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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 ...
Ivan Neretin's user avatar
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40 votes
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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 ...
ringo's user avatar
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27 votes
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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 ...
Nicolau Saker Neto's user avatar
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 ...
CR Drost's user avatar
  • 321
21 votes
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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 ...
Klaus-Dieter Warzecha's user avatar
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 ...
levineds's user avatar
  • 3,070
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 ...
Karsten's user avatar
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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 ...
AChem's user avatar
  • 40.4k
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 ...
Paul's user avatar
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15 votes
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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 ...
Feodoran's user avatar
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15 votes
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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 ...
Wildcat's user avatar
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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, ...
schneiderfelipe's user avatar
14 votes
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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 ...
matt_black's user avatar
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14 votes
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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 ...
Buck Thorn's user avatar
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14 votes
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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 $...
electronpusher's user avatar
14 votes
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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 ...
AChem's user avatar
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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 ...
A.K.'s user avatar
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13 votes
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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 ...
long's user avatar
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13 votes
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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 ...
EJC's user avatar
  • 14.3k
11 votes
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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 ...
Curt F.'s user avatar
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11 votes
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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 ...
jheindel's user avatar
  • 13.1k
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 ...
orthocresol's user avatar
  • 71.2k
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 ...
user39636's user avatar
  • 171
10 votes
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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, ...
Karl's user avatar
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10 votes
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What is the physical state of a single atom?

This answer has been written so it hopefully can be understood by people that do not have a degree. If something is not correct, let me know, but be aware that throwing around fancy words will not ...
Raditz_35's user avatar
  • 401
10 votes
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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 ...
matt_black's user avatar
  • 36.2k
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 ...
Oscar Lanzi's user avatar
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10 votes

Can Rydberg constant be in joules?

Rydberg constant $R_∞$ is usually given in reciprocal length units historically and because it's determined from hydrogen and deuterium transition frequencies [1]. Current value (in $\pu{m-1}$) is ...
andselisk's user avatar
  • 37.7k
10 votes

How does de Broglie actually prove Bohr's postulates?

de Brogile explains why orbitals are quantised Strictly speaking de Brogile doesn't prove Bohr's postulates which are mostly wrong. But he did provide an explanation for the most important of Bohr's ...
matt_black's user avatar
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