Across a row in the periodic table, the ionization energy ________
A)increases because the n quantum number changes.
B)increases because the quantum number changes.
C)decreases because the effective nuclear charge decreases.
D)increases because the effective nuclear charge increases.
E)changes little because the outer electrons are all in the same shell.

Question

Across a row in the periodic table, the ionization energy ________
A)increases because the n quantum number changes. 
B)increases because the quantum number changes. 
C)decreases because the effective nuclear charge decreases. 
D)increases because the effective nuclear charge increases. 
E)changes little because the outer electrons are all in the same shell.

Quizplus · Accepted Answer

Ionization energy is the energy required to remove an electron from an atom or ion. Across a row in the periodic table, the number of protons and electrons increases, which increases the effective nuclear charge. This makes it harder to remove an electron, which increases the ionization energy. Therefore, the correct choice is D: increases because the effective nuclear charge increases.

Across a Row in the Periodic Table, the Ionization Energy