Why are the trends and exceptions to the trends in ionization energy observed? check all that apply. ionization energy tends to increase down a group because the electrons get farther away from the nucleus. ionization energy tends to increase across a period because the nuclear charge increases. ionization energy tends to increase across a period because electrons are added to the same main energy level. the ionization energies of the elements in group 16 tend to be slightly smaller than the elements in group 15 because the fourth electron is added to an unfilled p orbital. the ionization energies of elements in group 13 tend to be lower than the elements in group 2 because the full s orbital shields the electron in the p orbital from the nucleus.

Ionization energy refers to the energy required to remove an electron from the atom of an element.

Ionization energy increases across the period as the size of the nuclear charge increases and attraction for the outermost electrons increases also.

Between groups 15 and 16, an electron is added to the p orbital. Recall that a half filled or completely filled orbital has unusual stability. Hence, group 15 elements are more stable since they all have half filled np orbitals. The addition of the fourth electron in group 16 elements destroys this stability hence the ionization energy of group 16 elements is less than that of group 15 elements.

The order of shielding of atomic orbitals is;  s orbitals > p orbitals> d orbitals> f orbitals. The s orbitals exhibits a strong shielding effect hence they shield the outermost np orbitals of group 13 elements from the attractive force of the nucleus. Hence, group 13 elements have a lower ionization energy than group 2 elements.

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