79
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Why is it wrong to use the concept of hybridization for transition metal complexes?
Tetrahedral complexes
Let's consider, for example, a tetrahedral $\ce{Ni(II)}$ complex ($\mathrm{d^8}$), like $\ce{[NiCl4]^2-}$. According to hybridisation theory, the central nickel ion has $\mathrm{...
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57
votes
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Why isn't the American nickel magnetic?
There are many types of magnetic properties, including ferromagnetism, paramagnetism, diamagnetism, antiferromagnetism, ferrimagnetism, superparamagnetism, metamagnetism, spin glasses, and ...
- 12.2k
25
votes
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What is the oxidation state of Mn in HMn(CO)5?
On negative oxidation states, in general
Although it's usually a topic that's covered relatively late in a chemistry education, negative oxidation states for transition metals[1] are actually quite ...
- 71.6k
25
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Why isn't the American nickel magnetic?
None of the US coins are magnetic (ferromagnetic), except for the 1943 Lincoln penny (Steel Cents, made in steel and zinc to save copper for ammunition during wartime), which are considered magnetic. ...
22
votes
Why isn't the orbital angular momentum also considered while calculating the magnetic moments 3d transition elements?
Simplistically speaking orbital angular momentum is present when some conditions are satisfied:
A set of orbitals are degenerate;
These orbitals can be "interconverted" by rotation about a certain ...
- 71.6k
22
votes
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Why does the Co³⁺/Co²⁺ couple have such a high reduction potential?
The electronic configuration has nothing to do with it. The reduction potentials of $\ce{Ni^3+}/\ce{Ni^2+}$, $\ce{Cu^3+}/\ce{Cu^2+}$ and $\ce{Zn^3+}/\ce{Zn^2+}$, if they have been/could be measured, ...
- 71.6k
17
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Exchange energy of d6 configuration
As @orthocresol points out, the key is that you need to compare the exchange energy before vs after the ionization process. Anything that is unchanged by ionization cannot affect ionization energy. ...
- 837
16
votes
Why is anhydrous copper(II) sulfate white while the pentahydrate is blue, even though both have one unpaired electron?
Let's compare the two compounds, here I plotted the $\ce{Cu(II)}$ centers of $\ce{CuSO4.5H2O}$ and $\ce{CuSO4}$ from their crystal structure data.
As you can see, it changes from a $\ce{[Cu(H2O)4[SO4]...
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16
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Why is Ni[(PPh₃)₂Cl₂] tetrahedral?
We sometimes call this type of complex 'pseudotetrahedral' since there is an isomerism from a tetrahedral to a square planar complex possible. I was unable to find the original work here but this link ...
- 4,322
15
votes
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While filling electrons, we follow Aufbau principle, but not while removing them. Why is this so?
Usually when adding electrons based on the Aufbau principle, you go from one element to the next highest one, e.g. from $\ce{Ti}: \ce{[Ar] 4s^2 3d^2}$ to $\ce{V: [Ar] 4s^2 3d^3}$. Thus you add not ...
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13
votes
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What is the most common oxidation state of gold?
It's not obvious, but common oxidation state for gold is +3. It caused by destabilization of the $5d^{10}$ orbital. Detailed explanation you can find in The Chemistry of Gold, in Chapter 1.1.3.
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13
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Why is MnO2 not a peroxide?
Peroxides contain two oxygens connected by a single bond. X-ray or neutron diffraction will show that the oxygens in $\ce{MnO2}$ are too far apart to be bonded, and therefore it is not a peroxide.
...
- 3,154
13
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Why is MnO2 not a peroxide?
The question’s logical premise is skewed. $\ce{CO2}$ is carbon(IV) oxide or carbon dioxide. But carbon(II) also exists and so does carbon(II) oxide (carbon monoxide, $\ce{CO}$). Just because there are ...
- 68.4k
13
votes
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How do I find the ground state term symbol for transition metal complexes?
To find the ground state term symbol, you should be using symmetry and group theory arguments, you shouldn't have to resort to searching Tanabe-Sugano diagrams to get the answer.
We'll start with ...
- 71.6k
13
votes
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Derivation of the Orgel diagram for octahedral d2 complexes
1. Weak-field and strong-field limits
I will adopt the description used in Figgis and Hitchman's Ligand Field Theory and Its Applications (p 5), because I cannot really phrase it better:
It is ...
- 71.6k
13
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Why is Ni[(PPh₃)₂Cl₂] tetrahedral?
Dichlorobis(triphenylphosphine)nickel(II), or $\ce{NiCl2[P(C6H5)3]2}$ in square planar form is red and diamagnetic. The blue form is paramagnetic and features tetrahedral Ni(II) centers. Both ...
- 4,384
12
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How does aqua regia dissolve gold?
The wikipedia article of aqua regia has beautifully mentioned the mechanism of gold dissolving in aqua regia:
Aqua regia dissolves gold, though neither constituent acid will do so alone, because, in ...
- 26.3k
12
votes
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If the ferric ion is more stable than the ferrous ion, then why is it readily reduced to the latter?
As already pointed out, the notion of stability needs to be defined much more accurately.
The fact that the standard reduction potential is positive has no direct bearing on the gas-phase stabilities ...
- 71.6k
12
votes
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Can aqua regia/royal water be produced with sources of chloride and nitrate other than hydrochloric acid and nitric acid?
Not even zinc would react with neutral nitrate + chloride, why should gold ?
Aqua regia must be strongly acidic for nitrates to have oxidative properties for oxidation of chlorides to chlorine and ...
- 42.7k
11
votes
Why is manganese(II) coloured although the transition should be spin-forbidden?
To continue with the answer from @orthocresol. The breaking of formally ‘ forbidden’ transitions is very common indeed, possibly the best example is in the observation of phosphorescence from almost ...
- 30.8k
11
votes
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Molecular orbital diagram of a complex including an oxido ligand
Although chemists and chemistry students alike often indiscriminatorily use the $\mathrm{t_{2g}}$ and $\mathrm{e_g}$ descriptors for the d-orbitals of a d-block metal in coordination complexes, those ...
- 68.4k
11
votes
Why is tetraamminecopper(II) a square planar and not a tetrahedral species?
The short answer is that $\ce{[Cu(NH3)4]^2+}$ does not exist; the compound you are observing is $\ce{[Cu(NH3)4(H2O)2]^2+}$. It is not square planar but a Jahn-Teller distorted octahedron. You can ...
- 68.4k
11
votes
Accepted
Is pyrite (FeS₂) an ionic or a covalent compound?
You seem to have fallen into the trap of thinking that ionic and covalent bonds are fundamentally different. They are not - they are just two ends of a spectrum, which has an arbitrary division ...
- 15.4k
11
votes
Hybridisation of Mn in potassium permanganate
I feel a bit like a broken record: Do not use hybridisation to describe coordination compounds; it is not helpful.
However, the case of permanganate stands out as something where hybridisation is ...
- 68.4k
11
votes
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Does a certain "Badecker reaction" actually exist?
The reaction in question is actually called the Boedeker reaction. How the book came from Boedeker to Badeker I do not know, but maybe there was one instance of Boedeker being written Bödeker which ...
- 68.4k
11
votes
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Are complex ions thermochromic?
Indeed, this effect is observed in certain select cases. The effect of spin-spin cross over has been mentioned in this regard. There can be some other effects at play, namely: phase transitions, ...
- 8,495
11
votes
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Why is Prussian blue ‘blue’ in colour?
Prussian blue contains both $\ce{Fe(II)}$ and $\ce{Fe(III)}$. Mixed-valence compounds, such as the one in question, absorb certain wavelengths of visible light resulting due to the phenomenon of inter ...
- 8,495
11
votes
Is scandium considered a transition metal?
It may depend on who you ask, and maybe even when you ask. The tl, dr of what is below is that we are moving towards counting scandium as a transition metal.
Wikipedia follows the IUPAC definition ...
- 60k
10
votes
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What is the nature of the Fe–O2 binding in oxymyoglobin and oxyhemoglobin?
TL;DR: It is not really "one or the other" - it is more of "somewhere in between", like a resonance hybrid. If I had to choose, I'd personally lean towards Weiss's $\ce{Fe(III)-O2-}$ model. However, ...
- 71.6k
10
votes
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Does tetraoxidovanadium (VO4+) ion exist?
Since the comment by Ivan pointing to a possible misprint got four votes and no answer yet, I'll post it as an answer. In short: this is a misprint in the book, and the book probably meant $\ce{VO2+}$...
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