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TL;DR: The $\ce{O-O}$ and $\ce{S-S}$ bonds, such as those in $\ce{O2^2-}$ and $\ce{S2^2-}$, are derived from $\sigma$-type overlap. However, because the $\pi$ and $\pi^*$ MOs are also filled, the $\pi$-type overlap also affects the strength of the bond, although the bond order is unaffected. Bond strengths normally decrease down the group due to poorer $\...


32

The boiling point of a liquid depends on the intermolecular forces present between the atoms or molecules in the liquid since you must disrupt those forces to change from a liquid to a gas. The stronger the intermolecular forces, the higher the boiling point. Two oxygen molecules are attracted to each other through London dispersion forces (induced ...


32

I quote the Green Book by IUPAC, 2nd printing (2008), section 1.6, enumeration item 2: The overall rule is that symbols representing physical quantities or variables are italic, but symbols representing units, mathematical constants, or labels, are roman. [...] As such, the correct way to write it is $\ce{NO}_x$, because $x$ is a variable. Please note ...


29

Table salt! What would be worse than putting sodium (it can spontaneously combust if you get it wet) and chlorine (used as a war gas in WWI) all over your food? Then there's water which always contains some $\rm OH^-$ (an active ingredient in Drano) and $\rm H^+$ (that stuff eats through metal, man). Although those aren't elements. And hiding inside every ...


26

There's an interesting article here - Illustrating Atoms and Molecules - that discusses atom colors: In 1865, the chemist August Hoffman gave a Friday Evening Discourse at London’s Royal Institution on the “Combining Power of Atoms.” In order to demonstrate chemical bonding of atoms, he drilled holes in croquet balls and connected them with metal pipes (...


25

Simply speaking, because it's an appropriate unit to use. Let's imagine I wanted to measure the length of a rope. What would be an appropriate length to use? Inches? Centimeters? Feet, maybe? It would really be awkward to express it as 0.000189393 miles, or as 304,800,000 nanometers. (Note: if you can't see why these units are awkward, take any page ...


25

Diamond is a covalent network solid, like a number of other common materials (quartz, graphite, glass, and a whole bunch of stuff). Because they are not discrete molecules - there is no 'diamond' molecule the same way there are molecules of caffeine, benzoic acid, citric acid, N,N-dimethylaminopyridine, etc. - network solids form one of the two main classes ...


25

The visible fog that forms when liquid nitrogen is poured into an open container is almost entirely water fog: the boiling nitrogen chills the air above it, causing the humidity in the air to condense into fog. There may be some microdroplets of liquid nitrogen in the fog too, but the air, even after it's been chilled, is still much warmer than the boiling ...


23

Yes, they are possible; several have even been detected. They all have the general formula $\ce{H2O_{n}}$ and belong to the class of hydrogen polyoxides. Of course, the $n=1$ member of the series is water $(\ce{H2O})$, and the $n=2$ member is hydrogen peroxide $(\ce{H2O2})$. The $n=3$ member is trioxidane $(\ce{H2O3})$, and it has the following structure:...


22

Noble gases usually do not form strong bonds between their atoms - it takes fair amount of energy to dimerise them into excimers, but those are short-lived excited molecules. Thanks to excitation, shells of the atoms aren't closed and they react, but very quickly they lose energy and become separate atoms. On the other hand there are many stable molecules ...


21

In short: the definition of a chemical bond is not unique and a clearly-drawn line. The simplest and most common definition is the sharing of electrons between two or more nuclei. In contrast, other interactions are often said to be intermolecular (which is somewhat more specific than the term “physical”. In a longer commentary, I see can have five ...


20

$\ce{H_{2}O}$ is the water molecule, two hydrogen atoms attached to a central oxygen atom, $\mathrm{C}_{2v}$ symmetry, thermodynamically minimal structure of these atoms, Adam's ale, etc. HHO is a poorly defined term often bandied around by 'water powered car'... enthusiasts. I'm not sure that it's supposed to represent a molecule so much as a state of ...


18

There are 3 types of octet rule "violations" or exceptions molecules with an odd number of electrons, such as nitric oxide (image source) molecules with less than 8 electrons around an atom, $\ce{BeCl2}$ and $\ce{BH3}$ serve as examples (image source) molecules with more than 8 electrons around an atom, such as $\ce{PCl5}$ or $\ce{SF6}$ Take a look at ...


18

According to the website, Open Babel should do the trick: Documentation - SMILES, Sourceforge. For example, the following code will give you a neat SVG file of the molecule benzene: obabel -:"c1ccccc1" -O benzen.svg If you experience problems using it, you are welcome to ask more specifically. Alternatively, you can use a web-query from the national ...


17

Chemical reactions occur because the thermal energy in a substance makes molecules bump into each other, and each time they bump into each other there is some chance for a reaction to take place. This is an oversimplified model, but it suffices to get some intuition for what's going on. The molecules of course do not "know" that some configuration is more ...


17

I've done some work in both symmetry detection and in distance matrix methods. I think it's a great idea in concept, but the devil will be in the details for large, more complex molecules. The first problem is that distance geometry methods are over-determined. For each atom, there are range constraints to the other $N-1$ atoms (a lower bounds and an upper ...


17

It appears that symmetric hydrogen bonds can exist between neutral molecules, even between water molecules! But it takes 60 GPa of pressure to make water to bond like that. Article named very descriptively "Compression of Ice to 210 gigapascals: Infrared Evidence for a Symmetric Hydrogen-Bonded Phase" proves it: Protonated and deuterated ices ($\ce{H2O}$ ...


16

15 is there because you have 5 atoms which can move independently, and we live in a 3D space, and $3\ \times\ 5\ =\ 15$. 3 of these are translational degrees of freedom, which you seem to agree with, so I'll just leave it at that. 3 are for rotations, because the methane molecule is not linear. Axes of symmetry are irrelevant: indeed, you may rotate ...


15

A lot of non-systematic chemical names don't describe the composition of the compound, they describe what the compound is synthesised from. That is the case here since EDTA is derived from ethylene by adding two units of the diamine. It isn't that uncommon in chemical names. Polyethylene, for example, is (simplifying only slightly) a long chain of carbons ...


15

Why can't fluorine be the central atom in inter-halogen compounds? First off, fluorine can be at the "center of things." Examples would include the strongly hydrogen bonded hydrofluoric acid and the very relevant example of the trifluoride anion $$\ce{[F-F-F]^-}$$ The trifluoride anion example is critical as it demonstrates that fluorine can be ...


15

It is all about minimizing the energy of a molecule. In the case of carbon, the only molecule that adopts a perfect hexagonal geometry in its ground state is benzene (and its derivatives that possess a 6-fold rotational axis). In this case the hexagonal geometry is adopted because all of the carbons are $\ce{sp^2}$ hybridized. The ideal geometry (lowest ...


15

This question crossed my mind during a lab today because we were making $\ce{Ni(dmg)2}$, which is shown below. Well first, this is charged in some sense, but it is net-neutral. Also, the configuration shown above is only one way to draw it, and it seems as if everything should be symmetrical and thus that hydrogen should be equally shared between the two ...


14

You need to mix the orbitals, populate them with the electrons and see if you have net bonding. Eg: H + H two 1s orbitals mix to form sigma and sigma*. Two electrons total, both occupy the sigma orbital, two more electrons in bonding than antibonding orbitals, the compound is stable. Eg: He + He; same mixing as above. Four electrons, two in the sigma, ...


14

You have drawn the compounds correctly, and yes a solid wedge means the bond is coming out of the plane of the screen towards you a dashed wedge means the bond is going behind the plane of the screen away from you a solid line means the bond lies in the plane of the screen Here is a Newman projection of your molecules, sometimes Newman projections can ...


14

Let me see if I can get at some of your questions. As mentioned above, it's much easier when you ask individual specific questions. One problem with books on introductory quantum mechanics is that, put simply, the language of quantum mechanics is math. Specifically, most people use the Schrödinger equation which involves second derivatives and differential ...


14

In non-nuclear chemistry, everything is electrostatic interactions. This is why you can learn and predict so much just by "following the electrons" Covalent bonds are also formed because of electrostatic interactions - they are just more complicated conceptually than ionic (actually, ionic bonds are more accurately described by wavefunctions, we just try to ...


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 ...


14

Atomic mass refers to the average mass of an atom. This has dimensions of mass, so you can express this in terms of daltons, grams, kilograms, pounds (if you really wanted to), or any other unit of mass. Anyway, as you said, this is an average of the masses of the isotopes, weighted by their relative abundance. For example, the atomic mass of $\ce{O}$ is $15....


13

Clearly, molecules are not in any sense volitional agents. They're simply subject to the basic and immutable laws of thermodynamics, the second of which states that any isolated system always spontaneously develops toward a state of equilibrium in which entropy (which can be informally described as "disorder" or "randomness," meaning thermal energy ...


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