Exercises: Electron configuration

In Bohr's model, electrons followed exact orbits around the nucleus, like planets around the Sun. Today, the quantum model refers to orbitals. The figure compares the two models.

Explain in your own words what an orbital is and how it differs from an orbit in Bohr's model.

A space probe analyses the atmosphere of a planet and finds atoms whose electron configuration is $1s^2\ 2s^2\ 2p^4$.

1. a) How many electrons does each of those atoms have?
2. b) Knowing that in a neutral atom the number of electrons equals the atomic number $Z$, which element is it?

An $\text{X}^{2+}$ ion has the electron configuration $1s^2\ 2s^2\ 2p^6$.

1. a) Calculate how many electrons the ion has and deduce the atomic number of element X.
2. b) A $\text{Y}^{-}$ ion has exactly the same configuration: deduce its atomic number as well.
3. c) Using the periodic table, name elements X and Y.