Question

Which of the following has highest first ionization energy? 1)Sc 2)K

Answer 1

1) `Sc`.

Explanation:

The first ionization energy refers to the energy it takes to remove one electron from an atom.

It mainly depends on the electrostatic attraction between the positive protons in the nucleus and negative electrons—if protons and electrons are more attracted to each other, then the first ionization energy would be higher, and vice versa.

Here's the periodic table, with the positions of `Sc` and `K` marked:

From this, we can see that `Sc` and `K` both have `4` energy levels.

However, there is a key difference between the two: a neutral `K` atom has `19` protons and `19` electrons, while a neutral `Sc` atom has `21` protons and `21` electrons.

So, the magnitude of attraction between the positively charged protons and negatively charged electrons is greater for `Sc` than it is for `K`. As such, it will take more energy to remove one electron—which is why it has a higher first ionization energy.

This fits with the trend of ionization energy increasing as we move right, across a period, too!