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Name: Pat F.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 2001 - 2002


Question:
Dear Sir: I'm teaching 8th graders that the number of electrons in energy levels is 2, 8, 8, 18, 18, 32, etc. This is the way I learned, but now my textbook says the amount of electrons in the energy levels are 2,8,18,32, etc,on these amounts I cannot teach about valance electrons or draw configurations that match the Periodic Table. Can you help?

Pat


Replies:
I may be in the minority, but I believe that we "over-teach" electron configuration(s). They work OK so long as we confine the discussion to the first two rows of the periodic table (more or less) where energy levels are widely separated, but once we get into the transition elements and begin filling 'd' orbitals, we have to start doing a shell game (pun intended).

Even in the first row, when we get to carbon, we have to invoke the sacred "electron promotion energy" and "hybridization" to "explain" the four equivalent bonds of carbon, and save our electron configuration dogma. Consider: We start off with H-like atomic orbitals and before we get to the sixth element, we already have to "make excuses"!!!

Is it any wonder that things get confusing when we get to the transition elements, when we have to say, "Oh! Yeah, the order of filling is 's', then 'p', but when from Ca, [Ar]4s2, gee whiz the d-orbitals fill before the p's and the next elements Sc, Ti,... , fill [Ar]4s2,3d1,3d2 and after we fill all the d's then we go back and fill the p's that we said filled just after the 's' orbitals.

But have no fear,students, when we go from Tc [Kr]5s2,4d5 to Ru [Kr],5s,4d7 the 'd' and 's' orbitals reverse! Sorry 'bout that.

Don't even mention what happens further down in the periodic table when the 'f' orbitals start and they fill after the 's' and before the 'd', which fill before the 'p'.

My point is that we are describing a very complicated process and try to make a simplistic picture do too much -- too much is expected from a very approximate model. We should admit up front that the model is not all that good but it provides an approximate picture so long as we do not expect too much from it.

Vince Calder


Hi, Pat !!

Do you know the sketch for fulfilling the atomic levels that follows ?
1s2
2s2  2p6
3s2  3p6  3d10
4s2  3p6  3d10  3f14
etc

The sum of electrons in each level reaches :
2
2  +  6  =  8
2  +  6  +  10  =  18
2  +  6  +  10  +  14  =  32
etc.

of course, there is a rule for the fulfillment, difficult to explain here, but easily found on text books. The noble elements follow such numbers, what corresponds to the most stable configuration.

Best regards

Alcir Grohmann


The new text book has just reorganized the electrons. The concept of valence is still possible to teach:

The first shell 1, has only two s electrons - 1s(2)

The 2nd shell 2, has two s electrons and six p electrons - 2s(2),2p(6)

So far everything is the same.

The 3rd shell 3, has two s electrons, six p electrons and ten d electrons - 3s(2),3p(6), and 3d(10).

Essentially examining each shell individually provides the concept of valence. For example, within the 3rd shell with the 18 electrons, one readily explain valence.

Unknown



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