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The answer is that when two (or more) atoms are together the whole system has changed and $n$ cannot be used in the same way as for a single atom. I find a helpful way of thinking about this is interms of molecular orbitals. Two atomic orbitals can be combined to form two molecular orbitals - one bonding and one antibonding. This is shown below for H$_2$ ...


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Three oxygen atoms do form a molecule (look up "ozone").


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Chemical bonds occur because of the outer electron shell also known as a valence electron shell. Oxygen has six electrons and it's valence shell. An atom wants 8 electrons in its valence shell. They both decide to share two electrons. That way they both have full valence shells. NaCl works because Cl wants 1 more electron and Na wants to get 7 more. Mg needs ...


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To kick things off: you're right. Molecular vibrational excitations are exactly the same as phonon modes. We don't use that language very much because the system is too small (so we can't have things like travelling waves which have momentum, and we need to work only with stationary waves) but the analogy is indeed exact. Now, as to what exactly is ...


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In this context, vibration usually refers to the relative motion of the nuclei. In a periodic solid (crystal), vibrational modes are called phonons. We can say, for example, that a normal vibrational mode of a branch $s$ with wavevector $\mathbf{k}$ is in its $n$th excited state, or equivalently, that there are $n_{\mathbf{k}s}$ phonons of branch $s$ with ...


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Molecules aren't just sums over their constituent atoms. There's many different kinds of bonds which involve different patterns in the overlap of electron orbitals, and which affect the energy levels those electrons can occupy - I'm assuming the QP video you watched explained how "color" relates to electron energy levels. The (hydrogen-like-)atom case is ...


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The answer is that color is determined by electron transitions between different energy states. Those levels are different in molecules than they are in the component atoms where there is only a central force in atoms, whereas the multiple positive charges in molecules creates a more complex potential field for the electrons to move around within. Molecules ...


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I'll do that teacher thing and turn your question around back at you. Why isn't the spectrum of the lithium atom just the spectrum of the hydrogen atom plus the spectrum of the helium atom? And, for that matter, why is the helium spectrum not simply two copies, somehow, of the hydrogen spectrum? Why do atoms have unique spectra in the first place? The ...


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In my first year at secondary school we got to ignite hydrogen in a glass flask, then test the droplets that formed on the wall of the flask to show they were water. That was at age 11. Actually, in this day and age of safety legislation I'm not sure whether pupils are still encouraged to make explosions. Anyhow, making water from hydrogen and air is dead ...


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A very common approach for modelling the recombination dynamics in semiconductors is, $$R = An + Bnp$$ This equation assumes, Monomolecular recombination of electrons dominated over that of holes, with a rate $(s^{-1})$ given by the first term. Bimolecular recombination requires and electron and a hole. Clearly these assumptions will be material ...


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I think your assumption that orthohydrogen and parahydrogen should have different bulk magnetic properties is dubious. Magnetic behavior is strongly dominated by electronic properties, because the Bohr magneton, $$ \mu_\text{Bohr} = \frac{e\hbar}{2m_\text{electron}} $$ is larger than the nuclear magneton $$ \mu_\text{nuclear} = ...



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