The maximum magnetic momentum of the ³P states is 2 and derives from the coupling of electron spin and orbital momentum in nine different combinatins (microstates) of which three have total momentum 0, three have total momentum 1 and three have total momentum 2. Most of chemistry teachers just know & teach the electronic configuration, and a SINGLE and WRONG Hund's rule, whereby a carbon atom has two paired electrons and a spin constantly equal to +½ + ½ = 1. I know this stuff is somewhat complicated, but this is a matter of facts, and you should prefer the facts to the hearsays, if you are interested to science. oxygen, #2s^2#2p^4#) the third Hund's rule applies conversely, thus the ground state will be the multiplet term with the maximum total spin. If the unfilled subshell has more than half of the maximum number of electrons (e.g. This rule says that in a multiplet if the partially filled orbitals are half-filled or less than that, (as in carbon which has two 2p electrons by a maximum occupation of six 2p electrons in the filled 2p subshell) the lowest energy state in a multiplet is the one with the minumum total spin, that is 0. There is also a third Hund's rule, that applies to carbon. But this is not the case of carbon, with only one triplet, which "wins" against the two singlets. This rule states that in these cases the ground state is the one with the highest total spin (electronic + orbital), that increases from S = 0, P =1, D=2, F = 3, G=4. The second Hund's rule applies to those states that have the same multiplicity. the one having more different values of electron spin (the superscript ³). ![]() Well, of the five states (a triple plus two singlets) ³P, ✝ and ¹S, of unionized carbon, belonging to the same electronic configuration 1s² 2s² 2p², one of the ³P states (they have very similar, but not equal energies) is the most stable (has the very lowest energy).Īmong the different states corresponding to the same most stable electronic configuration, the true ground state can be determined following the three Hund's rules.ġst Hund's rule of maximum molteplicity predicts that one of the three ³P states in the triplet should be the GROUND STATE because ³P corresponds to the state with the "highest multiplicity", i.e. One microstate corresponds to the ¹S singlet state in which the spin, the orbital and total magnetic momentum are zero. 5 microstates correspond to a so called "singlet" state ✝ in which the total electron spin is zero, whereas the total magnetic momentum is 2. We'll see that these three states in the triplet don't have exactly the same energy and only one is the * true ground state *. ![]() 9 microstates constitute the same state (and energy) called ³P, in which the total magnetic momentum can assume three different values (0, 1, 2). The two 2p electrons can be placed in 15 different combinations in the three available 2p orbitals ( #2p_x#, #2p_y#, #2p_z# corresponding to orbital magnetic momentum -1, 0, +1) and with electron spins up (↑ = +½) or down (↓ = -½). The most stable electronic configuration DOES NOT correspond to the ground state you are asking about (these are two completely different concepts), because there are usually several different states, with different energies, corresponding to the same electronic configuration, but ONLY ONE is the ground state, the one with the lowest energy.įor example, a simple six electron atom as the carbon atom has the most stable electronic configuration represented by 1s² 2s² 2p². In general, to that state correspond many different microstates having exactly the same energy, but different occupation and spin of the valence electrons in the partially filled orbitals. That value corresponds to the minimum energy that you should furnish to extract the less bounded electron from the atom, that is the first "ionization energy", and that energy is the same of the GROUND STATE. It can be experimentally recognized from the absorption spectra of the atomized element in the gas phase: there is a series of lines, in the spectrum, whose frequency reaches a maximum value. The ground state is the state that is occupied by the most part of the atoms of the same element at room temperature, because it is lower in energy.
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