Question

On the basis of electronegativity, which of these pairs of elements is most likely to form monatomic ions?

O and F
Cs and Rb
Ba and O
Na and K
I want to learn/understand. I will post my reasoning applying to this question once the thread becomes open.

Answer 1

From left to right across a period of elements, electronegativity increases. If the valence shell of an atom is less than half full, it requires less energy to lose an electron than to gain one. Conversely, if the valence shell is more than half full, it is easier to pull an electron into the valence shell than to donate one.

From top to bottom down a group, electronegativity decreases. This is because atomic number increases down a group, and thus there is an increased distance between the valence electrons and nucleus, or a greater atomic radius.

Alright, so this gives us a solid foundation in electronegativity trends within the periodic table. That being said we know that polyatomic ions contain more than ONE atom. From here we can apply the rules as stated in chemistry. Atoms with similar electronegativities and ionization energies tend to form polyatomic ions by sharing electrons.