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Why is gold golden?
130 votes

See the footnotes I've included if you would like to see more of the detail behind a specific statement. The figure below compares the reflectance spectrum for silver and gold (let's forget about ...

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How do you melt metals with super high melting points?
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87 votes

Tungsten's melting point of 3422 °C is the highest of all metals and second only to carbon (3550 °C) among the elements. This is why tungsten is used in rocket nozzles and reactor linings. There are ...

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Why does F replace the axial bond in PCl5?
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72 votes

Recently, there has been a lot of discussion of Bent's rule (see for example "What is Bent's rule?") here in SE Chem. Simply stated, the rule suggests that $\mathrm{p}$-character tends to ...

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What is Bent's rule?
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60 votes

That's a good, concise statement of Bent's rule. Of course we could have just as correctly said that p character tends to concentrate in orbitals directed at electronegative elements. We'll use this ...

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Are diamonds really forever?
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48 votes

how long would it take for this super-material to convert to the stuff I scribble with? No, despite the fact that James Bond said "Diamonds are Forever", that is not exactly the case. Although Bond'...

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Why do we write NH3?
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45 votes

According to current nomenclature rules, $\ce{H3N}$ would be correct and acceptable. However some chemical formulas, like $\ce{NH3}$ for ammonia, that were in use long before the rules came out, are ...

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What are the meanings of dotted and wavy lines in structural formulas?
42 votes

I was wondering what the wavy and the dotted line represent? A dashed line indicates that the bond is extending behind the plane of the drawing surface A bold-wedged line indicates that the bond is ...

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Why does bond angle decrease in the order H2O, H2S, H2Se?
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42 votes

Here are the $\ce{H-X-H}$ bond angles and the $\ce{H-X}$ bond lengths: \begin{array}{lcc} \text{molecule} & \text{bond angle}/^\circ & \text{bond length}/\pu{pm}\\ \hline \ce{H2O} & 104.5 &...

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Why is the bond angle H-P-H smaller than H-N-H?
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40 votes

Starting point: 2s orbitals are lower in energy than 2p orbitals. The $\ce{H-N-H}$ bond angle in ammonia is around 107 degrees. Therefore, the nitrogen atom in ammonia is roughly $\ce{sp^3}$ ...

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Carbon atoms at the edge of a diamond
37 votes

Atoms at the edge of a crystal that have an unsatisfied valence are said to have "dangling bonds." Many elements, in addition to carbon, can have dangling bonds. Dangling bonds is a subject of ...

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Why does basicity of group 15 hydrides decrease down the group?
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36 votes

Each of these molecules has a pair of electrons in an orbital - this is termed a "lone pair" of electrons. It is the lone pair of electrons that makes these molecules nucleophilic or basic. As you ...

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Inductive effect of hydrogen isotopes
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35 votes

Yes, it has a lot to do with mass. Since deuterium has a higher mass than protium, simple Bohr theory tells us that the deuterium 1s electron will have a smaller orbital radius than the 1s electron ...

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Is there any chemical that can destroy PTFE or Teflon?
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33 votes

Just to add a bit to Ben's excellent answer... A number of fluorinating agents also react with PTFE, $\ce{XeF2}$ and $\ce{CoF3}$ being examples Ben mentioned the reaction of magnesium metal. ...

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Thermodynamic vs Kinetic Sulphonation of Naphthalene
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33 votes

In contrast to many other electrophilic aromatic substitution reactions, aromatic sulfonation is reversible, in other words it is an equilibrium. If you use a large excess of $\ce{SO3}$ you push the ...

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Is buckminsterfullerene aromatic?
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33 votes

Aromaticity is not binary, but rather there are degrees of aromaticity. The degree of aromaticity in benzene is large, whereas the spiro-aromaticity in [4.4]nonatetraene is relatively small. The ...

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Hypothetical: What happens to water as pressure increases to infinity?
32 votes

The phase diagram for water (reported in your link and reproduced below) is a good starting point. The diagram shows us that at pressures around 1 terapascal (about 10 million atmospheres) ice is a ...

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Is pyrene aromatic despite failing Hückel's rule?
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31 votes

Pyrene is aromatic. The Hückel $4n+2$ rule works best with monocyclic ring systems. If you look at the following resonance structure for pyrene with a central double bond, the monocyclic periphery has ...

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Relative stability of cis and trans cycloalkenes
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31 votes

Usually trans-olefins are more stable than their cis isomers for steric reasons, like you suggested. However in small and medium size rings this is not the case; here the cis-cycloalkene is more ...

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Is the ammonium substituent (-NH3+) really meta-directing in electrophilic substitution?
31 votes

how is anilinium ion meta directing for electrophiles? Actually, anilinium is not meta directing (I know it is often taught that way), but rather it inductively deactivates the entire aromatic ring. ...

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Can an atom bond with more than 8 other atoms?
31 votes

14 coordination is claimed in $\ce{U(BH4)4}$ (ref_1, p. 268). The molecule exists as a polymer in the solid state. Six hydrogens from two of the $\ce{BH4}$ groups bond between the boron and uranium (...

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Which is the more stable enol form?
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29 votes

Keto-enol equilibria reflect a delicate thermodynamic balance between the two forms. The bonding differences between the keto and enol structures shown above are: keto: C=O double bond, C-C single ...

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What is a non-classical carbocation?
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29 votes

Here is a picture of a "classical" carbocation, there is an electron deficient carbon bearing a positive charge. There are many examples of "non-classical" carbocations, but the 2-norbornyl ...

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Why is 2-methylpropene less in energy than its alkene counterparts?
29 votes

There are two things we need to understand before we can answer the question. 1) More highly substituted double bonds are generally more stable than less substituted double bonds. This is because ...

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Why does diamond conduct heat better than graphite?
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29 votes

Diamond is one of the best thermal conductors known, in fact diamond is a better thermal conductor than many metals (thermal conductivity (W/m-K): aluminum=237, copper=401, diamond=895). The carbon ...

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Why do SN1 and SN2 reactions not occur at sp2 centres?
28 votes

Sometimes, especially in introductory courses the instructor will try to keep things "focused" in order to promote learning. Still, it's unfortunate that the instructor couldn't respond in a more ...

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Why are vinylic and arylic carbocations highly unstable?
28 votes

Background S-orbitals are lower in energy than p-orbitals, therefore the more s-character in an orbital, the lower its energy and the more stable any electrons occupying the orbital. In other words, ...

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Does O2 have a color in the gas phase
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28 votes

Background $\ce{O2}$ exists as a paramagnetic, triplet since the two electrons in its two (degenerate) HOMO orbitals are unpaired. There are 6 known phases of solid oxygen with color ranging from ...

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Why does cyclopropane react with bromine?
27 votes

The $\ce{H-C-H}$ angle in cyclopropane has been measured to be $114^\circ$. From this, and using Coulson's theorem $$1 + \lambda^2 \cos(114^\circ) = 0$$ where $\ce{\lambda^2}$ represents the ...

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What makes C=O more stable that C(OH)₂
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27 votes

Bond stability is the answer. The energy required to break a $\ce{C-O}$ bond is $\pu{85.5 kcal/m}$; the energy given off when a $\ce{C=O}$ bond is formed is around $\pu{178 kcal/m}$ (reference). ...

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Why does mercury have low melting and boiling points?
27 votes

Mercury is different! It is not as reactive as its neighbors in the Periodic Table, it doesn't conduct heat and electricity as well as other metals, and it is a liquid unlike other metals. The ...

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