Question

A space probe identifies a new element in a sample collected from an asteroid. Successive ionization energies (in attojoules per atom) for the new element are shown below. 

To what family of the periodic table does this new element probably belong?

Answer 1

The ionization energy, or ionization potential, is the energy required to remove an electron from a gaseous atom or ion altogether. The closer and more tightly bound an electron is to the nucleus, the more difficult it will be to remove, and the higher it's ionization energy will be.

Units for Ionization Energy: Ionization energy is measured in electronvolts (eV). Sometimes the molar ionization energy is expressed in J/mol.

First vs. Subsequent Ionization Energies: The first ionization energy is the energy required to remove one electron from the parent atom. The second ionization energy is the energy needed to remove a second valence electron from the univalent ion to form the divalent ion, and so on. Successive ionization energies increase. The second ionization energy is always more significant than the first ionization energy.

Ionization energies increase moving from left to right across a period (decreasing atomic radius). Ionization energy decreases moving down a group (increasing nuclear radius). Group, I elements have low ionization energies because the loss of an electron forms a stable octet. It becomes harder to remove an electron as the atomic radius decreases because the electrons are generally closer to the nucleus, which is also more positively charged.

In our present problem, If you observe the IEs sequentially, there is a large gap between the 2nd and 3rd. This suggests it is difficult to remove more than 2 two electrons. Elements that lose two electrons to become more stable are found in Group 2A (2 representing the number of electrons in the outermost valence shell).

Answer: 2 (2A)