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131

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 that? Adding to the confusion, $\ce{H4O^2+}$ is very similar to $\ce{NH4+}$, which again is extremely well-known. Even further, the methanium cation $\ce{CH5+}$...


36

When you taste salt, you're not pushing crystalline $\ce{NaCl}$ into your taste buds. It dissolves in your saliva and dissociates. When one tastes salt, the saltiness taste receptors respond specifically to the sodium cation. That type of taste receptor is a cation channel. This is why lithium and potassium cations also taste salty (though they also ...


34

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 it. If you isolate chemical species which have a very strong tendency of displaying some specific behaviour (accepting electrons, donating electrons, ...


32

Yes, cations always have a positive charge and anions always have a negative one. The difficulty is that the term cathode and anode do not always correspond to the same pole. The cathode is that pole of an electrolytic/electrochemical cell where reduction takes place (cathodic reduction) while the anode is where oxidation takes place (anodic oxidation). ...


26

First of all, let me state the obvious: Phosphorus is awesome. After we got that out of the way we can focus on why. There are many different modifications of phosphorus in nature. With increasing thermodynamic stability they are $$\ce{P_{white} -> P_{red} -> P_{violet} -> P_{black}}.$$ Apart from this there are many low molecular different ...


25

In addition to entropid's answer, let's remember why we invoke the hydronium ion $\ce{H3O+}$ in the first place. We use $\ce{H3O+}$ as a shorthand for $\ce{H+(aq)}$, which looks more like protonated water clusters of the generic formula $\ce{H+.(H2O)_{$n$}}\equiv \ce{H_{$2n+1$}O_{$n$}+}$. Almost ten years ago, a very interesting paper appeared in Science ...


23

These species usually do not exist in nature, but they can be synthesized. Silver has been reduced in liquid ammonia to give $\ce{Ag-}$. A lot of anionic metal carbonyl complexes $\ce{M(CO)_{n}^{m-}}$ have been synthesized: -1 $\ce{[V(CO)6]-}$, $\ce{[Nb(CO)6]-}$, $\ce{[Ta(CO)6]-}$, $\ce{[Mn(CO)5]-}$, $\ce{[Ir(CO)4]-}$, $\ce{[Co(CO)4]-}$, $\ce{[Rh(CO)4]-}$...


22

Usually not. Boiling point rarely exceeds 4-5 thousand kelvin. A typical ionic bound energy is about 5 eV. 1 eV is roughly 11 thousand kelvin, so ions in low-temperature vapors exist as molecules. When the temperature becomes enough to break ionic molecules, it is enough to strip one or two electrons from atoms, so high-temperature vapors will be plasma with ...


22

Actually, the initial theories before Lewis suggested that $\ce{H+}$ is the cause of acidity. However, it soon turned up that an ion as small as the nucleus of hydrogen (you may simply call it a proton) can't be created in low energy reactions due to its high polarising power. So, $\ce{H+}$ is though the cause of acidic nature in aqueous solutions, $\ce{H+}$ ...


22

Interesting question. It is much less studied and reported on than the case of non-classical carbocations, but I did find a few papers. Brown and Occolowitz (Ref.1) reported that deuterated bicyclo[3.2.1]octa-2,6-diene 1b, below, undergoes base-catalysed de-deuteration (potassium tert-butoxide in DMSO) to give 1a much faster (ca. $3 \times 10^4$) than the ...


21

There is no chemical difference, only a psychological one: how do you think about it. They are both the same thing, but many people associate $\ce{H+}$ ions with chemical reactions and protons with particle physics. A hydrogen atom has one electron and a proton, no neutron. Therefore $\ce{H+}$ is just a proton. That is why acids are sometimes referred as ...


17

The existence of $\ce{H4O^{2+}}$ has been inferred from hydrogen/deuterium isotopic exchange monitored through $\ce{^{17}O}$ NMR spectroscopy in the most extremely acidic condensed phase superacid we can make, fluoroantimonic acid ($\ce{HF:SbF5}$ or $\ce{HSbF6}$). It seems that even the slightly weaker but still very much superacidic magic acid $\ce{HSO3F:...


17

From what I was taught in Middle-school, cations are those ions that move towards the cathode, likewise anions are those ions which move towards the anode. Nope, the definitions are as follows (from the IUPAC Goldbook): cation A monoatomic or polyatomic species having one or more elementary charges of the proton. anion A monoatomic or polyatomic species ...


17

You can indeed "harden" glass by exchanging ions on the surface, but not because it turns into quartz glass. Quartz glass is mostly so robust because it has an extremely small thermal expansion coefficient, and is therefore mostly free of internal stress due to uneven cooling. Ordinary glass already gets a lot more durable when you temper it, thereby ...


16

Aromatic cations like the tropylium cation ($\ce{C7H7+}$)[1] or the cyclopropenyl cation ($\ce{C3H3+}$)[2] can coordinate to metals, creating sandwich or half-sandwich compounds. The positive charge is shared by all carbon atoms of the rings. Anderson, J. E.; Maher, E. T.; Kool, L. B. Electrochemical and spectroelectrochemical properties of the titanium ...


16

Charge separation at waterfalls with airborne ions, resulting in a potential between the base of the waterfall and the surrounding air, is a phenomenon examined by Philipp Lenard (Über die Elektrizität der Wasserfälle, Ann Phys (Leipz), 1892, 46, 584–636). The effect is real and more recent field studies, such as Characterization of ions at Alpine ...


16

Yes free $\ce{H+}$ ions, protons, really exist. Protons are constantly emanating from the sun and reaching Earth. The proton flux is continuously monitored by satellite. However, in a solution such as water, instead of bare $\ce{H+}$ ions, they are $\ce{H3O+}$ or larger ions such as $\ce{H5O2+}$ or $\ce{H9O4+}$. When $\ce{HCl}$ dissolves, the ...


15

Apart from the methods, Ringo already described, you can do a few other tests. Aluminium This is loosely translated from the German chemgapedia.de. Look at the pretty pictures. Probably the easiest test you can do is reacting it with Morin in ethanoic acidic medium. It forms a yellow-green chelate complex, which has strong fluorescence under UV light. The ...


15

Short version: We don't call bonds "physical", there are chemical bonds and other types of interactions between particles. The chemical bonds are classified this way because they make up molecules, salts, polymers and such, which are the materials chemists are interested in studying, and not particularly because of their sub-atomic/electrostatic ...


15

In addition to the species mentioned in the answer above, I found another one in Organic Chemistry by Morrison and Boyd(Seventh Edition)


15

From IUPAC Green Book [1, p. 51]: In writing the formula for a complex ion, spacing for charge number can be added (staggered arrangement), as well as parentheses: $\ce{SO4^2-}$, $\ce{(SO4)^2-}$. The staggered arrangement is now recommended. Also, as you are apparently a $\mathrm{\LaTeX}$-user, the same convention is used by default in chemformula package. ...


15

In chemistry ask "why" only after you ask "if". Given a sufficiently strong superacidic medium, $\ce{H3O^+}$ can be protonated to $\ce{H4O^{2+}}$. Evidence for this reaction, by studying isotopic exchange in a $\ce{HF + SbF5 +SO2}$ solvent, is given here. $\ce{H4O^{2+}}$ is, of course, a powerful protic acid, and it would be leveled to something weaker, ...


14

The way I understand it is (and my understanding is by no means perfect, or complete), as you pointed out correctly: a hydrogen ion is in fact a proton. The proton is a "bare charge" and as you rightly said, "tiny". a This makes it extremely reactive (in a sense), and thus in a chemical system of any sort would immediately seek out and associate with the ...


14

Of course you can take all the electrons off an atom - it is then called "fully stripped" in atomic physics. You don't need to do it to an entire mole, mind you. In accelerators one would send energetic neon ions through a background gas or a thin foil, and the interactions will result in various charge states coming out, up to and including fully stripped.


14

I can only really speak for bromine(VII). Bromine(V) is pretty common and I'm not entirely sure what's the deal with Br(I) readily disproportionating to Br(V) + Br(-1). (The tendency of Br(I) to undergo disproportionation explains why we don't see it very commonly, but why it has this tendency I'm not so sure.) This is an example of what is sometimes called ...


13

The nitroso ligand ($\ce{NO^+}$) is also one of the most commonly occurring positively charged ligands.


13

It's not as intuitive as it seems and your questions are all legitimate questions, but sometimes even good arguments can't be used as evidence in chemistry. $\ce{NaHCO3 -> Na+ + HCO3-}$, but that one doesn't involve water at all Look at this reaction: $$\ce{NaCl <=>Na+ +Cl-}$$ Even this reaction doesn't "involve" water in the schematics but is ...


13

The purpose of the salt bridge is to prevent the two half-cell solutions from mixing. It is possible to make a really bad galvanic cell by putting both half-cells in a single solution, but they rapidly self discharge as the oxidizing agent ($\ce{Cu^+}$ in your example) can diffuse through the solution and react directly with the other electrode (Zn in the ...


13

Chemistry has an organization called the International Union of Pure and Applied Chemistry (IUPAC), which sets standards for nomenclature (among other things). Chemists usually follow its recommendations. IUPAC says Ionic charge is indicated by means of a right upper index, as in $\ce{A^n+}$ or $\ce{A^n-}$ (not $\ce{A^$+n$}$ or $\ce{A^$-n$}$). and ...


13

Protons definitely participate in chemical reactions. Free protons are generally not present in liquid water because a free proton is extremely reactive, but in the upper atmosphere or in other situations where the density of matter is low there can be free protons which participate in chemical reactions. However, I completely agree with Jori that an ...


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