Nicolau Saker Neto
  • Member for 8 years, 9 months
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Why can we smell copper?
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196 votes

This is a nice question, as it confronts a very replicable and common experience with a well established yet seemingly contradictory fact. As you expected, the smell of metal has nothing to do with ...

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Why doesn't H₄O²⁺ exist?
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139 votes

I myself was always confused why $\ce{H3O^+}$ is so well-known and yet almost nobody talks of $\ce{H4O^2+}$. I mean, $\ce{H3O^+}$ still has a lone pair, right? Why can't another proton just latch onto ...

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Why don't everyday things burn?
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54 votes

The equilibrium constant for combustion of organic matter in air with oxygen is not small, but extremely large ($K_\mathrm{eq} \gg 1$), as is expected from a reaction that is simultaneously very ...

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The last element's atomic number
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54 votes

Nobody really knows. Using the naive Bohr model of the atom, we run into trouble around $Z=137$ as the innermost electrons would have to be moving above the speed of light. This result is because the ...

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Why do we call O2 oxygen?
51 votes

I think what you may find most helpful is to know a bit of the history of element discovery and atomic theory. The first pure substance containing only the element oxygen to be isolated was dioxygen (...

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Are there non-transparent gases?
47 votes

First, a little bit of background. Transparency is not an absolute property of a material. Every substance is opaque, so long as light has to pass through enough of it, and opacity also changes ...

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The reason behind the steep rise in pH in the acid base titration curve
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43 votes

I've decided to tackle this question in a somewhat different manner. Instead of giving the chemical intuition behind it, I wanted to check for myself if the mathematics actually work out. As far as I ...

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Why is chemistry unpredictable?
37 votes

Let me contribute two more reasons which make chemistry hard to analyse from a purely theoretical standpoint. The first one is that, viewed very abstractly, chemistry essentially relies on the study ...

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What is a word for "atom or molecule"?
34 votes

The classic catch-all term is molecular entity, often abbreviated to just entity. There's a Wikipedia page for it, which references the IUPAC Gold Book entry. Quoting from the latter: Any ...

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Do atoms form either a positive or a negative charge, but not both?
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34 votes

Actually, in theory almost all of the elements can be found with both positive and negative oxidation numbers: it's just a matter of finding a system with the proper reagents and conditions to force ...

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Why do all radioactive decay series terminate at lead?
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32 votes

There are four main decay chains for actinides and superheavy elements. This is a simple consequence of the fact that one of the main processes to increase a heavy nucleus' stability is the emission ...

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What is the strongest oxidising agent?
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31 votes

Ivan's answer is indeed thought-provoking. But let's have some fun. IUPAC defines oxidation as: The complete, net removal of one or more electrons from a molecular entity. My humble query is thus - ...

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Does IUPAC nomenclature have the ability to name all organic compounds?
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31 votes

Definitely not. You got yourself in trouble specifying all organic compounds, because there is a truly immense, mind-boggling number of possible compounds. No one even knows how to accurately ...

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How come uranium's relative atomic mass is 238.03 when it only contains isotopes with a mass number of 238 or less?
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29 votes

Approximately 99.3% of uranium on Earth is the $\mathrm{^{238}U}$ isotope, and this specific isotope has an atomic mass of $\mathrm{238.05\ u}$, where $\mathrm{u}$ is the atomic mass unit, equivalent ...

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Is it possible to melt diamonds into a liquid?
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29 votes

Liquid carbon does indeed exist, but perhaps surprisingly, relatively little is known about it. It only exists above around $4000\ \mathrm{K}$ and $100\ \mathrm{atm}$, which are not trivial conditions ...

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What are some good examples of rate equations for a math class?
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29 votes

How thoughtful of you to include chemistry in your differential equations course! We appreciate your effort, especially going the extra mile to make it realistic. I hope you've seen the rate equation ...

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Does hydrogen really have seven isotopes?
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28 votes

Yes, there are seven known isotopes of hydrogen, though only two ($\ce{^1H}$ and $\ce{^2H}$) are stable with respect to nuclear decay, and only three ($\ce{^1H}$, $\ce{^2H}$ and $\ce{^3H}$) exist/can ...

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Is it possible to speed up radioactive decay?
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25 votes

It is possible to modify nuclear decay rates using chemistry, though it is rare and the effect is usually very small. Here I summarize the information available in this link. You may want to see the ...

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What is the correct value of the Avogadro constant? And how was it derived?
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24 votes

Whenever you're looking for accurate fundamental physical constants, CODATA recommended values are the way to go. As of May 20, 2019, Avogadro's constant is now truly an exact value, with infinite ...

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Why does the 3rd electron shell start filling up with scandium?
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24 votes

The relative energies of the electronic subshells have been calculated for atoms in the vicinity of $Z=20$ (J. Chem. Educ., 1994, 71 (6), 469), and the result is surprising: Looking at this graph, by ...

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How much CO2 could you remove from the atmosphere with 2 trillion USD?
24 votes

This is very hard to answer precisely, as there are many different carbon capture strategies, and economics at the scale required is quite different from our normal understanding. However, I'd love to ...

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On heating in the Earth's atmosphere, can magnesium react with nitrogen to form magnesium nitride?
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23 votes

A large pile of grey magnesium powder, when lit in air, produces a smouldering pile which cools down to reveal a crusty white solid of magnesium oxide. However, if you break apart the mound, you can ...

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Is there a least reactive chemical species?
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23 votes

I think a good argument can be made for either helium or neon, the most noble of the noble gasses. Those are the two prototypical unreactive elements. They are the only two stable elements for which ...

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Why is the minus sign (-) not allowed in reaction equations?
23 votes

Don't get too caught up in notational rigidity. You're "allowed" to use any notation you want, if it gets you to the correct answer. If you really want, go ahead and use $\ce{Na\ - \ e^{-} -> Na+}$...

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Why does graphite have a high melting point even though its intermolecular forces are weak?
22 votes

It's not usual to consider graphite as a material composed of "molecules" in the typical sense, though it could be viewed as a kind of polymer with two-dimensional macromolecules. Regardless, it is ...

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Shape of the P1/2 Orbital
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22 votes

As orthocresol mentioned, this is all about relativity, so let's talk about it. I am hardly an expert myself, but I'll try to give an answer to the best of my limited knowledge. For an interesting and ...

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A compound that absorbs all visible light
22 votes

All metals are capable of absorbing photons of any wavelength below hard ultraviolet, as ideally there are allowed electronic transitions of arbitrarily small energy between states in the unfilled ...

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Why do cyclic hydrocarbons have higher boiling points than their acyclic isomers?
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21 votes

Your intuition is indeed correct! Several sources provide the same answer (1, 2, 3). Perhaps the simplest and most direct evidence comes from comparing the densities of the liquid unbranched alkanes ...

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Can carbon dioxide be reduced to carbon monoxide and oxygen to produce energy?
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20 votes

Unfortunately, the question as stated is thermodynamically impossible. Let's look at the proposed reaction: $$\ce{CO2(g) -> CO(g) + O(g)}$$ This reaction is simply a bond dissociation (specifically,...

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Why does radium have a higher first ionisation energy than barium?
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20 votes

I think it's also important to mention relativistic effects here. They already start becoming quite visible after $Z=70$, and $\ce{Ra}$ lies a good bit after that. In very heavy atoms, the electrons ...

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