-.0131
We have already discussed polarity previously.0136
We know that water is partial positive here, partial positive here, and partial negative there.0139
Something interesting is going to happen.0146
The partial negative end of oxygen is going to get attracted to the full positive ion that is sodium.0148
In addition, the partial positive end of water is going to get attracted to the full ion that is chloride.0160
This is what we call an ion-dipole force.0171
It is basically the attraction between an actual ion that has a full charge and a compound that has a dipole moment.0175
Coulomb's law describes the force of attraction between ions and/or dipoles.0188
Basically Coulomb's law tells us that this attraction is going to0194
be proportional to the following: q1q2 over r20200
where q1 and q2 are the relative charges of the cation and anion; charges of cation and anion.0210
r is just the distance between the two nuclei; ionic distance.0227
We see a very important proportionality.0237
That the force of attraction is going to be directly proportional to the magnitude of the charges.0242
It is going to be inversely proportional to 1 over r2 or inversely proportional to the atomic size.0254
Once again this is what we call Coulomb's law.0264
It tells us, it really quantifies the degree of attraction between charges and/or dipoles.0267
There is one important physical parameter that describes what we just illustrated.0280
That is an ion interacting with a solvent.0285
This is what we call the enthalpy of solvation which is also known as the enthalpy of hydration.0290
Basically what it is is the following.0299
It is another type of ΔH like we learned before.0302
It is also a ΔH of solvation.0307
It describes the energy change when an ion becomes solvated.0311
In other words, when an ion becomes surrounded by solvent molecules.0323
What we want to know, remember mother nature favors low energy.0336
The more negative this energy, the more likely an ion will be dissolved or solvated by water.0339
An ion is more likely to be solvated by water the larger it is and the more positive the charge.0346
Let's go ahead and move on then.0358
Ion-dipole was the first type of IMF for a polar compound.0364
Let's now move on to the second type.0369
The second type of IMF that can occur in liquids is what we call dipole-dipole forces.0372
Dipole-dipole forces occur between molecules that have a permanent dipole moment.0379
Then the strength of the dipole-dipole force tends to increase with overall polarity.0386
For example, if we take a carbon-hydrogen bond versus an OH bond,0391
the OH bond is the more polar of the two and therefore will have a stronger IMF.0397
How does this all relate to boiling point?0411
Basically the stronger the IMF, the more energy required to overcome the attraction.0415
When we think of energy, we can think of boiling point.0421
Boiling point is the temperature at which the boiling process is going to occur.0425
Remember temperature is the measure of average kinetic energy.0428
Really when we say the more energy required to overcome the attraction, we really mean a higher boiling point.0432
This was again dipole-dipole forces.0442
The next type of intermolecular force is what we call hydrogen bonding.0445
Hydrogen bonding you can think of as a very strong type of dipole-dipole.0450
This is going to occur in a molecule that has hydrogen that is directly bonded to nitrogen, oxygen, or fluorine.0454
You will recognize these three elements being the most electronegative.0462
Therefore their bond with hydrogen will be the most polar.0467
Hydrogen bonding is important of course biologically because we are going to find out that liquids that0474
have hydrogen bonding tend to be number one, nonvolatile, and number two, have relatively higher boiling points.0480
You can think of water as our typical example.0487
Hydrogen here, partial positive, partial positive, partial negative.0493
We can have another water molecule come into play just right there.0497
We can have an interaction between the partial negative oxygen with the partial positive oxygen.0502
You can imagine another water molecule just like that; we can have even more attraction.0508
What we see is basically that we get a network of hydrogen bonding; network of strong hydrogen bonding.0520
Why is this biologically important?0537
We know water because of its strong hydrogen bonding is going to be nonvolatile.0539
Imagine if all the world's oceans all of a sudden evaporated.0546
Life would be unbearable; our planet would be too hot.0551
Because of hydrogen bonding, water does not evaporate.0554
That allows us to have a good cooling effect by the ocean.0557
Again that is also going to lead to a high boiling point.0563
Once again it is in our best interest to have water to be a very stable compound.0568
Again it is due to hydrogen bonding.0575
What we are going to go into now, now that we are done with polar molecules,0579
let's get into the intermolecular forces for nonpolar molecules.0583
We are first going to look at the solubility of a nonpolar gas in a polar solvent.0588
Wait a second, I thought polar and nonpolar are not supposed to mix.0596
But it turns out that for gases, there can be a slight degree of mixing.0599
The typical example is going to be carbon dioxide in water which is basically your average carbonated beverage like soda.0605
We all know that CO2 is nonpolar.0614
Let's go ahead and look at its Lewis structure.0619
Each oxygen is partial negative; the carbon is partial positive.0623
What can happen is the following.0629
A water molecule can come into play right here just like that.0632
Partial positive, partial positive, and partial negative.0641
Even though carbon dioxide is nonpolar, at any one point in time, at any point in time,0646
an electron cloud can get slightly distorted; electron density can distort.0660
As soon as we get a distortion, that instant we form a temporary dipole moment.0672
It is that temporary dipole moment which can then interact with the polar water molecule.0685
Let's go ahead and take a look at the interaction between two nonpolar molecules.0698
The interaction between two nonpolar molecules is what we call a London dispersion force or a van der Waals force.0703
Another name for it is induced dipole attraction.0712
Let's go ahead and take a look at molecular fluorine as an example.0716
Here is our typical Lewis structure for a molecular fluorine.0722
Because it is homonuclear diatomic, it is nonpolar overall.0726
However, at any point in time, we can have distortion of the electron cloud once again; distortion of electron density.0730
You can imagine then that at any one point in time, if what I am drawing represents the F2 molecule,0746
we can get one side to be partial positive and we can get one side to be partial negative.0754
This is not going to last forever.0760
It is a temporary dipole moment just like it was for carbon dioxide.0761
Basically if I have this temporary dipole moment, another F2 molecule can come into play, can come right alongside it.0770
It too can also have a temporary dipole moment.0781
We can get an interaction between the partial positive end of one F20784
molecule with the partial negative end of the second F2 molecule.0789
Because of the temporary nature though of this interaction, we can also0794
infer that London dispersion forces are going to be incredibly weak.0799
In fact, dispersion forces are the weakest type of intermolecular force due to temporary nature of attraction.0806
This brings into play a very important concept.0829
You are going to see this concept in this chapter.0832
You are going to see this concept in organic chemistry quite a bit actually when you get to that level.0835
To what extent does an electron cloud or electron density get distorted?0841
The extents to which this happen is known as polarizability.0848
Basically the more polarizable the molecule, the easier it is to0854
have an induced dipole moment and therefore the stronger this attractive force.0860
Let's go ahead and look at the molecular halogens as our example.0866
F2, CL2, Br2, and I2.0873
Under standard conditions, fluorine is a gas; chlorine is a gas.0880
Bromine is a liquid; I2 is a solid.0885
Why is that though?--why are we going from gas to liquid to solid?0890
In other words, as we go down this column, why does the intermolecular forces increase?0894
Because that is what explains for going to a more condensed state from gas to liquid to solid.0906
Why does the IMF increase?--the answer is because of polarizability.0911
Iodine is the largest out of these molecules.0921
Because it is the largest, the electrons are not held as tightly.0927
Because the electrons are not held as tightly, we get easier distortion.0939
More likely for electron cloud distortion to occur.0945
Because it is more likely for the electron cloud distortion to occur, we can form stronger dispersion forces.0955
In other words, polarizability increases with molar mass.0976
Once again polarizability tends to increase with molar mass; that is it.0991
That pretty much explains why we change physical state as you go down the column of0997
the halogens from fluorine to iodine, from a gas all the way to a solid.1003
We finished our discussion on the attractive forces that can occur for liquids.1012
Let's go ahead and apply them now.1019
We are going to apply these to the physical properties of liquids.1021
There are several of them.1026
The first physical property that we are going to be talking about is what we call standard molar enthalpy of vaporization.1027
It is yet another energy; it is another type of enthalpy.1034
The definition of ΔH of vaporization is the energy required to vaporize one mole of a liquid under standard conditions.1038
But in order to vaporize a liquid, you have to overcome the intermolecular forces,1046
the IMF whether it be dipole-dipole, hydrogen bonding, or dispersion.1051
In other words, the stronger a liquid's IMF, the more energy required and the larger the ΔH of vaporization.1056
Let's go ahead and look at the trends and boiling points of representative liquids.1064
Here we will examine two inorganic liquids, water and hydrogen sulfide.1069
For water, let's look at the IMF; we have hydrogen bonding here.1075
For hydrogen sulfide, there is no hydrogen bonding; only dipole-dipole and van der Waals.1080
Because hydrogen bonding is going to be the strongest type of intermolecular force here,1089
we conclude that water has the stronger IMF and therefore the higher ΔH of vaporization.1094
That is how we apply intermolecular forces to solving these types of problems.1110
Let's go ahead and take a look at some representative organic liquids.1118
The first type of organic liquids I want to talk about are what we call aliphatic hydrocarbons.1122
Aliphatic hydrocarbons are basically straight-chain alkanes.1126
Here we have CH3CH2CH3 and CH3CH2CH2CH3.1131
First of all, if you recall the electronegativities of carbon and hydrogen are very similar.1137
In fact, they are nonpolar bonds; both of these molecules are nonpolar.1142
Because both of these are nonpolar, the only type of intermolecular force are van der Waals in each of them.1149
What is the only difference then?--the only difference is chain length or molar mass.1156
We see here that this has the longer chain which means higher molar mass.1162
Just like we said previously, as the molar mass increases, the polarizability1171
also tends to increase, therefore the strength of the intermolecular force.1176
Therefore this molecule here, CH3CH2CH2CH3, has the stronger IMF1180
because of intermolecular forces... excuse me... of the higher molar mass and stronger IMF.1186
The next two, CH3CH2OH versus CH3OCH3.1197
In this left molecule, we have hydrogen bonding and dipole-dipole.1202
In the right molecule, there is no hydrogen bonding; only dipole-dipole and van der Waals.1210
We are going to obviously pick the one with the hydrogen bonding.1221
That is going to give us the stronger IMF and therefore the higher ΔH of vaporization.1224
These are again just examples of what we call aliphatic hydrocarbons, straight-chain alkanes.1247
We now move on to branched out hydrocarbons.1252
For branched hydrocarbons, it is important to go ahead and draw the Lewis structures out.1257
This one we did already, CH3CH2CH2CH3.1263
Nothing is going on here; this is aliphatic.1268
But when we move to its counterpart on the right side, we are1271
going to get a new type of structure that looks like this.1275
This is what we call a branched alkane; this is no longer aliphatic.1283
What we have to take away from this is the following.1290
That any type of branching is going to lower the surface area of your compound.1292
If the surface area is lower, that means there is less area of the molecule to be exposed to an adjacent molecule.1304
In other words, the IMF is going to be lower also.1314
This molecule here that is branched has the weaker IMF and therefore the lower ΔH of vaporization.1320
Next another physical property is what we call vapor pressure.1331
Vapor pressure is going to be commonly measured in our traditional units1337
for a gas pressure which is atm, torr, and even kilopascal.1341
What vapor pressure is is the following.1347
It is going to be the pressure of a vapor that is directly above the surface of its liquid in dynamic equilibrium.1349
If you take a small beaker and you cover the beaker and you close it, let's say you have a liquid in here.1358
That liquid is going to go into a gas phase naturally.1368
But not all of it because as soon as the gas forms, it is going to go back and condense back down to a liquid.1375
This is in constant motion and not a static condition.1381
This is what we call dynamic equilibrium; it is a dynamic process.1387
Basically whenever we have this type of closed system, if we measure the pressure of1393
the vapor right above the liquid, that is what we call vapor pressure.1399
Now that we have a little drawing to help support the idea of vapor pressure, we can now put it into play.1408
Vapor pressure is actually going to parallel what you and I know as smell.1415
Basically a liquid with a strong odor, we are detecting its gas phase with our nose.1421
A liquid with strong odor means it vaporizes easily.1427
Its vapor pressure is going to be relatively high.1430
If you compare gasoline versus water, gasoline we know smells very strongly.1433
Water has no odor; we can conclude that gasoline has a higher vapor pressure.1445
The technical term for this with a higher vapor pressure is what we call volatile; volatile.1456
We say water is therefore is nonvolatile.1463
We do have an equation that allows us to quantify the relationship between vapor pressure and temperature.1473
This is what we call the Clausius-Clapeyron equation.1484
The Clausius-Clapeyron equation is basically the natural log of P2 over P1 which is equal to...1488
ΔH of vaporization over R times 1 over T1 minus 1 over T2.1507
All this is saying is the following.1515
If T2 is greater than T1, that automatically implies that P2 is greater than P1.1519
In other words, vapor pressure increases with temperature; P increases with temperature.1527
Just think about that.1535
A gas station is going to smell a lot worse on a warmer day.1537
It is because the vapor pressure of any gasoline that is dropped is going to be much higher than on a cooler day.1541
That is again the Clausius-Clapeyron equation.1550
The next physical property of liquids is what we call normal boiling point.1553
Normal boiling, we all know what boiling point is.1557
It is the temperature at which a liquid is going to boil.1560
But normal boiling point is specifically the process that occurs at atmospheric pressure.1562
Since boiling requires energy, a high boiling point implies that lots of energy is needed to boil a liquid.1569
A high boiling point means very strong IMF which also means1577
higher ΔH of vaporization which also means lower vapor pressure.1588
Let me go ahead and summarize that.1601
Strong IMF, high boiling point, high ΔH of vaporization, lower vapor pressure.1603
Simply knowing the intermolecular force, we can take an educated guess at a lot of the physical properties of a liquid.1618
Now onto the last physical properties we will cover.1630
This one is what we call surface tension.1634
Surface tension is something measurable.1636
It basically quantifies the tendency of a liquid to minimize its surface area.1639
To do this, it is going to form spherical drops.1644
A liquid with a relatively high surface tension easily forms spherical droplets1649
such as water which has very strong IMF due to hydrogen bonding.1655
Liquids with low surface tension, they tend not to form spherical droplets; nonspherical droplets.1663
Finally we reached the last physical parameter of liquids.1686
It is what we call viscosity; viscosity is also measurable.1693
It basically quantifies a liquid's resistance to flow.1698
What that really translates to is how thick a liquid is.1702
If you think of something like honey or like syrup, we say those are very viscous liquids.1706
They are very resistant to flow.1712
Basically if an IMF is very large, the viscosity tends to also be large.1714
That makes sense that the intermolecular force of attraction is large.1720
Liquid is not going to want to separate from each other.1724
It is going to want to stay intact and stay together.1726
In other words, it is going to be somewhat thick if you will or not as flow-like as water or something like that.1728
Again this is what we call viscosity.1741
We now reach our summary slide.1746
Basically in this chapter, we introduced the types of intermolecular forces that are relevant to liquids.1750
Number one is what we call ion-induced dipole; number two is what we call dispersion.1757
Number three is what we call dipole-dipole; number four is what we call hydrogen bonding.1762
Remember ion-induced dipole is going to be between a free ion and a polar molecule.1768
Dispersion is going to occur between nonpolar compounds.1780
Dipole-dipole and hydrogen bonding are going to be for polar compounds.1784
After we went over all of the different types of intermolecular forces, we then applied them1791
and used them to make educated guesses on how a molecule is going to behave physically.1796
We saw that the IMF can exert strong influence on a liquid's physical properties such as boiling point and vapor pressure.1803
In other words, by using IMFs, we can make a strong educated guess on the relative volatility of a liquid.1813
For sample problem one, let's go ahead and determine which of the following liquids will have the lower vapor pressure.1823
As soon as I see this molecule here which is OH, I see hydrogen bonding immediately.1830
That tells me this molecule is going to have relatively strong intermolecular forces.1836
Here CH3OCH3, that is going to look a lot like this.1841
I don't have any hydrogen bonding at all.1847
But I do have dipole-dipole and of course van der Waals or dispersion.1849
For here, CH3CH2CH3, there is none of that.1858
There is no dipole-dipole; there is no hydrogen bonding.1864
This molecule is completely nonpolar.1867
I am only left with van der Waals or dispersion.1871
What low vapor pressure means is that we are going to have strong intermolecular forces.1878
Therefore the molecule that is expected to have the lower vapor pressure is going to have the strongest intermolecular forces.1886
That is the CH3CH2OH right there.1893
Finally sample problem two, we are going to take the same compounds.1899
But now we are going to determine which of the following will have the largest ΔH of vaporization.1903
As soon as I see largest ΔH of vaporization, that means a lot of1912
energy is required to vaporize one mole of a liquid under standard conditions.1916
That tells me I am dealing with a liquid with relatively strong IMF.1920
Using the same rationale, it is going to be the CH3CH2OH again expected1927
to have the largest ΔH of vaporization because this has hydrogen bonding.1931
This one in the middle has only really dipole-dipole and dispersion.1938
This one here has only dispersion.1946
What I encourage you to do is when you tackle these types of problems,1951
you should always try to from the formula get the structure, the Lewis structure that is,1955
because that will really help you see any of types of bonds.1963
Step two is then go ahead and identify the types of IMF present.1966
Hopefully that is enough to distinguish the liquids from each other.1979
But if IMF identical, then what you need to go by is really1984
the size of the molecule or its molar mass; go by molar mass.1993
Again what was the word that describes the effect of molar mass and size on distortion of electron cloud?1999
This is all related to polarizability; good.2006
That was our general chemistry lecture on intermolecular forces and liquids.2015
I want to thank you guys for your attention.2021
I will see you next time on Educator.com.2024
1 answer
Tue Apr 7, 2015 11:57 PM
Post by Akilah Miller on April 7, 2015
Hello Professor,
I am a bit confused: on slide 5 you say that r represents the atomic size but does it not represent the distance between the the molecule and/or atoms that interact with each other?
1 answer
Sun Feb 15, 2015 11:44 PM
Post by Anthony Linares on February 9, 2015
Greetings. am new to educator.com and I was just wondering why the video is not working.
1 answer
Tue Oct 14, 2014 6:55 PM
Post by Luisa Gualtieri on October 13, 2014
So for long alkane chains, it is the incrase in molar mass that has the greater effect on boiling point, and not the length of the chain making an increased separation and stretching it thin in terms of dipole-dipole interaction between nuclei. Am I correct?
1 answer
Wed May 7, 2014 6:46 PM
Post by Heather Marck on May 7, 2014
How could you tell so quickly that H2S had dipole-dipole and V.d.W?