Which of the four numbered elements
could react together and form a covalent compound? (A) Two and three, (B) one and two,
(C) one and three, (D) three and four, or (E) two and four.
A covalent compound contains
covalent bonds. Covalent bonds are chemical bonds
that are formed when two nonmetal atoms share one or more pairs of electrons. We need to identify which of the
four elements are nonmetals.
The highlighted region shows the
metalloids. This region also separates the
periodic table into metals and nonmetals. Elements on the right of the
staircase are nonmetals, as well as hydrogen, which is generally found on the left
side of the staircase. The other elements on the left side
of the staircase are metals. Since we know that covalent bonds
form between two nonmetals, we know that element one, a metal, cannot bond
covalently. Therefore, we can eliminate answer
choices (B) and (C), as they both contain element one.
We are left with nonmetals two,
three, and four. Element four is in group 18 of the
periodic table. Thus, it has a full outer shell of
electrons. It is known as a noble gas. As it has a full outer shell of
electrons, it is very stable and unreactive, thus will not form a covalent bond. For this reason, we can eliminate
answer choices (D) and (E), as they both contain element four.
We are left with answer choice (A),
the correct answer. Therefore, the numbered elements
that could react together and form a covalent compound are elements two and three,
or answer choice (A).