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14

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 $(\pu{cm-1})$ and energy are often considered interchangeable in practice because they are proportional to each other by the constant value $hc$. In my notes, ...


9

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 listed at NIST [2] website (accessed 2019-06-05): $$R_∞ = \pu{10973731.568160(21) m-1}$$ Since it's an energy unit, one can convert it to SI rather trivially via ...


7

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 ideas: electron orbitals are quantised. Bohr's whole model starts with the classical idea that electrons "orbit" a nucleus. But this has several problems not ...


7

The spectral lines represent transitions between pairs of discrete energy levels in the atom; an electron is excited by absorbing the energy of a photon and a transition from one of these levels to another occurs as the photon is destroyed. Emission lines occur when the reverse process happens. If enough energy is absorbed the atom can be ionised and an ...


4

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 with angular momentum and a wave nature in an orbital where it must tend to stay away from the central attraction force, since any particle localized at the ...


4

The dilithium dimer exists- but it isn’t particularly common, and we usually only see it in the gas phase. Essentially, the 2s electrons interact and form a bonding orbital. (s-p mixing is particularly pronounced here, but I presume you don’t know MO Theory.) Due to the diffuse nature of lithium’s atomic orbitals, the bonding is pretty weak (Wikipedia ...


3

Recall that atomic number is the number of protons in the nucleus of the element. Also recall that species having the same number of protons and different number of neutrons are termed as isotopes. Isotopes are all considered the same element. $\ce{^{12}C}$ and $\ce{^{13}C}$ are both very much carbon. You may argue that its the definition that we chose that ...


3

La and Ac have $d^1$ electrons in their valence shells, rather than $f^1$ electrons. The long table you found looks like that for a several reasons. The trends going down Sc-Y-La are like those seen in groups 1 and 2. The trend going down Sc-Y-Lu is like that of groups 4 to about 10. Since lanthanide chemistry is basically that of trivalent alkali or ...


3

Natural white light had continuous spectrum, as the source - black radiator - has continuous emission in all wavelengths. Atoms emit or absorb only at the wavelengths, that are corresponding to energy differences between discreet energy levels of electrons in atoms.


3

This excerpt is from an article in J Chem Ed (J. Chem. Educ., 1961, 38 (6), p 297 DOI: 10.1021/ed038p297) describing the contents of Markovnikov's 1870 paper in Liebig’s Annalen (translated into English, I guess): So this was before the discovery of the electron, but as you can see from the diagrams, the concept of chemical structure, atoms and valence was ...


2

$\psi$ does carry a great amount of physical meaning. The annoying part is, that it doesn't represent anything directly observable. The way (non-relativistic) quantum mechanics is constructed, makes $\psi(x_i, s_i, t)$ ($x_i$ - physical coordinates of $i$-th electron, $s_i$ - spin projection on $z$ of said electron) - a direct analogue to trajectory, or, in ...


2

In theory you could go one step further, and describe things only by a Waveform a. la. quantum mechanics. If you did this, you could do away with all distinctions completely, and merely have one waveform which describes the entire system! The reasons for the different categories are practical ones. If I'm talking at what we now call the atomic level, ...


2

This is only a way of saying that the atomic number will never be a decimal number like 1.5 or 16.8 One consequence is that if you carry out an experiment which gives you a decimal number as an atomic number, then you must have a mixture or something is wrong.


2

In spectroscopy and related fields it is common to measure energy levels in units of reciprocal centimeters (e.g., IR and Raman spectroscopy). Strictly speaking, these units ($\pu{cm^{−1}}$) are not energy units, but units proportional to energies, with $hc$ being the proportionality constant (Wikipedia). In general, $hc$ can be attributed to the value $\pu{...


1

One mole of a compound does not have $\ 6.02· 10^{23}$ atoms, as you say. One mole of a compound has $\ 6.02· 10^{23}$ molecules One mole of water has $\ 6.02· 10^{23}$ molecules H2O, and $\ 3 · 6.02· 10^{23}$ atoms. One mole of H2O has $\ 6.02· 10^{23}$ atoms O, and $\ 2·6.02· 10^{23}$ atoms H.


1

Sadly nothing fancy happens that can make headlines. Atom is not a solid in a classical sense that it will break or crack if it is rapidly heated or cooled like glass. Ordinary glass will crack when liquid nitrogen is poured into it. The Sun is an example of superheated atoms or ions. Atoms start to emit light at high temperatures.


1

Gold has only one natural isotope: 197. There are artificial gold isotopes, but they do not end up in gold bars. Even if they did, their half life is measured in days so don’t expect much to remain after a year or so. The “structure” of the metal bar, or atomic arrangement, has nothing to do with its isotopic composition. Even if you were to measure ...


1

The distinctions matter because of what we can observe in nature and the lab If you want to make sense of the world around you it helps to have some coherent scheme to describe the world and classify the things in it. That scheme should map onto things we can observe. We could just describe things by their nuclear properties (the count of protons and ...


1

Here is the IUPAC definition of an element: https://doi.org/10.1351/goldbook.C01022 A species of atoms; all atoms with the same number of protons in the atomic nucleus. A pure chemical substance composed of atoms with the same number of protons in the atomic nucleus. Sometimes this concept is called the elementary substance as distinct from the ...


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