All Questions

189
votes
3answers
23k 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 ...
161
votes
8answers
126k 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 ...
158
votes
1answer
31k 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, ...
122
votes
7answers
33k 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 & oxygen put out fires instead of catalyzing them? I understand that hydrogen and water are ...
96
votes
1answer
3k 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 ...
92
votes
7answers
52k 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 ...
90
votes
8answers
19k 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 ...
87
votes
5answers
58k 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 ...
84
votes
8answers
42k 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 ...
83
votes
7answers
200k 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, ...
76
votes
5answers
77k 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 ...
75
votes
3answers
3k 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 ...
73
votes
4answers
16k 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 ...
70
votes
7answers
102k views

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 2p orbital are closer to the nucleus on average, electrons from the 2s orbital spend a very short time very close to the nucleus (...
70
votes
2answers
25k 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 ...
69
votes
6answers
17k 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 ...
68
votes
6answers
18k 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 ...
65
votes
5answers
14k 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 ...
62
votes
1answer
7k 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 ...
62
votes
1answer
3k 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 ...
61
votes
2answers
20k 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 ...
60
votes
3answers
3k 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 ...
60
votes
3answers
16k views

How does Walter White make pure crystal meth using a non-stereospecific reaction?

In the fantastic TV series Breaking Bad, Walter White, the dying chemistry teacher, takes to making crystal meth (d-methamphetamine) by several routes. Initially, he uses the common small-scale route ...
59
votes
3answers
11k 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? ...
59
votes
4answers
26k 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 ...
59
votes
3answers
4k 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, ...
53
votes
2answers
2k 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 ...
52
votes
4answers
34k 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 ...
51
votes
6answers
40k 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 ...
51
votes
3answers
9k 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 ...
50
votes
6answers
47k 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 ...
50
votes
3answers
3k 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 ...
50
votes
4answers
147k views

Why first water and 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 ...
50
votes
3answers
5k views

Why do we write NH3?

We've learnt that the electropositive element is written first. Then why is ammonia written as $\ce{NH3}$ ?
50
votes
1answer
5k 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 ...
50
votes
3answers
11k 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 ...
50
votes
2answers
4k views

How does chloroform degrade nitrile gloves?

Many of us have experienced the failure of nitrile gloves when exposed to chloroform. What's going on at a mechanistic level when this occurs? I would guess that the chloroform dissolves some of the ...
49
votes
5answers
7k 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.
49
votes
1answer
9k views

Why does menthol (e.g. peppermint) feel cool to the tongue?

Especially when drinking water after the fact, mint can give a sharp cold sensation inside one's mouth. What process causes the sensation to occur?
48
votes
6answers
8k 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 ...
48
votes
1answer
6k views

Why doesn't frozen sugar solution taste sweet?

I'll try to make this as brief as possible: Dissolved two teaspoons of table sugar (sucrose) in about 250ml water. Sipped it, and as expected it tasted sweet. I let the rest of it sit in the freezer ...
48
votes
2answers
7k 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 ...
48
votes
2answers
13k views

Regioselectivity of acid-catalyzed ring-opening of epoxides

Not to be confused with what is the mechanism of acid-catalyzed ring opening of epoxides. What is the correct order of regioselectivity of acid-catalyzed ring-opening of epoxides: $3^\circ$ > $2^\...
48
votes
2answers
46k 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 d block. If I take for example ...
47
votes
3answers
627k 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 ...
47
votes
2answers
13k views

Why is an S-S bond stronger than an O-O bond?

I'm wondering why exactly the single bond between two sulfur atoms is stronger than that of two oxygen atoms. According to this page, an $\ce{O-O}$ bond has an enthalpy of $142~\mathrm{kJ~mol^{-1}}$, ...
44
votes
2answers
25k views

What makes banana bonds possible in diborane?

Diborane has the interesting property of having two 3-centered bonds that are each held together by only 2 electrons (see the diagram below, from Wikipedia). These are known as "banana bonds." I'm ...
43
votes
8answers
19k views

Why is the recipe of Coca Cola still a secret?

Why is the recipe for Coca-Cola still a secret? I think that given the current state of technology, it should be proficient enough to find any of the secret ingredients in Coca Cola. Any thoughts? ...
43
votes
2answers
13k 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?
43
votes
8answers
23k 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'...

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