2007-10-27 07:30:34 · 4 answers · asked by ... 2 in Science & Mathematics ➔ Chemistry
Hund's rule requires that every orbital in a sublevel should be occupied by an unpaired electron (and that all unpaired electrons should have the same spin) before any orbital receives a second electron (with the opposite spin). Hund found that in an atom, the more electrons there were that had the same spin (or the greater the multiplicity of spin), the more stable the atom is. It's commonly said that placing electrons in separate orbitals (rather than immediately packing two electrons into one orbital when other orbitals are empty) causes the electrons to be further spread out, which results in lower potential energy. While this is undoubtedly true, it isn't the real reason. Occupying every orbital before pairing up electrons decreases the amount of electron screening: in other words, it allows each electron to "feel" a greater effective nuclear charge. This will stabilize the atom a bit and lower its potential energy.
Hund's rule explains the anomolous electron configuration of atoms like chromium. Following the Aufbau principle, you would assume it to be [Ar] 4s2 3d4. Instead, you get [Ar] 4s1 3d5. You'll notice that the ACTUAL configuration of chromium's electrons allows the atom to have six half-filled orbitals (rather than 4), giving it greater stability in accordance with Hund's rule.
2007-10-27 07:48:25 · answer #1 · answered by Lucas C 7 · 0⤊ 0⤋
Hunds Rules
2016-11-08 05:36:38 · answer #2 · answered by ? 4 · 0⤊ 0⤋
What you are showing is Hund's rule. Electrons do not like to share orbitals in the p, d, or f sublevels unless they have to since they have the same charge. To share an orbital they have to have opposite spins, so they prefer being alone in an orbital. Hund said you fill a sublevel with 1 electron per orbital before you start putting two electrons together in an orbital. So you would put one in each of the 2px 2py and 2pz orbitals before putting a second electron in each orbital. Pauli said that no two electrons in an atom can have the same set of 4 quantum numbers. At the least electrons have to differ in there spin quantum number
2016-03-13 11:20:40 · answer #3 · answered by Loretta 4 · 0⤊ 0⤋
A simplistic basis is that like-charged electrons repel one another, so they will occupy empty orbitals if available.
2007-10-27 07:37:55 · answer #4 · answered by steve_geo1 7 · 1⤊ 0⤋