The Stack Overflow podcast is back! Listen to an interview with our new CEO.

Hot answers tagged

13

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, ...


8

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 ...


7

Electricity is a macroscopic phenomenon. It does not depend on the notion of an electron. In 1733 Charles François de Cisternay du Fay discovered the existence of positive and negative charge. In 1800, after the invention of the voltaic pile, the first electrolysis experiments that showed the effect of electric current on water have been made. In 1833 ...


7

Yes, it will continue to be radioactive. This is because the instability of the nucleus is due to the balance of forces internal to it, not to the motion of it as a whole object. It's just like how that throwing a red ball doesn't stop it from being colored red anymore while it is in motion. Likewise, no chemical process can stabilize a radioactive nucleus ...


4

As of May 20th 2019, the Avogadro constant will be set to $6.02214076 \times 10^{23}\ \rm{mol}^{–1}$, i.e. the Avogadro constant times one mole will be an integer, but not the one the OP asked about. In preparing for the switch of definition, the BIPM looked carefully at two ways of determining the constant, and then set it to the best estimate from ...


4

Orbitals are only mathematical functions that approximate the quantum state of an electron. Not only orbitals do not visually represent atoms, but orbitals do not have physical existence, they are only mathematical objects. To really visualize atoms we have to use some topological definition of atom that uses electron density $\rho$, and then plot this ...


4

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 ...


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 ...


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 ...


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

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

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

Basically, it depends on subshell. If you google something like "subshells", you'll see that s-subshell can hold 2 electrons, p - 6, d - 10, f - 14, g - 18. It's very unlikely that you'll need subshells f and g, since you're school student. Look at this picture (about Aufbau principle). It shows you the order of orbitals. Each s orbital holds up to 2 ...


3

Another way of lookung at this problem is to identify nuclei, at least heavier ones, as having their own internal temperature. Dynamic processes take place within the nuclei, and the energy exchanged in these processes corresponds to roughly $10^{11}$ Kelvins when translated to a degree scale -- a temperature locked within the nuclei and not generally seen ...


2

I think it is a poor phrasing. The strong force is responsible for keeping quarks together inside a proton or a neutron, but also between quarks belonging to different proton/neutron (but I am not sure for proton-proton interaction because of the repulsive electromagnetic force). By contrast, the weak force is responsible for turning one type of quarks into ...


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

Unfortunately, that's not how shielding works. Shielding is the ability of electrons to shield each other from the nuclear charge. As you move right across the periodic table, the number of electrons increases but the new electrons are all in the same energy level and thus, roughly at the same distance from the nucleus. Therefore, they cannot shield each ...


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

I think your inference is correct, though the plot looks very awkward. There should be an exponential decay at large values of $r$, but in the plot the curve plunges sharply onto the $x$-axis. Also the shapes of each peak should not be so symmetric, but instead skewed towards the left.


2

In spectroscopy and related fields it is common to measure energy levels in units of reciprocal centimeters (e.g., IR and Ramon 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

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

You ask how bonding between two neutral atoms can be electrostatic. In the case of covalent and van der waals the electrostatic basis is not so obvious as it is for ionic compounds. A covalent bond forms when two neutral atoms establish a shared molecular orbital which is much larger than the separate atomic orbitals that the bonding electrons contributed by ...


1

The hydrogen atom wavefunctions can be useful for multielectron atoms as a means of looking up their size (by means of a parameterization). The hydrogen atom wavefunctions form one possible basis for the definition of effective nuclear charges, see for instance here, where Hartree–Fock orbitals are used to compute effective charges: $$ Z_{eff} = \frac{<...


Only top voted, non community-wiki answers of a minimum length are eligible