Question

How do you write the charge and full ground-state electron configuration of the monatomic ion most likely to be formed by each of the following?

(a) N
(b) Rb
(c) Br

Answer 1

Use the periodic table to find the monatomic ion most likely to be formed, then subtract or add electrons to the electron configuration of the neutral element.

Explanation:

For elements in the s- and p- blocks, there is usually only one monatomic ion that is likely to form. The charge of that ion corresponds with the column or group the element is in.
For example,
Rubidium is in group 1, so it is likely to form an ion with a 1+ charge. Nitrogen is in group 15, so it is likely to form an ion with a 3- charge. The ions likely to form will either fill or empty a main energy level.
(See full table here: http://www.sciencegeek.net/tables/PT_ions.pdf)

To write the electron configuration, you start with the normal electron configuration of the element and add or subtract the number of electrons that the charge indicates.
For example,
Rubidium will change from
`1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^1`
to
`1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6` because it loses the last electron.

Nitrogen would change from
`1s^2 2s^2 2p^3`
to
`1s^2 2s^2 2p^6` because it gains three electrons.