A nucleus made of protons and neutrons surrounded by a cloud of electrons equal in number to the protons.

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60
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8answers
6k views

Why does space expansion not expand matter?

REFORMULATED: I have looked at the other questions (ie "why does space expansion affect matter") but can't find the answer I am looking for. My question: There is always mention of space expanding ...
55
votes
9answers
21k views

Why don't electrons crash into the nuclei they “orbit”?

I'm having trouble understanding the simple "planetary" model of the atom that I'm being taught in my basic chemistry course. In particular, I can't see how a negatively charged electron can stay ...
30
votes
4answers
3k views

What really cause light/photons to appear slower in media?

I know that if we solve the Maxwell equation, we will end up with the phase velocity of light being related to the permeability and the permittivity of the material. But this is not what I'm ...
71
votes
5answers
16k views

What does it mean for two objects to “touch”?

If you've ever been annoyingly poked by a geek, you might be familiar with the semi-nerdy obnoxious response of "I'm not actually touching you! The electrons in the atoms of my skin are just ...
18
votes
11answers
4k views

Where did Schrödinger solve the radiating problem of Bohr's model?

One of the problems with Bohr's theory to describe the hydrogen atom, was that the electron orbiting around the nucleus has an acceleration. Therefore it radiates and loses energy, until it would ...
16
votes
2answers
5k views

Dumbed-down explanation how scientists know the number of atoms in the universe?

It is often quoted that the number of atoms in the universe is 10$^{70}$ or 10$^{80}$. How do scientists determine this number? And how accurate is it (how strong is the supporting evidences for ...
8
votes
2answers
27k views

What is in the space between a nucleus of an atom and its electrons?

There is a common analogy about the structure of an atom, such as the nucleus is a fly in the centre of a sports stadium and the electrons are tiny tiny gnats circling the stadium (tip of the hat to ...
4
votes
5answers
3k views

How can the nucleus of an atom be in an excited state?

An example of the nucleus of an atom being in an excited state is the Hoyle State, which was a theory devised by the Astronomer Fred Hoyle to help describe the vast quantities of carbon-12 present in ...
18
votes
4answers
678 views

Is the electromagnetic spectrum discrete?

I'm just starting to learn physics and I have a question (that is probably stupid.) I learned that energy levels that the bound electron can have are discrete. I also learned that when an electron ...
8
votes
2answers
6k views

How does electron move around nucleus?

I need to get a nice picture about how electron moves around nucleus? I find concept of probability and orbitals quite difficult to understand?
8
votes
2answers
1k views

Do we really not know why atoms 'decide' to produce a photon?

I was watching the Cosmos documentary where Neil deGrasse Tyson explained how certain energy photons get absorbed by an atom, which causes the electrons of that atom to climb into a higher energy ...
6
votes
2answers
480 views

Why and how, in QED, can excited atoms emit photons?

The quantum mechanics of the structure of atoms as determined by the electromagnetic forces inside them correctly describes the location and coupling of the different energy levels in essentially all ...
5
votes
3answers
791 views

Why is a proton assumed to be always at the center while applying the Schrödinger equation?

Why is a proton assumed to be always at the center while applying the Schrödinger equation? Isn't it a quantum particle?
4
votes
2answers
2k views

What happens if we put together a proton and an antineutron?

A hydrogen nucleus consists of a single proton. A 2-hydrogen (deuterium) nucleus consists of a proton and a neutron. A tritium nucleus consists of a proton and two neutrons. This makes me wonder how ...
0
votes
1answer
4k views

Why isn't Hydrogen's electron pulled into the nucleus? [duplicate]

Possible Duplicate: Why do electrons occupy the space around nuclei, and not collide with them? Why don’t electrons crash into the nuclei they “orbit”? From what I learned in chemistry, ...
117
votes
3answers
11k views

How does a knife cut things at the atomic level?

As the title says. It is common sense that sharp things cut, but how do they work at the atomical level?
6
votes
2answers
1k views

The Nucleus of an Atom

We know that the protons in a nucleus are positively charged, whereas the neutrons do not possess a charge; we also know that unlike charges attract. So why does the nucleus stay intact, even though ...
5
votes
2answers
12k views

What exists in the Space between atoms

Apologies to all if this has been asked before, I searched but was unable to find one similar. This is a question that has been bugging me for a while that i haven't really been able to find a ...
4
votes
2answers
2k views

Bohr Model of the Hydrogen Atom - Energy Levels of the Hydrogen Atom

Why the allowed (stationary) orbits correspond to those for which the orbital angular momentum of the electron is an integer multiple of $\hbar=\frac {h}{2\pi}$? $$L=n\hbar$$ Bohr Quantization rule of ...
15
votes
5answers
5k views

Which experiments prove atomic theory?

Which experiments prove atomic theory? Sub-atomic theories: atoms have: nuclei; electrons; protons; and neutrons. That the number of electrons atoms have determines their relationship with other ...
9
votes
3answers
2k views

What is the quantum mechanical explanation of the octet rule?

What is the quantum mechanical explanation of the octet rule? In other words, what makes the octet rule be true from a quantum mechanical view? How we explain what makes some atoms don't follow the ...
8
votes
2answers
876 views

The distance between touching objects

What is the distance between, say, a cup of coffee and the table it rests on? What is the distance between two touching hands?
8
votes
2answers
2k views

Is the Mendeleev table explained in quantum mechanics?

Does anybody know if there exists a mathematical explanation of Mendeleev table in quantum mechanics? In some textbooks (for example in F.A.Berezin, M.A.Shubin. The Schrödinger Equation) the authors ...
1
vote
4answers
730 views

Why is the Bohr's idea of defined circular orbits overruled?

If we consider a thought experiment for determining position of an electron by using photons of light. According to principles of optics, if we use light of wavelength $\lambda$, then the position of ...
4
votes
3answers
907 views

Planetary model of atom still valid?

When I was in school, I learned (from Democritus) that an atom was similar to a solar system, with the nucleus being the sun, and the electrons being the planets. Of course, there are some ...
3
votes
0answers
107 views

What are the assumptions behind “term symbols”?

In multi-electron atoms, the electronic state of the optically active "subshell" is often expressed in "term symbols" notation. I.e. $^{2S+1}L_J$. This presumes that the system of electrons has ...
0
votes
1answer
257 views

How to determine the region that would contain a quantum particle

(a) A hydrogen atom is in its ground state. If space is divided into identical infinitesimal cubes, in which cube is the electron most likely to be found? If instead space is divided into 31 ...
29
votes
4answers
4k views

Has gravity ever been experimentally measured between two atoms?

Has there been any experiments, or are there any references, demonstrating gravity between atoms? If so, what are the key experiments/papers? Or if not, what is the smallest thing that has actually ...
15
votes
1answer
2k views

Turned to steel in the great magnetic field

This is obviously a "fun" question, but I'm sure it still has valid physics in it, so bear with me. How great of a magnetic field would you need to transmute other elements into iron/nickel, if ...
5
votes
1answer
621 views

How can we describe the electrons of multi-electron atoms (i.e. not Hydrogen) when equations/analytic solutions only exist for Hydrogen?

I've been digging into emission spectra of different elements and found that such things as the Rydberg equation, Bohr's model, and quantum mechanics can only fully describe the single electron in the ...
5
votes
3answers
373 views

Do electrons in multi-electron atoms really have definite angular momenta?

Since the mutual repulsion term between electrons orbiting the same nucleus does not commute with either electron's angular momentum operator (but only with their sum), I'd assume that the electrons ...
3
votes
2answers
325 views

Hydrogen atom: potential well and orbit radii

I happened to open up an old solid-state electronics book by Sah, and in it he says: "it is evident that the electron orbit radius is half the well radius at the energy level En" The orbit radius is ...
3
votes
1answer
579 views

Why electron clouds in atoms don't radiate? [duplicate]

I was reading that Bohr assumed electrons in orbit simply did not radiate, and my professor told me that the actual case is that electrons are clouds of probability. Even so, aren't they still moving ...
3
votes
1answer
3k views

What is heat and how does it effect an atom?

What happens in the atom when it gets heated or cooled and turns into gas, liquid or solid? I just want to know how does heat affect an atom.
3
votes
4answers
3k views

Bohr's model of an atom doesn't seem to have overcome the drawback of Rutherford's model

We, as high school students have been taught that-because Bohr's model of an atom assigns specific orbits for electrons-that it is better than Rutherford's model. But what Rutherford failed to explain ...
1
vote
1answer
110 views

How can we prove that the shape of atom is spherical? [closed]

i am looking for a derivation that can prove that the shape of an atom is spherical . I experimentally proved this statement but i need a theoretical way.
5
votes
2answers
870 views

Is it possible to recover the old Bohr-Sommerfeld model from the QM description of the atom by turning off some parameters?

Is it possible to recover the old Bohr-Sommerfeld model from the QM description of the atom by turning off some parameters? Can we use Ehrenfest's theorem (or some other scheme) to reduce the QM ...
3
votes
1answer
76 views

Why are some elemental materials grey?

How does grey occur in elemental materials such as metals? I believe that grey arises from the simultaneous reflection and absorption of all colors of the spectrum (in different atoms of course), as ...
3
votes
4answers
448 views

Is there any significance of atomic orbitals?

We have been taught that the atomic orbitals we read about are probability density region of finding electrons of particular energies which are designated by the various quantum numbers. Since, there ...
2
votes
2answers
249 views

What is Quantum jump of an electron?

Can any one define quantum jump 9 quantities jump of an electron ? I know it it is a silly question but can anyone please explain me in detail.I am a learning about the structure of atom and I want ...
2
votes
1answer
1k views

Is it that electron of an atom can be found anywhere in the space?

Simple pictures showing orbital shapes are intended to describe the angular forms of regions in space where the electrons occupying the orbital are likely to be found. The diagrams cannot, ...
1
vote
4answers
506 views

Atom Theory vs Quantum Physics

This never really occurred to me until now, so maybe it does not categorize as a really important question, but, according to Quantum Mechanics, anything that is not observed exists as a probability ...
1
vote
2answers
8k views

Comparing scales of atomic level objects to scales of everyday size objects

I am trying to come up with everyday size objects comparisions of atomic scales items, e.g. if a proton probability cloud was of size basketball how far would the next atoms to it be? reason being is ...
-1
votes
3answers
149 views

The atom, solid or liquid? [closed]

Now I know what you may be thinking, "buddy, do you realize that the quality of solid or liquid is Made by the sum total of atoms in a thing therefore an atom can't be a solid or liquid??" This, good ...
6
votes
2answers
1k views

Is Palladium an exception?

I have been taught in school that atoms cannot have more than 8 electrons in the outer shell. Palladium atom's electron configuration is 2,8,18,18. Why isn't it 2,8,18,17,1 like the case of Platinum ...
5
votes
3answers
14k views

Why is the relationship between atomic number and density not linear?

What are the factors that affect the density of an atom?
4
votes
1answer
631 views

Atoms: boson or fermion? [duplicate]

The spin of fundamental particles determines if they are bosons or fermions. The atoms also have bosonic or fermionic behavior, for example $\require{mhchem}\ce{^4He}$ has bosonic and $\ce{^3He}$ has ...
4
votes
2answers
5k views

Zero probability of finding an electron in the nucleus

One and the same electron in a p orbital and taking part in a common π (pi) bond has two lobes visualized as connecting through the nucleus. There is however zero probability of finding an electron at ...
2
votes
2answers
61 views

How do atoms in a solid “communicate” force to each other?

What is the mechanism that carries and communicates force in a solid, on the atomic level? Is there some other mechanism besides atomic deformation and proximity? That is, if I had an infinitely ...
2
votes
1answer
188 views

Question about atom subshells

So my teacher told me that EACH shell contains 5 subshells (s, p, d, f, g) but what I don't understand is this The 1st shell has only 1 subshell (and not 5 like he said) and the number of ...