Aufbau Principle-

Aufbau principle

source : slide player.com

Aufbau (German word) means ‘building up’ according to Aufbau principle,

“The vacant sub shell having lowest energy is filled first. When this sub shell is filled  completely, then the filling of next sub-shell with higher energy starts.”

The energy level diagram is,

Order of Filling of Subshell

According to Aufbau principle energy of various sub shell  increases in the order.

1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<4f<5d<6p<7s<5f<6d<7p

1H        -1s1 2He       – 1s2 3Li        – 1s2, 2s1 4Be       -1s2, 2s2 5B        – 1s2, 2s2,2p1 6C        – 1s2,2s2,2p2 7N        – 1s2,2s2,2p3 8O        -1s2,2s2, 2p4 9F         -1s2,2s2,2p5 10Ne     -1s2, 2s2,2p6 11Na     -1s2 , 2s2, 2p6, 3s1 12Mg     -1s2, 2s2, 2p6, 3s2 13Al      -1s2 , 2s2, 2p6, 3s2, 3p1 14Si      – 1s2 ,2s2, 2p6, 3s2, 3p2 15P       – 1s2 , 2s2, 2p6, 3s2, 3p3

16S       1s2 , 2s2, 2p6, 3s2, 3p4 17Cl      1s2 , 2s2, 2p6, 3s2, 3p5 18Ar      1s2 , 2s2, 2p6, 3s2, 3p6 19K      1s2 , 2s2 , 2p6, 3s2, 3p6, 4s1 20Ca     1s2 , 2s2 , 2p6, 3s2, 3p6, 4s2 21Sc      1s2 , 2s2 , 2p6 , 3s2, 3p6, 4s2, 3d1 22Ti      1s2 , 2s2 , 2p6, 3s2, 3p6, 4s2, 3d2 23V      1s2 , 2s2 , 2p6, 3s2, 3p6, 4s2, 3d3 24Cr      1s2 , 2s2 , 2p6, 3s2, 3p6, 4s1, 3d5 25Mn     1s2 , 2s2 , 2p6, 3s2, 3p6, 4s2, 3d5 26Fe      1s2 , 2s2 , 2p6, 3s2, 3p6, 4s2, 3p6 27Co     1s2 , 2s2 , 2p6, 3s2, 3p6, 4s2, 3d7 28Ni      1s2 , 2s2 , 2p6, 3s2, 3p6, 4s2, 3d8 29Cu     1s2 , 2s2 , 2p6, 3s2, 3p6, 4s1, 3d10 30Zn     1s2 , 2s2 , 2p6, 3s2, 3p6, 4s2, 3d10

There are few  exceptions to Aufbau principle , such as

24^Cr      1s² , 2s² , 2p⁶ , 3s², 3p⁶, 4s¹, 3d⁵

29^Cu     1s² , 2s² , 2p⁶ , 3s², 3p⁶, 4s¹, 3d¹⁰

41^Nb     1s² , 2s² , 2p⁶ , 3s² , 3p⁶ , 4s² , 3d¹⁰, 4p⁶ ,  5s¹, 4d⁴

42^Mo     1s² , 2s² , 2p⁶ , 3s² , 3p⁶ , 4s² , 3d¹⁰, 4p⁶, 5s¹, 4d⁵

44^Ru     1s² , 2s² , 2p⁶ , 3s² , 3p⁶ , 4s² , 3d¹⁰, 4p⁶, 5s¹, 4d⁷

45^Rh     1s² , 2s² , 2p⁶ , 3s² , 3p⁶ , 4s², 3d¹⁰, 4p⁶, 5s¹, 4d⁸

46^Pd     1s² , 2s² , 2p⁶ , 3s² , 3p⁶ , 4s² , 3d¹⁰, 4p⁶,  5s⁰, 4d¹⁰

47^Ag     1s² , 2s² , 2p⁶ , 3s² , 3p⁶ , 4s² , 3d¹⁰, 4p⁶,  5s¹, 4d¹⁰

78^pt      1s² , 2s² , 2p⁶ , 3s² , 3p⁶ , 4s² , 3d¹⁰ , 4p⁶ , 5s² , 4d¹⁰ , 5p⁶, 6s⁰, 4f¹⁴, 5d¹⁰

79^Au     1s² , 2s² , 2p⁶ , 3s² , 3p⁶, 4s², 3d¹⁰, 4p⁶ , 5s² , 4d¹⁰ , 5p⁶, 6s¹,  4f¹⁴, 5d¹⁰

Give electronic configuration of  given ions according to Aufbau principle

₁₁Na⁺, ₁₂Mg⁺⁺, ₉F^–, ₈O^––, ₂₉Cu⁺⁺, ₂₉Cu⁺, ₂₄Cr⁺, ₂₄Cr³⁺, ₂₅Mn⁺⁺, ₂₂Ti⁺⁺, ₃₀Zn⁺⁺

No of electrons in Na⁺=11-1=10

Na⁺=1s²,2s², 2p⁶

no.of electrons in Mg⁺⁺=12-2=10

Mg⁺⁺=1s²,2s²,2p⁶

no. of electrons in F^–= 9+1=10

F^–=1s²,2s²,2p⁶

no. of electrons in O^{– –}= 8+2=10

O^{– –}=1s²,2s²,2p6

no. of electrons in Cu⁺=29-1=28

Note : When d- sub shell is present then electrons are removed from outer most shell (n), then penultimate shell (n–1)d.

Cu       1s², 2s² , 2p⁶, 3s², 3p⁶, 4s¹, 3d¹⁰

Cu⁺      1s², 2s², 2p⁶, 3s², 3p⁶, 4s⁰, 3d¹⁰

Cu⁺⁺    1s², 2s², 2p⁶, 3s², 3p⁶, 4s⁰, 3d⁹

24^Cr      1s², 2s², 2p⁶, 3s², 3p⁶, 4s¹, 3d⁵

Cr⁺       1s², 2s², 2p⁶, 3s², 3p⁶, 4s⁰, 3d⁵

Cr³⁺     1s², 2s², 2p⁶, 3s², 3p⁶, 4s⁰, 3d³

25^Mn     1s², 2s², 2p⁶, 3s²,  4s², 3d⁵

Mn⁺⁺  1s², 2s², 2p⁶, 3s², 3p⁶, 4s⁰, 3d⁵

22^Ti      1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d²

Ti⁺⁺      1s², 2s², 2p⁶ , 3s², 3p⁶, 4s⁰, 3d²

30^Zn     1s², 2s², 2p⁶, 3s², 3p⁶,  4s², 3d¹⁰

Zn⁺⁺     1s², 2s², 2p⁶, 3s², 3p⁶, 4s⁰, 3d¹⁰