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16
votes
2answers
9k views

Electronegativity Considerations in Assigning Oxidation States

I have never seen anything other than a set of rules like these when textbooks present how to assign oxidation numbers. Such as these: However, if we keep in mind that oxidation numbers are simply ...
11
votes
2answers
3k views

Quick and simple explanation of molar mass, molecular mass and atomic mass

As a physics student, I hardly deal with such quantities and when I do, I blunder through. I think it’s a good time to be given a good explanation for these since I’m in a class of Nuclear physics. I ...
45
votes
1answer
28k views

Mechanism of arene side chain oxidation by permanganate

When treated with hot, concentrated acidic $\ce{KMnO4}$, arenes are oxidised to the corresponding carboxylic acids. For example, toluene is oxidised to benzoic acid. I've tried to examine how this ...
21
votes
3answers
7k views

Why is the inversion barrier larger in PH3 than it is in NH3?

The inversion barrier in $\ce{NH3}$ is approximately $5~\mathrm{kcal~mol^{-1}}$ and that of $\ce{PH3}$ is $35~\mathrm{kcal~mol^{-1}}$. This has well-known stereochemical consequences in that amines ...
16
votes
5answers
25k views

Metal Compounds that bond covalently [closed]

I would like to ask if anyone has a list or knows which covalent compounds have metals in them. For example, beryllium and aluminium are both metals but they bond covalently with chlorine to form ...
11
votes
2answers
2k views

How do you name an alkene using IUPAC rules if the longest carbon chain in this alkene does not include the double bond?

For example, which is the right way to name this compound: Is it 2-bromo-4-methylenehexane or 4-bromo-2-ethylpent-1-ene? Does the larger number of carbon in a chain take priority, as in the former, ...
10
votes
2answers
29k views

Hybridization of sulfur in sulfur dioxide

One of the canonical structures for sulfur dioxide - $\ce{SO2}$ - has sulfur (with a lone electron pair) double bonded to each oxygen atom to form a total of 4 bonds for sulfur - which can be achieved ...
8
votes
5answers
7k views

Is Bond Formation “Strictly” Exothermic?

Is bond formation "strictly" exothermic? The IUPAC definition of exothermic doesn't make any reference to bond formation. However, I have seen the aforementioned statement before - that bond formation ...
12
votes
2answers
26k views

Do coefficients matter in rate law?

For reaction $\ce{2A→B}$ (elementary step), according to the rate law, rate $= k [A]^2$. In some calculations, we use $k[A]^2$ as the production rate of B. Why isn't it ${1 \over 2} k[A]^2$? In this ...
16
votes
3answers
8k views

Which one is the best notation for sodium acetate

I have seen two different notations for sodium acetate. The first one is: $$\text{NaCH}_3\text{COO}$$ The second one is: $$\text{CH}_3\text{COONa}$$ Now I'm confused, which one is the best to use?
8
votes
3answers
10k views

π Bonding in Carbon Dioxide

I am fairly sure the first diagram I drew for carbon dioxide is wrong in terms of showing π bonding. This is because we use a π orbital twice, which isn't possible. The second diagram corrects this by ...
8
votes
1answer
1k views

Units of mass on the atomic scale

what are the systems of recording atomic masses and their units? I know that the nucleon number is the number of protons and neutrons I also know that the mass number on the periodic table is the ...
41
votes
4answers
47k views

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

Most books refer to a steep rise in pH when a titration reaches the equivalence point. However, I do not understand why … I mean I am adding the same drops of acid to the alkali but just as I near the ...
113
votes
7answers
67k views

Is a negative pH level physically possible?

A friend of mine was looking over the definition of pH, and wondering if it is possible to have a negative pH level. From the equation below, it certainly seems possible—just have a $1.1$ (or ...
47
votes
5answers
8k views

How can antibonding orbitals be more antibonding than bonding orbitals are bonding?

In molecular orbital theory, the fact that a bonding and antibonding molecular orbital pair have different energies is accompanied by the fact that the energy by which the bonding is lowered is less ...
24
votes
1answer
17k views

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

Other isomers include 1-butene, cis 2-butene, and trans 2-butene. Why would 2-methylpropene be less in energy if there is more steric hindrance?
28
votes
2answers
17k views

Which carbocation is more stable, the ethyl- or 1-propyl-carbocation?

$\ce{C2H5+ vs \ C3H7+}$ There are two conflicting trends here. Inductive effect of ethyl will be higher than that of methyl so carbocation attached to ethyl (3 carbons in total) should be more stable....
31
votes
3answers
34k views

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

In my textbook it is written that the order of basic strength of pnictogen hydrides is $$\ce{NH3 > PH3 > AsH3 > SbH3 > BiH3}$$ I tried but could not find any explanation as to why this ...
16
votes
1answer
16k views

Relative acidities of alkanes, alkenes, and alkynes

How does one explain the trend in bond lengths and acidity of the following hydrocarbons? $$\begin{array}{ccc} \hline \text{Species} & \ce{C-H}\text{ bond length / Å} & \mathrm{p}K_\mathrm{a} ...
22
votes
1answer
25k views

Why does mercury have low melting and boiling points?

Many metals have relatively high melting and boiling points, but mercury has relatively low melting and boiling points. What are the possible reasons for this?
17
votes
2answers
10k views

How should the hydrated proton be represented in chemical equations?

I learned the equation $$\ce{H2O + H+ -> H3O+}$$ And I know $\ce{H+}$ and $\ce{H3O+}$ really mean the same thing. But I am confused as to when I should use $\ce{H+}$ and when I should use $\ce{...
15
votes
3answers
16k views

Why is electron gain generally exothermic?

I understand that we need to supply energy to counter the nuclear attraction when we remove electrons, and that is the reason why ionization energy is endothermic. However, why does an atom release ...
12
votes
1answer
50k views

What is the major product on chlorination of 2-methylbutane?

I came across a question asking for the major product on chlorination of 2-methylbutane. The answer in the back of the book says it will be 2-chloro-3-methylbutane. However, I thought the major ...
9
votes
2answers
2k views

Le Châtelier's Principle and heat

Consider the following reaction at equilibrium. $$\ce{A->B}, \Delta H < 0 $$ Suppose I increase the temperature. Now, quite a few people would invoke Le Châtelier's Principle and say that since ...
62
votes
4answers
52k views

How can one explain niobium’s weird electronic configuration?

As cited in an answer to this question, the ground state electronic configuration of niobium is: $\ce{Nb: [Kr] 5s^1 4d^4}$ Why is that so? What factors stabilize this configuration, compared to ...
23
votes
4answers
29k views

Why does the energy gap for π - π* transitions shrink with the size of the pi-conjugated system?

Quoting from this site: As conjugated pi systems become larger, the energy gap for a π - π* transition becomes increasingly narrow, and the wavelength of light absorbed correspondingly becomes ...
16
votes
3answers
62k views

Which is the more stable enol form?

If I understand correctly, when we go from a keto to an enol form, we simply abstract an alpha proton and thereby create a double bond to a carbon-bearing the hydroxyl functional group. When ...
39
votes
3answers
108k views

What is the inert pair effect?

I was reading about the p-block elements and found that the inert pair effect is mentioned everywhere in this topic. However, the book does not explain it very well. So, what is the inert pair effect? ...
27
votes
3answers
27k views

Why do salts such as NaCl dissolve?

If we look at solubility of salts in water, we are told that they disassociate, because the positive $\ce{Na}$ ion is attracted to the partially negative oxygen in water and the negative $\ce{Cl}$ is ...
21
votes
5answers
272k views

How to determine number of structural isomers?

I have come across many questions where I'm asked to give the number of possible structural isomers. For example number, structural isomers of hexane is 5, while the number structural isomers of ...
28
votes
2answers
97k views

How do non-polar substances dissolve in non-polar solvents?

The case of polar solvents is clear to me - we get an attraction between opposite charges. However, how do non-polar substances dissolve in non-polar solvents? How could it be explained on a molecular ...
23
votes
1answer
19k views

Is cyclobutadiene antiaromatic?

Cyclobutadiene is very unstable. But, some sources claim that this instability can be attributed to other factors such as ring and angle strain rather than antiaromaticity. According to some, ...
39
votes
1answer
11k views

Can 100% covalent bonds exist?

Every covalent bond has some ionic character and every ionic bond some covalent character. I can understand why a completely ionic bond is an ideal situation. But completely covalent bonds can exist(?)...
25
votes
3answers
177k views

How does one tell if a specific molecule is acidic or basic?

Let's take the $\ce{KOH}$ molecule into account. I know it is a base from literature, but how would one go about determining if a molecule is acidic or basic simply based on the structure of the ...
14
votes
1answer
9k views

What is Sodium Chloride like in gas state?

Since sodium chloride is sodium and chlorine atoms bonded as a lattice and there are no discrete molecules, doesn't that mean in gas state, sodium chloride is simply sodium and chlorine atoms separate ...
56
votes
8answers
69k views

Is iron in the brown ring compound in a +1 oxidation state?

In the standard brown ring test for the nitrate ion, the brown ring complex is: $$\ce{[Fe(H2O)5(NO)]^{2+}}$$ In this compound, the nitrosyl ligand is positively charged, and iron is in a $+1$ ...
31
votes
1answer
30k views

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

If we make a resonance structure for the anilinium ion, with positive charge at either the ortho or the para position, we get a pentavalent nitrogen, which is not possible. So, how is the $\ce{-NH3+}$ ...
34
votes
5answers
16k views

Is pyrene aromatic despite failing Hückel's rule?

Pyrene doesn't seem to be aromatic. However, sources claim that it is aromatic. Considerations: Pyrene is cyclic. ✓ Pyrene is flat (planar). ✓ Pyrene has 16 π electrons. Every atom in the ring ...
25
votes
3answers
7k views

Explanation for the trends in nucleophilicity—Orbital interactions or electrostatic attraction

The trend of halide nucleophilicity in polar protic solvents is $$\ce{I- > Br- > Cl- > F-}$$ The reasons given by Solomons and Fryhle[1], and by Wade[2] are basically as follows. Smaller ...
49
votes
3answers
4k views

What happens to a radioactive carbon dioxide molecule when its carbon-14 atom decays?

When carbon-14 decays, the decay products are nitrogen-14 and an electron (and an electron antineutrino, but that's chemically irrelevant*): $$\ce{^14_6C -> ^14_7N + e- + \overline{v_e}}$$ Let's ...
34
votes
3answers
24k views

Is methanol more acidic than water?

Methanol is slightly more acidic than water. Their $\mathrm{p}K_\mathrm{a}$ values, in water, are $15.5$ and $15.7$, respectively. All other aliphatic alcohols, however, are less acidic than water. ...
14
votes
3answers
11k views

Can the change in internal energy be nonzero if temperature is constant?

I have learnt that internal energy, $U$, is a state function and it only depends on temperature... So if $\Delta T = 0$ then $\Delta U = 0$. However when I was studying exothermic and endothermic ...
26
votes
1answer
33k views

Addition of hydrogen bromide to 1,3-butadiene: thermodynamic and kinetic control

The reaction of one equivalent of hydrogen bromide with 1,3-butadiene gives different products at under different conditions:1 The addition of hydrogen chloride also gives rise to similar products.2 ...
24
votes
4answers
4k views

Will gaseous ionic compounds be free moving ions?

I knew while learning about electrolysis that if the ionic compound is molten it becomes free moving ions. If that is the case, what will happen if I continued heating till it reaches the boiling ...
25
votes
4answers
34k views

Why is acetic acid more acidic than phenol?

Acetic acid (ethanoic acid, $\mathrm pK_\mathrm a \approx 5$) is more acidic than phenol ($\mathrm pK_\mathrm a \approx 10$), which is reflected in their reactivity with a weak base such as sodium ...
22
votes
2answers
12k views

How to rationalise the resonance structures and hybridisation of the nitrogen in a conjugated amine?

I was given the first structure, and then drew the other 5 resonance structures: First of all, are they correct? ChemBioDraw had some complaints, but as far as I can see there's the same number of ...
22
votes
2answers
6k views

What is the favoured geometry of chlorine trifluoride?

Why is the first structure on the left more stable than the second one on the right? In the first one the angle between the two pair of nonbonding electrons is about 120° which is a lot less than ...
39
votes
2answers
8k views

Why is arsenous acid denoted H3AsO3?

Inspired by this question, I'm wondering why arsenous acid is frequently denoted $\ce{H3AsO3}$, as opposed to $\ce{As(OH)3}$, which would appear to more accurately reflect its connectivity? [edit] I ...
15
votes
1answer
3k views

What are the CIP rules for cyclic substituents?

Here's what I read on Wikipedia (section "Cycles"): To handle a molecule containing one or more cycles, one must first expand it into a tree (called a hierarchical digraph by the authors) by ...
23
votes
3answers
10k views

Can heteroatoms with lone pairs be chiral centres?

If a compound has a carbon atom with four different groups covalently bonded to it, it is called asymmetric and enantiomers of the compound can exist. But imagine if one has a different central atom, ...

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