Question

Account for the fact that the line that separates the metals from the nonmetals on the periodic table is diagonal downward to the right instead of horizontal or vertical.

Short answer

As you go down in the periodic table, the elements become metallic, and going right the elements become non-metallic, this is because as ionization energy increases the metallic character decreases. This trend creates a diagonal divide in the separation of the metals from the nonmetals on the periodic table.

Step-by-step solution

Defining the relationship between metallic character and ionization energy

As you go down a group the atomic radius is increasing and the electrons are going farther away from the nucleus. When we go down a group, the ionization energy falls. And ionization energy varies inversely with the metallic character of elements.

Identify the divide between the metallic and non-metallic characters in the elements of the periodic table.

We know that as ionization energy decreases the metallic character increases. So cross table, core electrons stay the same even when valence electrons are added. As effective nuclear charge increases, the valence electrons are held closer and closer to the nucleus. The ionization energy hence increases and the metallic character of elements increases.

Therefore, as you go down in the periodic table, the elements become metallic and going right the elements become non-metallic, which creates a diagonal divide.