Highest scored questions
46,142 questions
253
votes
3
answers
42k
views
Why is gold golden?
Bulk gold has a very characteristic warm yellow shine to it, whereas almost all other metals have a grey or silvery color. Where does this come from?
I have heard that this property arises from ...
- 10.9k
240
votes
1
answer
74k
views
Why can we smell copper?
If I can smell an object, it means that molecules of it are getting separated from it, so they can reach my nose. As far as I know, metals don't sublimate, especially not in room temperature. However, ...
- 2,794
183
votes
8
answers
174k
views
Can an atom have more than 8 valence electrons? If not, why is 8 the limit?
According to some chemistry textbooks, the maximum number of valence electrons for an atom is 8, but the reason for this is not explained.
So, can an atom have more than 8 valence electrons?
If ...
- 1,955
146
votes
7
answers
54k
views
Why doesn't water burn?
Hydrogen is flammable, and for any fire to burn it needs oxygen. Why does a compound made of hydrogen and oxygen put out fires instead of catalyzing them? I understand that hydrogen and water are ...
- 1,531
127
votes
7
answers
89k
views
Is a negative pH level physically possible?
A friend of mine was looking over the definition of pH and was wondering if it is possible to have a negative pH. From the equation below, it certainly seems mathematically possible—if you have a $1.1$...
- 1,389
126
votes
8
answers
32k
views
Why is absolute zero unattainable?
We were dealing with the Third Law of Thermodynamics in class, and my teacher mentioned something that we found quite fascinating:
It is physically impossible to attain a temperature of zero ...
- 18.8k
114
votes
1
answer
6k
views
Is there a general consensus on the causes of the alpha-effect?
There have been various explanations posited for the α-effect. The α-effect refers to a phenomenon wherein nucleophiles with lone pairs on atoms adjacent (i.e., in the α- position) to the atom bearing ...
- 11.9k
111
votes
5
answers
88k
views
How do you melt metals with super high melting points?
At the Renaissance fair a few years back I was watching a smith forge metal into shapes. During this time a very odd question came to me. I was wondering what the furnace was made of. My logic stated ...
- 1,233
103
votes
7
answers
338k
views
Is it actually possible to dispose of a body with hydrofluoric acid?
In the TV show "Breaking Bad", Walter White frequently gets rid of people who get in his way by submerging them in a plastic container full of hydrofluoric acid. This, at least in the TV show, ...
user1579
101
votes
7
answers
141k
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Why is the 2s orbital lower in energy than the 2p orbital when the electrons in 2s are usually farther from the nucleus?
My chemistry book explains that even though electrons in the $\mathrm{2p}$ orbital are closer to the nucleus on average, electrons from the $\mathrm{2s}$ orbital spend a very short time very close to ...
- 1,847
99
votes
2
answers
39k
views
What is Bent's rule?
I'm all bent out of shape trying to figure out what Bent's rule means. I have several formulations of it, and the most common formulation is also the hardest to understand.
Atomic s character ...
- 19.2k
97
votes
7
answers
69k
views
Is toothpaste solid or liquid?
My teacher didn't answer this properly:
Is toothpaste solid or liquid?
You can't say toothpaste is a solid because solid material have a fixed shape but toothpaste doesn't. However, you can't say ...
- 4,703
88
votes
5
answers
111k
views
Does water really 'go bad' after a couple of days?
Among my friends it is a sort of 'common wisdom' that you should throw away water after a couple of days if it was taken from the tap and stored in a bottle outside the fridge, because it has 'gone ...
- 6,750
87
votes
5
answers
20k
views
Is it true that heavy water is not blue?
I believe I saw this claim somewhere on the internet a long time ago. Specifically, it was claimed that the difference could be observed by filling one long, straight tube with light water and one ...
- 1,191
86
votes
3
answers
5k
views
If nothing sticks to Teflon, how does Teflon stick to frying pans?
The most notable characteristic of polytetrafluoroethylene (PTFE, DuPont's Teflon) is that nothing sticks to it. This complete inertness is attributed to the fluorine atoms completely shielding the ...
user95
83
votes
7
answers
27k
views
Do all salts taste salty?
Recently, I am learning the production of soluble and insoluble salts. My friend and I have done this experiment at the school lab.
We wanted to taste them to see whether they are salty are not. The ...
- 4,703
83
votes
1
answer
4k
views
What causes the old book smell?
I have a collection of old books (all 80+ years old), recently, I received a British Chemistry text from 1903 (intro page below) - this being the oldest book of my collection (112 years old at the ...
user15489
81
votes
4
answers
42k
views
Bonding in diatomic C2, a carbon-carbon quadruple bond?
Carbon is well known to form single, double, and triple $\ce{C-C}$ bonds in compounds. There is a recent report (2012) that carbon forms a quadruple bond in diatomic carbon, $\ce{C2}$. The excerpt ...
- 6,156
79
votes
7
answers
54k
views
Ortho-effect in substituted aromatic acids and bases
When comparing o,m,p-toluidine basicities, the ortho effect is believed to explain why o-toluidine is weaker. But when comparing o,m,p-toluic acid basicities, the ortho effect is stated as a reason ...
- 949
78
votes
3
answers
12k
views
Why is it wrong to use the concept of hybridization for transition metal complexes?
I have asked a lot of questions on coordination chemistry here before and I have gone through a lot others here as well. Students, including me, attempt to answer those questions using the concept of ...
- 4,197
77
votes
6
answers
26k
views
Why would breathing pure oxygen be a bad idea?
My textbook mentions that SCUBA tanks often contain a mixture of oxygen and nitrogen along with a little helium which serves as a diluent.
Now as I remember it, divers take care not to surface too ...
- 18.8k
76
votes
5
answers
23k
views
How do people know HCN smells like almonds?
I was told by my chemistry teacher that $\ce{HCN}$ smells like almonds. She then went on to tell a story about how some of her students tried to play a prank on her by pouring almond extract down the ...
- 857
75
votes
3
answers
19k
views
Could a magnet pull oxygen out of the air?
I read that the $\ce{O2}$ molecule is paramagnetic, so I'm wondering: could a strong magnet pull the $\ce{O2}$ to one part of a room – enough to cause breathing problems for the organisms in the room? ...
- 1,633
74
votes
3
answers
6k
views
How do organic chemistry mechanisms become accepted?
Now I have been learning chemistry for five years. I remember when I started organic chemistry, it was fun to draw arrows between molecules to show, as if in a mathematical demonstration, how the ...
- 4,205
72
votes
4
answers
35k
views
Why do elements in columns 6 and 11 assume 'abnormal' electron configurations?
When I look around for why copper and chromium only have one electron in their outermost s orbital and 5/10 in their outermost d orbital, I'm bombarded with the fact that they are more stable with a ...
- 1,847
70
votes
4
answers
29k
views
How does Walter White make pure crystal meth using a non-stereospecific reaction?
In the highly-rated TV series, Breaking Bad, Walter White, a high school chemistry teacher recently diagnosed with cancer, takes to making the illicit drug, crystal meth (methamphetamine), by two main ...
- 37.8k
70
votes
1
answer
12k
views
Why does F replace the axial bond in PCl5?
Why does $\ce{F}$ replace an axial bond in $\ce{PCl5}$? I realize that it would be more stable there than at equatorial bond, but what is the reason of its stability? Similarly in $\ce{AB4}$ type of ...
- 1,545
68
votes
3
answers
35k
views
Why doesn't H₄O²⁺ exist?
I know this question has been asked previously but I cannot find a satisfactory explanation as to why is it so difficult for $\ce{H4O^2+}$ to exist. There are explanations that it is so because of $+2$...
- 854
68
votes
8
answers
76k
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 $+1$ ...
- 15.3k
66
votes
9
answers
43k
views
Why do compounds like SF6 and SF4 exist but SH6 and SH4 don't?
Both $\ce{SF6}$ and $\ce{SH6}$ and $\ce{SF4}$ and $\ce{SH4}$ have the same central atom and the same hybridization, but my teacher specifically mentioned that $\ce{SH6}$ and $\ce{SH4}$ don't exist. I'...
- 769
64
votes
7
answers
601k
views
Positive or Negative Anode/Cathode in Electrolytic/Galvanic Cell
In a galvanic (voltaic) cell, the anode is considered negative and the cathode is considered positive. This seems reasonable as the anode is the source of electrons and cathode is where the electrons ...
- 3,276
64
votes
4
answers
60k
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 ...
- 23.9k
64
votes
3
answers
6k
views
Why does pasta really boil over?
I was making pasta, and I noticed the pasta boiling over. I thought about it some more, and I realized I had no idea why this was happening. When the lid is on, the foam rises. When the lid is off, ...
- 852
63
votes
1
answer
9k
views
Why does shaking a match put the fire out?
Move a match slowly and nothing happens but if you shake it violently the fire will extinguish. Oxygen makes fire grow so why does waving a flame through the oxygen rich air put the fire out? Does ...
- 739
61
votes
6
answers
13k
views
Why is FORTRAN so commonly used in computational chemistry?
I've been using Ruby to write scripts for research, but I want to get into some heavier stuff that Ruby is just too slow for. I noticed there are a few things written in C and C++, but there is an ...
- 6,802
61
votes
2
answers
4k
views
Striking examples where Kohn-Sham orbitals clearly have no physical meaning
In Density Functional Theory courses, one is often reminded that Kohn-Sham orbitals are often said to bear no any physical meaning. They only represent a noninteracting reference system which has the ...
- 23.9k
60
votes
4
answers
249k
views
Why add water first then acid?
From school, I remember a very important rule: first you need to pour the water and then the acid (when you need to mix them) not vice-versa. This is because otherwise the aсid becomes very hot and ...
- 1,053
60
votes
4
answers
18k
views
Are diamonds really forever?
Common saying. Diamond possesses:
ultra hardness, (10 on the Mohs scale; 10000 HV on Vicker's Hard Test (iron merely 30-80))
hyper thermal conductivity, ($2320~\mathrm{W\, m^{-1}\, K^{-1}}$, or over ...
- 2,257
59
votes
4
answers
29k
views
Why do shampoo ingredient labels feature the term "Aqua"?
I keep seeing the term "Aqua" in the ingredient labels on several shampoo varieties, but I really don't see why it should be there in the first place.
I mean, if the manufacturers just wanted to say ...
- 18.8k
57
votes
4
answers
386k
views
Why is it important to use a salt bridge in a voltaic cell? Can a wire be used?
I was learning about voltaic cells and came across salt bridges. If the purpose of the salt bridge is only to move electrons from an electrolyte solution to the other, then why can I not use a wire?
...
- 799
57
votes
6
answers
12k
views
The last element's atomic number
I was just thinking what can be the last atomic number that can exist within the range of permissible radioactivity limit and considering all other factors in quantum physics and chemical factors.
- 1,262
56
votes
3
answers
14k
views
Why do we write NH3?
We've learnt that the electropositive element is written first. Then why is ammonia written as $\ce{NH3}$ ?
- 1,273
56
votes
5
answers
11k
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 ...
- 6,815
55
votes
4
answers
63k
views
Is carbon dioxide organic or inorganic?
Today in chemistry class we were discussing Organic Chemistry. We discussed what organic compounds basically are and then I asked the teacher whether $\ce{CO_2}$ is organic or not. She told that it is ...
55
votes
2
answers
22k
views
Why don't we explode after drinking water?
It is known that acid should be added to water and not the opposite because it results in an exothermic reaction.
Our stomach contains HCl, so why don't we explode when we drink water?
- 747
55
votes
4
answers
799k
views
How do I figure out the hybridization of a particular atom in a molecule?
I'm learning how to apply the VSEPR theory to Lewis structures and in my homework, I'm being asked to provide the hybridization of the central atom in each Lewis structure I've drawn.
I've drawn out ...
- 6,802
55
votes
2
answers
58k
views
What makes some metals melt at higher temperature?
I'm looking at the melting temperature of metallic elements, and notice that the metals with high melting temperature are all grouped in some lower-left corner of the $\mathrm{d}$-block. If I take for ...
- 23.9k
54
votes
6
answers
89k
views
Is there any substance that's a 4-4-4 on the NFPA diamond?
A lot of the organometallics are rather... interesting compounds to work with. The most famous (among those who care, anyway) is tert-butyllithium or t-BuLi. It is the textbook example of a pyrophoric ...
- 6,734
54
votes
3
answers
27k
views
What is the reason for the exceptional stability of the cyclopropylmethyl carbocation?
Can someone explain this to me by drawing resonance structures for the cyclopropylmethyl carbocation please?
Also one more question, is the tricyclopropylmethyl carbocation more stable than tropylium ...
- 1,545
54
votes
2
answers
13k
views
What is the pH of ice?
The pH of pure liquid water depends on temperature. It is about pH = 7.0 at room temperature, pH = 6.1 at 100 °C, and pH = 7.5 at 0 °C. What happens to the pH (or to the ion product) of pure water ...
- 649