Question

What monatomic ions do barium (Z = 56) and selenium (Z = 34) form?

Short answer

$$\begin{gathered} \mathbf{a}\mathbf{.}\mathbf{}\mathbf{}{\mathbf{Ba}}^{\mathbf{+}\mathbf{2}} \\ \mathbf{b}\mathbf{.}\mathbf{}\mathbf{}{\mathbf{Se}}^{\mathbf{-}\mathbf{2}} \end{gathered}$$

Step-by-step solution

Predict the formation of anions

The elements present in group 1A, 2A, or 3A in the periodic table, lose electrons, whereas the elements present in groups 5A, 6A, or 7A in the periodic table, gains electrons to get the same number of electrons present in the nearest noble gas and form positive and negative ions respectively.

Determine the group of barium (Z = 56)

The atomic number of barium (Ba) is 56${}^{\mathbf{56}}\mathbf{Ba}$. is metal and belongs to group 2A in the periodic table.

Identify the ion barium forms

${}^{\mathbf{56}}\mathbf{Ba}$is an alkaline earth metal, so like other group 2A elements, it loses two electrons for attaining the same number of electrons present in the nearest noble gas${}^{\mathbf{56}}\mathbf{Xe}$ Hence, the monatomic ion of Ba is${\mathbf{Ba}}^{\mathbf{+}\mathbf{2}}$

Determine the group of selenium (Z = 34)

The atomic number of selenium (Se) is 34.${}^{\mathbf{34}}\mathbf{Se}$ is non-metal and belongs to group 6A in the periodic table.

 Step 5: Identify the ion selenium forms

${}^{\mathbf{34}}\mathbf{Se}$like other groups, 6A elements gain two electrons for getting the same number of electrons present in the nearest noble gas${}^{\mathbf{36}}\mathbf{Kr}$Hence, the monatomic ion of Se is${\mathbf{Se}}^{\mathbf{-}\mathbf{2}}$