1) The first ionization energies of As and Se are 947 and 941 kj/mol, respective
ID: 857121 • Letter: 1
Question
1) The first ionization energies of As and Se are 947 and 941 kj/mol, respectively.Rationalize these values in terms of electron configurations.
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2 - The successive ionization energies for an unknown element are given below.
I1 = 837 kJ/mol
I2 = 1966 kJ/mol
I3 = 16347 kJ/mol
I4 = 17948 kJ/mol
To which family in the periodic table does the unknown element most likely belong?
Explanation / Answer
1)The electron configuration of As is: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3
The electron configuration of Se is: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
Only the valence electrons matter which for As is 4p3 and for Se is 4p4. Ionization energy is the energy required to remove an electron from a gas phase atom. The first ionization energy is the energy required to remove the outermost electron from the atom. Inner electrons are closer to the nucleus which contains the positive charge in an atom, so inner electrons are held more tightly than those on the outside of the electron cloud.
As has 3 outer electrons while Se has 4 in the same orbital (the 4p orbital). Arsenic's 3 electrons are held just as tightly as 3 of the four electrons of Se, but the outermost electron of Se is held less since it is farther away from the nucleus. Therefore, the outermost 4th electron of Se is easier to remove than one of the 3 electrons that As has. So, the first ionization energy of Se is smaller than that of As since its outermost electron is easier to remove.
2)
The biggest RELATIVE jump is from 1966 to 16347 i.e. hard to lose the 3rd electron, relatively easy to lose the first two. So 2 electrons in the outer shell, hence in Group II
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