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1500 questions
64
votes
4 answers
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 the obvious $\ce{5s^2 4d^3}$ (Aufbau principle), or…
F'x
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64
votes
3 answers
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, the foam dies back. Clearly there's some surfactant…
Jeremy Kemball
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63
votes
1 answer
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 this primarily have to do with a decrease in…
carb0nshel1
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63
votes
7 answers
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 flow.
However, in an electrolytic cell, the anode…
1110101001
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60
votes
4 answers
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 splashing may happen.
So, why does it get hotter…
pmod
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60
votes
2 answers
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 same electron density as the real interacting…
F'x
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60
votes
6 answers
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 oddly large proportion of software used in…
Melanie Shebel
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59
votes
4 answers
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 ten times better than the heatsink in your…
HyperLuminal
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57
votes
4 answers
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 it contains water, couldn't they've printed out…
paracetamol
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56
votes
6 answers
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.
Devgeet Patel
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56
votes
4 answers
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?
Also, will using $\ce{NaCl}$ instead of…
Peeyush Kushwaha
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56
votes
3 answers
Why do we write NH3?
We've learnt that the electropositive element is written first. Then why is ammonia written as $\ce{NH3}$ ?
Soham
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55
votes
5 answers
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 than the energy by which antibonding is raised,…
stochastic13
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55
votes
4 answers
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 the Lewis structure for all the required compounds…
Melanie Shebel
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54
votes
2 answers
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?
Ram Keswani
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