1F.5a

[Jessica Chen 2C]

Can someone explain why Na has a smaller first ionization energy than Al? Their valence electrons are both the first electrons in a subshell (3s1 vs 3p1).

[Michelle Song 1I]

Because Na also has a smaller effective nuclear charge than Al, and they have the same number of "shielding electrons".

[Jenna Ortiguerra 4G]

Typically, ionization energy increases the higher the period and as you go from left to right on the periodic table. Na is in the 3s orbital, while Al is on the 3p orbital, which is why Al has a higher ionization energy.

[Abigail Sanders 1E]

Na has a smaller first ionization energy compared to Cl as ionization energy increases across a row on the periodic table. This is because as you move across a row the numbers of protons and electrons increase making the attraction between the two greater as well. This makes it increasingly hard to remove an electron from elements like Cl.

[Natalie Nartz 4F]

The periodic trends show that ionization energy increases when moving left to right. This is because when moving left to right across a period, atomic radius decreases, so electrons are more attracted to the nucleus. With this in mind, since Na is further left, it will have a lower ionization energy than Al.