43
votes
Is there radioactivity at absolute zero?
Theoretically, a radioactive material will still be radioactive at absolute zero, and its rate of decay will be $100.00\%$ of that at room temperature. Practically, at the lowest achievable ...
- 31k
40
votes
Accepted
What roles do neutrons play in an atom?
Neutrons bind with protons and one another in the nucleus through the strong force, effectively moderating the repulsive forces between the protons and stabilizing the nucleus.$^{[1]}$
$\ce{^2He}$ (2 ...
- 23.9k
27
votes
Accepted
Is it possible to speed up radioactive decay?
It is possible to modify nuclear decay rates using chemistry, though it is rare and the effect is usually very small. Here I summarize the information available in this link. You may want to see the ...
- 28.3k
22
votes
What roles do neutrons play in an atom?
In a few more words, physicists right now are confident in saying that there are four fundamental things that happen:
Protons and neutrons stick together. (The "strong nuclear interaction".)
Neutrons ...
- 321
21
votes
Accepted
Do acids really donate a proton?
Yes, according to the Arrhenius theory, acids dissociate in aqueous solution and release a proton ($\ce{H+}$). The Brønsted–Lowry defines acids ($\ce{HA}$) and bases ($\ce{B}$) in such a way that ...
- 43.8k
19
votes
Why were elements discovered "out of order" after 1950?
The synthetic trans-uranic elements (the "modern era" elements as you call them) are synthesized by bombarding a certain isotope of one element with a certain isotope of another element with a lot of ...
- 3,050
18
votes
Which atom is the smallest atom?
The volumes of the nuclei are negligible compared to the atomic radii (like a "pea in a soccer/football/cricket stadium").
The higher the nuclear charge, the closer the electrons to the ...
- 39k
17
votes
Protons and the Heisenberg principle
But in the case of protons, we are kind of certain about their
position in the atom.
Well, yeah, kind of certain. The very notion of molecular geometry arises in the Born-Oppenheimer approximation. ...
- 18.9k
16
votes
How did Mendeleev know elements from compounds or mixtures?
Please do not underestimate the scientists of 19th century. They were as creative, intelligent and perhaps more genuinely dedicated to science than the scientists of the 21st century. Spectroscopy was ...
- 38.9k
16
votes
Why do electrons jump back after absorbing energy and moving to a higher energy level?
This is a very fundamental question and for really understanding the "why" some advanced physics is involved. I will describe the process rather superficially.
As you might know, the level ...
- 2,396
15
votes
Accepted
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 ...
- 4,709
15
votes
Accepted
Why is the electron-nucleus attraction modelled with only electrostatic interactions?
If I understand the question correctly, OP is somewhat surprised that Coulomb's law is used to describe the interaction between an electron and a nucleus, although it is usually pictured that ...
- 18.9k
14
votes
Deflection of Alpha Particles in Rutherford's model of atom
See, what the Geiger-Marsden-Rutherford experiment achieved was the following: by bombarding (with alpha particles) a one-atom thick gold sheet and counting how many alpha particles passed through, ...
- 2,853
14
votes
Accepted
Why are dipoles "permanent/induced dipole permanent/induced dipole" and not just "permanent/induced dipole" once?
Because it takes two to tango.
Dipoles interact with each other. A Lone dipole has nothing to interact with (other than an electric field, but if we ignore some externally applied macro field, there ...
- 35.4k
14
votes
Accepted
Can Rydberg constant be in joules?
Authors may be sloppy about notation in this matter. I recommend considering $R_\ce{H} \approx \pu{10973 cm-1}$ and $Ry \approx \pu{2.18e-18 J}$, noting $Ry = hc \cdot R_\ce{H}$. Units of wavenumbers $...
- 2,194
14
votes
Accepted
Why does the same electron transition release photons of different frequencies for some elements?
I am glad that you updated the question because it highlights a very common misconception. First of all the JavaLab Flame Test is completely wrong for both copper, calcium and many more salts ...
- 38.9k
13
votes
Why do atoms need 8 electrons to stabilize?
The valence orbitals of atoms are composed of suborbitals (s and p) there is 1 s suborbital which is spherical and can hold 2 electrons (one with up spin and one with down spin). There are 3 p ...
- 12.4k
13
votes
Accepted
NMR chemical shift range of different elements
The are a number of important factors that contribute to the shielding of a nucleus. Chemical shifts arise due to differences in the local magnetic field in the different environments within a ...
- 11.9k
13
votes
Accepted
Carbon tetraradical
In its ground state, naked carbon is triplet $^3P$, with two metastable singlet states $^1D$ and $^1S$ ($^1D$ being the one that participates in most reactions) while the tetraradical is the least ...
- 14.2k
13
votes
Accepted
Why is the $\mathrm d_{z^2}$ orbital so different from the rest?
The Wikipedia is helpful in explaining why radial variations should arise in the density of non-s orbitals:
The non radial-symmetry properties of non-s orbitals are necessary to localize a particle ...
- 20.8k
11
votes
Accepted
Why do electrons need to be paired?
Wouldn’t it better to just fill them up with single electrons, as per
Hund’s rule, and then leave them like that? Would that not be more
energetically favorable?
You have to consider two ...
- 18.9k
11
votes
Accepted
Can we recycle garbage with the principles of mass spectrometry?
Yes it is possible, but is very expensive and would be orders of magnitude more costly than what people are willing to pay for recycled materials. Let me give two data points to explain why it is ...
- 21.8k
11
votes
Accepted
Schrödinger's equation and spin quantum number
Good question.
This was one indication that there had to be something more than just the Schrodinger equation. Another problem which was perceived quite quickly is that the Schrodinger equation ...
- 12.9k
10
votes
NMR chemical shift range of different elements
I only want to add some data and quotes to supplement long's answer. I am also indebted to long since the reference he provided was what helped me to find these pieces of information.
As already ...
- 71.1k
10
votes
Why can a sigma bond rotate?
Sigma bonds are defined as having their electron density along the bond axis, while pi bonds have their electron density above and below the bond axis. What this mean is that pi ...
- 171
10
votes
Accepted
Democritus vs John Dalton atomic theory
Demokrit was a philosopher, while Dalton was arguing on the basis of (somewhat limited, but still) solid, quantitative evidence. I'm not knocking Demokrit (!), but his was not a scientific statement, ...
- 12k
10
votes
Accepted
Why were elements discovered "out of order" after 1950?
The major reason is arguably nothing to do with chemistry (unless you count nuclear physics as nuclear chemistry).
The big issue is that nuclear stability isn't linear with atomic number. Some ...
- 35.4k
10
votes
What is the difference between ''1 C atom and 1 mole of C atoms?''
What is the difference between one egg and one dozen eggs? A dozen is simply a certain count, in this case 12, that is rendered as one unit for our convenience. Avogadro's number s just the same ...
- 53.1k
Only top scored, non community-wiki answers of a minimum length are eligible