what is the chemistry definition of orbital and orbit?

Question

i would realyy apreciate it, if you help me, thanks

Answer 1

The old notion (Rutherford planetary) model of the atom treated the electron as if it were a planet orbiting the sun. This implies a very specific location that can be measured and observed.

The modern theory is that electron is somewhere within a specific region around the nucleus. We cannot know exactly where at any given moment (uncertainty principle). So we use the name orbital instead of an orbit.

Answer 2

Orbital: The region of space around the nucleus of an atom where an electron is likely to be found
Orbit: The path through space of one celestial body or spacecraft about another.

Answer 3

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Thank you very much for this opportunity :-) == Edit: If you are interested just in the position uncertainty problem and not in thermodynamics, please scroll to the end of my contribution. == I should point out in the first place that quantum mechanics offers us one more level of uncertainty besides the one hidden in wave functions: in some cases, we don't either know which wave function to use! You would have to keep a list of possible wavefunctions (but only if there are just finitely many of them!) along with a list of their respective probabilities, which would be long and complicated. For such cases, a more general approach is designed: mixed states [1]. Thermal equilibrium states are a great example of this "chaos". The probability of each energy (Hamiltonian) eigenstate is proportional to exp(-E/kT), much like in Maxwell distribution [2]. Note this is probability in a classical sense, it is not a square of some probability amplitude. T is the temperature of the surroundings our system is in thermal equilibrium with. You can either define entropy of a mixed quantum state following the classical definition -k*sum(p_i ln p_i), where you plug the probabilities of the individual wavefunctions. In density matrix approach, this formula becomes -k*Tr(rho ln rho) [4], where the logarithm of a Hermitian matrix is defined as power series and converges due to the properties of rho, or can be computed using diagonalisation. As the temperature goes down, the probability concentrates on the lower energy states and the entropy decreases. In a hypothetical zero temperature state, the mixed state would become a pure state (just one wave function), the eigenstate of Hamiltonian corresponding to the lowest energy possible. For simplicity, I will assume there is just one such state, that the lowest energy state is not degenerate. So if we are talking about cooling down one atom (which is by the way nonsense in classical physics, because you need a rather big ensemble of particles to define thermodynamics), giving it zero temperature is equivalent to setting it in lowest energy state. (Note that an atom can perfectly be in such state without thermal equilibrium!) For a hydrogenium atom, this is a state 1s of the electron. Again for simplicity, I will skip a discussion about spin. Notice I didn't need to talk about any motion which would be stopped! The eigenstate of energy is quite close to this approach: it is a stationary state by definition, it does not change over time [3]. As you very probably know, this is a state where the electron is NOT localised, its probability is concentrated near a spherical shell around the nucleus of some radius. So this is your answer. Heisenberg uncertainty principle is universal. It holds in any situation. In one formulation, it tells you how "well" are you able to stop a particle's motion. But again, cooling something does not mean stopping it (in quantum world). So that Heisenberg relation holds in our case just like it holds in any case, but it is not a reason. Hope this helps! Have a nice day. Edit: obviously the original asker used the term "to freeze" in a different way. Most probably by stopping the time evolution. To have a perfectly localized particle, its wavefunction would need to be hypothetically proportional to Dirac's delta (generalized) function [5]. So the question that naturally arises is whether we can get such a wavefunction during a time evolution from some "normal" initial state. The answer is NO for several reasons (for example, looking at what the initial state should be, it can't be any normalized wavefunction). Most (or maybe any) generally considered state spaces do not contain generalized functions at all. I think the answer is the electron(s) in atom is not orbiting anything. For example, any energy eigenstate (which is exactly what one calls "orbitals" [6]) is, as mentioned above, a stationary state. It does not change over time, the electron is "anywhere" but "stays there". So stopping time would change nothing. Again as in the example of 1s state, the electrons are not localised in any moment in such scenarios. Hope this helps!

Answer 4

First of it really not realyy.. second if you don't know this answer maybe you shouldn't be on here but at school or a college. Just saying :P

Answer 5

RE:
what is the chemistry definition of orbital and orbit?
i would realyy apreciate it, if you help me, thanks