Video Transcript
Which of the following options does not contain a coordinate covalent bond? (A), (B), (C), (D), or (E).
In this question, we want to determine which structure does not contain a coordinate covalent bond. We can do this by understanding the difference between conventional and coordinate covalent bonds.
A conventional covalent bond contains one or more valence electrons from each bonding atom or ion. A single covalent bond forms when there is one valence electron from each bonding atom. A double bond forms when there are two electrons from each bonding atom. And a triple bond is formed when three electrons from each bonding atom are shared.
Coordinate covalent bonds are an unusual type of covalent bond that contains valence electrons from a single bonding atom or ion. One bonding atom or ion effectively donates one or more electron pairs to another group. The donating species is often referred to as the Lewis base, and the acceptor is referred to as the Lewis acid. In Lewis diagrams, both conventional and coordinate covalent bonds are often represented in the same way, so it can be difficult to distinguish them. We can instead use dot-and-cross diagrams.
A dot-and-cross diagram assigns one bonding group dots and another crosses to determine if a bonding group is donating an electron pair and thus forming a coordinate covalent bond. For example, the valence electrons of species A have been drawn as dots, while those of species B are drawn as crosses. The diagram shows us that a coordinate covalent bond has formed, since the pair of electrons being shared were exclusively from the valence shell of species A. Let’s apply dot-and-cross diagrams to our answer choices to find which species does not contain a coordinate covalent bond.
Let’s start with answer choice (D) CO, or carbon monoxide, as it is the smallest species. We can assign crosses to carbon, and we know that carbon has four valence electrons. We can assign dots to oxygen, and we know that oxygen has six valence electrons available for bonding. From the Lewis structure, we can deduce that carbon will have a lone pair of electrons when bonding with oxygen to form this molecule.
We also know that these two atoms will form a triple bond, but carbon only has two more valence electrons available for bonding. The third pair of electrons shared between them will be donated by oxygen. Therefore, carbon monoxide has the dot-and-cross diagram shown. Because this molecule does contain a coordinate covalent bond with an electron pair donated by oxygen, we can eliminate answer choice (D).
Let’s now look at the dot-and-cross diagram for answer choice (C), called nitrous oxide. This molecule also contains a coordinate covalent bond, so it is not the answer to this question. Let’s have a look at answer choice (A), hydrogen peroxide. All three bonds are conventional covalent bonds, and so this molecule does not contain coordinate covalent bonds. Answer choice (A) is likely the correct answer, but let’s rule out (B) and (E) just to be sure.
Let’s have a look at the dot-and-cross diagram for answer choice (B), an ion called tetrachloroaluminate. This species does contain a coordinate covalent bond, and so we can eliminate answer choice (B). Answer choice (E), the ammonium ion, has the dot-and-cross diagram shown. This species does contain a coordinate covalent bond and thus can be eliminated.
Therefore, the option shown that does not contain a coordinate covalent bond is answer choice (A).
