46
Yep, it has to do with the orbitals.
$\ce{CO2}$ is linear, so even though the $\ce{C-O}$ bonds have individual dipole moments, the overall dipole moment is zero as these cancel out (they point in opposite directions, as shown in the diagram below).
On the other hand, $\ce{H2O}$ is "bent", which means that the individual dipole moments of the bond are at an ...
27
Mini Research Project Time
Updates
Added CCSD(T) $n_i$ and dipole moments and tweaked discussion (the delay was caused by a system-wide storage upgrade on the machines which took nearly a week to complete).
Preamble
This response is in no way meant to be contrary to what Geoff has already posted. I happen to enjoy these types of questions and I like to ...
20
To directly address where the phrase comes from:
Water is called the "universal solvent" because it dissolves more substances than any other liquid. -USGS
What are ideal qualities of solvent?
The strength of a solvent can be attributed to the strength of its intermolecular forces like london forces, dipole-dipole forces, ion-induced dipole, and hydrogen ...
20
TL;DR: Water is incredibly easy to get and work with.
In full
Water is a good solvent for polar compounds[citation needed], and the reasons for this are laid out pretty well by John Snow, but that's not really what makes it the universal solvent.
Instead, a series of other, incidental properties makes it a popular choice:
Availability
There's a lot of ...
16
so wouldn't it be that you
would have an even more positive carbon and 2 partially negative
oxygens
Yes, your analysis is correct to this point. A chemist would say that the bonds in $\ce{CO2}$ are polar (or polarized) and therefor each $\ce{C=O}$ bond has a bond dipole moment. However the molecule itself is linear and the two bond dipole moments are ...
16
Just to provide an alternative answer:
Consider a solvent miscibility table like the one linked.
What is the least miscibile solvent? Water! Water is the worst solvent. Water is immiscible with 17 out of 30 of the other listed solvents.
There are 6 solvents in the table which are miscible with all the other solvents: ethanol, acetone, tetrahydrofuran, n-...
14
Draw the structures in 3D and then you will see why one is polar and the other not.
$\ce{CF4}$:
As you can see this molecules adopts a tetrahedral geometry which is perfectly symmetrical in every direction and so the dipoles of the four $\ce{C-F}$ bonds cancel out, leaving no overall dipole.
$\ce{CHF3}$:
Although the molecule has some symmetries, it is ...
13
The structure of the triiodide ion places a negative formal charge on the central iodine atom.
No it doesn’t. The two resonance structures that describe the four-electron three-centre bond put the negative formal charge on the outer iodines ($\ce{1/2-}$ each).
That said, polarity is usually defined as having a non-zero dipole moment. The dipole moment’s ...
13
What is a quadrupole moment of a molecule and how does it arise?
This explanation is geared at someone with one year of chemistry. It captures the gist but is not rigorous:
To test for monopoles, dipoles or quadrupoles in a molecule or ion, assign charges or partial charges to each atoms. For partial charges, δ+ and δ- is fine (if you want estimated values ...
13
Because it takes two to tango.
Dipoles interact with each other. A Lone dipole has nothing to interact with (other than an electric field, but if we ignore some externally applied macro field, there is nothing for a lone dipole to interact with).
So molecules with an inherent dipole (like water or chloroform) interact with each other. One molecule's dipole ...
12
If you're looking at the overall polarity of the solvent, you're not only consider the value of the individual dipole moment on a single molecule, but also their “density”, i.e. the number of these dipoles per unit of volume. You are right that the dipole moment of an individual linear-chain alcohol will, in first approximation, be independent of the chain ...
12
This was actually an interesting problem.
Well, I ran a quick calculation using Avogadro and GAMESS, although other packages would work. This is a CCSD/aug-cc-pVTZ calculation, pretty much the gold standard in quantum chemistry. (CCSD(T) and a larger basis set might be better, but are unlikely to differ much here and I can't run them on my laptop.)
The ...
12
Very simply, you explain the reason for this solubility rule by taking in consideration the energy requirements for the breaking of intermolecular forces between the molecules in the solute and the solvent.
Note: this is only a simplified explanation as it also depends on other factors such as change in entropy
Here is some background information on ...
11
According to this paper:
Planar configurations for resorcinol and hydroquinone are more acceptable on comparison of experiment and calculation than are the structures assuming either free or partially restricted rotation of the hydroxyl groups.
It states that the dipole is present because there is restricted rotation with the hydroxyl groups. The ...
11
I would argue it is a polar molecular ion.‡ In the comments to this question there has been already pointed out that the term "polarity" is quite ill-defined.
Many chemists understand that if a molecule has a vanishing dipole moment, the molecule itself is non-polar; at least this is true since molecules are neutral by definition. If you actually can ...
11
If you accept the Atkins Physical Chemistry definition of polar:
A polar molecule has a permanent electric dipole moment arising from the partial charges on its atoms
Then the answer turns upon whether triiodide is actually linear.
Isolated Triiodide and Pentaiodide Anions in the Crystal Structure of [Rb(Dibenzopyridino-18-Crown-6)2]2(I3)(I5) ...
11
As the other answers have indicated, CO2 has no NET dipole moment. However it does have two dipoles pointed in opposite directions (as OP keeps mentioning). This means that CO2 can possibly interact through higher moments, such as the quadrupole moment. The mathematical procedure behind this is known as the multipole expansion. It is important to note ...
10
In understanding molecular polarity you need to take the whole structure into account.
Your reasoning is correct as far as the parts of the molecule are concerned. The individual bonds are polar.
But, a molecule can only be polar if it has a net dipole moment (that is, the charges don't balance out in direction across the whole molecule). So CO is polar as ...
10
Taken from my answer to your original question
There are a couple of reasons why $\ce{CO2}$ is more soluble in water than $\ce{O2}$. Because the two $\ce{C=O}$ bonds in $\ce{CO2}$ are polarized (whereas in $\ce{O2}$ the bond is not polarized) it makes it easier for the polar water molecule to solvate it and to form hydrogen bonds. Both of these factors ...
10
It's worth noting some of the history behind the term "universal solvent," and why it is used even though water isn't truly universal or even necessarily the most versatile solvent available.
Before chemistry existed, and for that matter before science existed as the practice we would recognize today, alchemy was an important protoscience. A number of ...
9
Just to add some quantification to Ben Norris's answer. Consider each $\ce{C-Cl}$ bond, which has a bond dipole moment of magnitude $A$. The contribution from $\ce{C-H}$ is neglected here to simplify the calculations.
Now consider dichloromethane. The resultant of the two $\ce{C-Cl}$ dipoles will have a magnitude of $$2A\cos\frac\theta2$$
where $\theta\...
9
The formula for the net dipole moment $\vec{\mu_{net}}$ of an overall neutral system of $n$ charged point particles is given by:
$$
\vec{\mu_{net}} = \sum\limits_{i}^{n} q_i\vec{r_i}
$$
where $q_i$ is the charge of the $i$th point particle and $\vec{r_i}$ is the position vector for said particle; each individual dipole moment points from a negative charge ...
9
Carbonates
The quote from your text:
Carbonates of alkaline earth
metals are insoluble in water and can be
precipitated by addition of a sodium or
ammonium carbonate solution to a solution
of a soluble salt of these metals. The solubility
of carbonates in water decreases as the atomic
number of the metal ion increases. All the
carbonates ...
9
TL;DR
It's because the enthalpy changes of a solution generally don't favor dissolution.
A longer version:
To explain this, usually the enthalpy change explanation is given. For the sake of understandability, let's see what happens when two compounds dissolve. Take ethanol dissolving in water as an example. Here's the gist of what happens:
The ...
9
I wish we would stop teaching chromatography in terms of "polar" and "nonpolar."
The aspirin will interact fairly strongly with the silica due to hydrogen bonding/electrostatic interactions of the carboxylic acid and the ester with the silica. If you increased the "polar" component of the mobile phase, it would travel further due to the mobile phase ...
9
Carbon dioxide is more than linear. It's symmetric, and the axis of symmetry perpendicular to the bonds also applies to whatever dipole moment it has. The only vector that looks the same after being rotated 180 degrees is the null vector, so the molecule has zero overall dipole moment.
Therefore, dipole-dipole interactions are not possible because carbon ...
9
After the successful calulation of the electrostatic surface potential, molden equally allows the display of it in a form like
(source)
A step-by-step, hopefully still functional, tutorial is this. (My last contact with Molden already dates back some years.)
8
Once you move up to "larger" molecules like this, the definition of a "polar" molecule becomes a bit fuzzy. Rather, you will find that molecules contain polar and non-polar groups which all contribute to the overall characteristics of the molecule. It really depends on the context that you are interested in.
If you are curious about more macroscale ...
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