How many p electrons does Se (atomic number 34) possess?
Fill up the orbitals to 34 electrons (in neutral atoms the number of electrons = number of protons = atomic number) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4 So you have 2p6 and 3p6 and 4p4 = 16 p electrons in total. If you look on the periodic table it is even simpler. S electrons fill in the first two columns of every period and p orbitals fill in the last 6 columns of every period. Se is in the third period so two full p orbitals (2 x 6 = 12 ) and Se is element 4 in the third p orbital. 12 + 4 = 16.
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