Question

1. choose the best answer. (see companion material, the periodical table, attached.)

which element has 2 valence electrons?
se
mt
pu
ca

Explanation:

• For Se (Selenium), it is in Group 16 of the periodic table. The general formula for the number of valence electrons for main - group elements (Groups 1 - 2 and 13 - 18) is: for Group \(n\) (\(n = 1,2,13 - 18\)), the number of valence electrons is \(n\) (for \(n=1,2\)) or \(n - 10\) (for \(n = 13 - 18\)). For Group 16 (\(n = 16\)), the number of valence electrons is \(16- 10=6\).
• For Mt (Meitnerium), it is a transition metal. Transition metals have complex electron configurations, but in general, they do not have a simple valence - electron count based on the group number in the same way as main - group elements. However, its electron configuration does not result in 2 valence electrons.
• For Pu (Plutonium), it is an actinide. Actinides have very complex electron - filling patterns due to the filling of \(5f\) orbitals, and they do not have 2 valence electrons in the simple sense of main - group valence - electron counting.
• For Ca (Calcium), it is in Group 2 of the periodic table. Using the formula for main - group elements (\(n\) represents the group number), for Group 2 (\(n = 2\)), the number of valence electrons is \(n=2\).

Answer:

Ca