Each of the following questions consists of two statements, I in the left-hand column and II in the right-hand column. For each question, determine whether statement I is true or false and whether statement II is true or false. Select the appropriate answer combination from the choices below. Choices with a filled CE oval denote that statement II is a correct explanation of the true statement I.
| Potassium has a lower first ionization energy than lithium has |
|
potassium has more protons in its nucleus than lithium has. |
Select an Answer
View Correct Answer
Ionization energy depends on effective nuclear charge and the distance of the electron from the nucleus. Outer electrons are partially shielded from the nucleus by inner electrons, so the effective nuclear charge is about the same for atoms of elements in the same group of the periodic table. Potassium 
and lithium 
are in the same group of the periodic table, but the lithium atom has fewer occupied shells and a smaller atomic radius. The outermost electron in 
is in a shell that is close to the nucleus, and the outermost electron in 
is in a shell that is relatively far from the nucleus. Therefore, there is less attraction between the outermost electron in a atom and its nucleus than between the outermost electron in a 
atom and its nucleus, and it is easier to remove an electron from a 
atom, resulting in a lower first ionization energy for 
than for 
. It is true that 
(atomic
number 
) has more protons in its nucleus than does 
(atomic number 
), but this is not the reason for the relative ionization energies. (Note, for example, that 
has more protons in its nucleus than does , but has a higher first ionization energy than does 
.) The correct answer is true, true, not a correct explanation.