JOHN J. ALEXANDER Univwsity of Cincinnafi
Cincinnati. 45221
Using the Aufbau Principle J o h n C. Whitmer Western Washington University Bellingham, Washington 98225 General Chemistrv students should not onlv attain an understanding of the aufbau principle enablingthem to write down electron configurations. They also ought to recognize the correspondence between the quantum numbers and the structure of the oeriodic table. This auestion reauires comprehension as well as the application of knowledge to a novel situation. Other sets of rules restricting quantum numbers can he easily devised. Ouestion
T h e arrangement of elements in the periodic table can he understood in terms of the atomic orbital quantum numbers n, 1, rnr, the electron spin quantum number m, and the Pauli exclusion orinciole. Suooose .. that in a far-off ealaxv " " the rules governing these quantum numbers were slightly different. The n and 1auantum numbers are identical to ours and the Pauli exclusion principle still holds. However, m, and m, take only the following values m 1 = 0 , 1 , 2,...., 1 m, = +%,0 , -%
(a) Place the first thirty elements of this galaxy in an appropriate periodic table and explain your arrangement. (b) Which element($ of the first thirty would you expect to he most similar to element 33? Explain. Answer
(a) Since n and 1 are unchanged, the energy levels (Is, 2s, 2p, etc.) and their order of filling will remain unchanged. The restriction an mr results in ones orbital for each n, two p orbitals (mr = 0 , l )for each n > 1and threed orbitals (mr = 0 , 1 , 2 )for each n > 2. Since m, can have threevalues, the Pauli principle permits three electrons per orbital. Thus, completing rows in the periodic table will involve placing three, six and nine electrons ins, p and d orbitals, respectively. The table could be as follows
(b) Because element 33 will have the same outer electron configuration as 6and 15, it would beexpected to have similar chemical properties.
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