185

Yes, this is a beautiful question. As you said, in lower rows of the periodic table, there are relativistic effects for the electrons. That is, for core electrons in gold, the electrons are traveling at a significant fraction of the speed of light (e.g., ~58% for $\ce{Au}$ $\mathrm{1s}$ electrons). This contracts the Bohr radius of the $\mathrm{1s}$ ...


130

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 aluminum, it's not relevant to this discussion; also keep in mind that where reflectance is low, absorbance is high and vice-versa). The absorption (reduced ...


68

No. There are sweet, bitter, and various other salts. (Likely, there are tasteless salts too). Pure salty taste is as far as I know exclusive for table salt, though I wouldn't bet on it. Lead and Beryllium salts are said to be sweet, though toxic. Epsom salt, $\ce{MgSO4}$, is bitter. $\ce{CuSO4}$ has an incomprehensible, persistent metallic taste. (Based on ...


61

This effect comes from the band structure of the metal, not atoms. In simplest terms (see, e.g., Ashcroft & Mermin, Solid State Physics, chapter 1) the electrons in the conduction band have a plasma frequency $\omega_{p}^{2} = 4\pi n e^{2}/m$ - this is a collective excitation of the metal. For $\ce{Cu}$ (reddish), you start exciting the plasmons around $...


60

It is entirely arbitrary whether you call it an organic compound or not, though most would not. The distinction you make that organic compounds should be found in living things is not a useful criterion. Moreover you are wrong that carbon dioxide isn't: it is both made and used by living things. Animals make it when they metabolise sugars to release energy;...


60

For the reaction, $$\ce{M -> M+ + e-}$$ the heat liberated is highest for lithium owing to its high negative $E^\circ$ value so one would think that the reaction must be most vigorous. The reason behind the more violent reactivity of potassium rather than lithium lies in kinetics and not in thermodynamics. No doubt, maximum energy is evolved with ...


51

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 ($\ce{O2}$), in 1774, though it was called "dephlogisticated air" until 1777 when Lavoisier used the term "oxygen" for the first time. This was some 30 years ...


47

I recently got a chance to attend a talk by someone who was working on developing analytical instrumentation on Mars. The interesting story is that the initial results by ion-selective electrode was that Mars soil is full of nitrates. Nobody knew on Earth that the nitrate ion selective electrode is far more responsive to perchlorate than nitrate. After ...


45

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 still accepted today.


45

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 $\...


44

TL;DR Fluorine is electronegative and can support the extra negative charge that is dispersed on the six X atoms in $\ce{SX6}$, whereas hydrogen cannot. First, let's debunk a commonly taught myth, which is that the bonding in $\ce{SF6}$ involves promotion of electrons to the 3d orbitals with a resulting $\mathrm{sp^3d^2}$ hybridisation. This is not true. ...


40

According to H.C. Urey and G. Failla, Science 15 Mar 1935, Vol. 81, Issue 2098, pp. 273, there's no difference in the taste of ordinary and heavy water.


39

Prerequisites These are the necessary prerequisites for this topic. If you're uncomfortable with any, please first head over to the corresponding links before continuing. Chemical symbols are a shorthand method of representing an element. Instead of using the full name of an element, we simply refer to it with one or two letters. $\ce{N}$ for nitrogen and $...


38

First of all, in chemistry two types of formulas exist: structural and empirical. A structural formula shows the way atoms are connected. An empirical formula only summarizes atoms and their ratios. While often an empirical formula references a molecule, there are cases when the compound in question is not molecular, or it is unknown if it is molecular. In ...


37

The geometry of the complex changes going from $\ce{[NiCl4]^2-}$ to $\ce{[PdCl4]^2-}$. Clearly this cannot be due to any change in the ligand since it is the same in both cases. It is the other factor, the metal, that leads to the difference. Consider the splitting of the $\mathrm{d}$ orbitals in a generic $\mathrm{d^8}$ complex. If it were to adopt a ...


37

TL;DR IUPAC hasn’t made up their mind, but plain old water appears to be an appropriate name. However, chemical derivatives of water may not be named using water. In Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 it is stated (P-21.1.1.2) that The common names water, ammonia, [...] are used in these recommendations but ...


37

In the original 1771 experiment, Scheele used a very simple setup consisting of a glass retort with a glass receiver (round-bottom flask). Yes, the glass was etched to some degree by the fumes, but it was not drastic enough to destroy the apparatus. From Anders Lennartson's The Chemical Works of Carl Wilhelm Scheele [1, p. 22]: 3.1 Publication 1. ...


36

The inert pair effect describes the preference of late p-block elements (elements of the 3rd to 6th main group, starting from the 4th period but getting really important for elements from the 6th period onward) to form ions whose oxidation state is 2 less than the group valency. So much for the phenomenological part. But what's the reason for this ...


36

Saltiness is perceived when alkali metal enter taste buds. From wikipedia: Saltiness is a taste produced primarily by the presence of sodium ions. Other ions of the alkali metals group also taste salty, but the further from sodium the less salty the sensation is. The size of lithium and potassium ions most closely resemble those of sodium and ...


36

Other than a nuclear reactor, the only other chance is to dump it into a volcano. Having a much higher density than magma, it will just fall through until it hits earth's mantle. Then it's really gone. OK, dissolved and diluted in the Atlantic is also quite safe. P.S. Warning: If the bullion gets stuck in the volcano, which later explodes Krakatau-style, ...


35

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 move down the column from nitrogen to bismuth, you are placing your outermost shell of electrons, including the lone pair, in a larger and more diffuse orbital (...


34

OK, first of all I want to say I really dislike the videos that this guy puts out, since he is promoting unsafe handling of chemicals. He might know what he's doing, but it's a terrible example. To the actual question: surprisingly there are nearly no sources on this. I can understand that this isn't something a lot of people would try nowadays, but I ...


34

First, why other options are not really the options: A: vinegar, being a weak acid, doesn't neutralize sulfuric acid and only dilutes it; B: solid sodium hydroxide, a strong base, does neutralize sulfuric acid, but it does so vigorously releasing substantial amount of heat per unit of time: $$\ce{2 NaOH(s) + H2SO4(aq) -> Na2SO4(aq) + 2 H2O(l)}$$ Using ...


33

Introduction The bonding situation in $\ce{(AlCl3)2}$ and $\ce{(BCl3)2}$ is nothing trivial and the reason why aluminium chloride forms dimers, while boron trichloride does not, cannot only be attributed to size. In order to understand this phenomenon we need to look at both, the monomers and the dimers, and compare them to each other. Understanding the ...


33

The grey colour is an amalgam of mercury and gold. Mercury forms amalgams with many other metals. Some are used as chemical reagents in laboratory chemistry as they have different properties than the original metals involved. Gold amalgam is much greyer than gold. Silver amalgam has been used in dentistry. Mercury has been used in the extraction of gold in ...


32

The difference between snow and ordinary ice cubes is mainly about the size of the particles. Snow is made from small, irregular crystals with many edges at a very small scale. Light is refracted or scattered by the edges (or the interface between air and the edges). Snow is white because the scattering effect of those edges dominates what happens to light ...


32

Since I will deal with all of the alkali metals in this answer, I think the question should also be broadened. There is no point in covering one single metal (sodium) without touching the others since it is the trend going down the group that we are interested in. All thermodynamic data is taken from Prof. M. Hayward's lecture notes at Oxford. So, firstly, ...


31

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 - what better way is there to remove an electron than combining it with a literal anti-electron? Yes, my friends, we shall seek to transcend the problem entirely ...


30

There is no exact definition of "organic" compound, although you can say that organic compounds must contain carbon. There is no requirement that organic compounds can be found in living things, although the name organic comes from the fact that the first compounds in this class that were discovered did come from living things. That said, $\ce{CO2}$ is in ...


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