Video Transcript
Which of the following substances
contains both covalent and ionic bonds? (A) BaO, (B) CO2, (C) BaCO3, (D)
H2CO3, or (E) H2O.
This question is asking us about
two different types of bonds: covalent bonds and ionic bonds.
Ionic bonds often form between a
metal atom and a nonmetal atom. In an ionic bond, one or more
electrons are donated from one element on the bond to the other. NaCl, or sodium chloride, for
example, contains an ionic bond. Ionic bonds are not typically
represented visually. We assume its presence between
metal and nonmetal elements in the same structure.
A covalent bond is between a
nonmetal atom and another nonmetal atom. In a covalent bond, electrons are
shared between the atoms on either side of the bond. Covalent bonds, like the bonds
between hydrogen and oxygen in water, are typically represented as lines. In this case, we have single lines
signifying single bonds. But we could also have double or
triple lines signifying double or triple bonds.
Of the elements that appear in the
answer choices, the nonmetals are hydrogen, carbon, and oxygen. The only metal present is barium,
which can be found on the left side of the periodic table. To better understand which answer
choices contain what types of bond, let’s draw out their bonding structures.
First, three of the answer choices
— CO2, H2CO3, and H2O — contain only nonmetals. Therefore, they will contain only
covalent bonds. Since they do not contain ionic
bonds, they cannot be the correct answer to the problem. Choice (A), barium oxide, contains
a metal atom and a nonmetal atom with an ionic bond between them. However, that ionic bond is the
only bond in the structure, so choice (A) cannot be the correct answer.
Let’s take a closer look at the
remaining answer choice, barium carbonate, to confirm that it is the correct
answer. There are many ways to draw this
structure, but one common way shows the two ions, the barium ion and the carbonate
ion. The polyatomic carbonate ion is
held together by covalent bonds between its carbon atom and each of its three oxygen
atoms. When we consider what holds
together the two ions, we can infer that there is an ionic bond that connects the
barium ion to the carbonate ion, the metal cation to the polyatomic anion. Since it contains an ionic bond and
multiple covalent bonds, we can confirm that barium carbonate is the correct
answer.
So, which of the following
substances contains both covalent and ionic bonds? That’s choice (C), BaCO3.
