Video Transcript
Oxygen forms a diatomic molecule
with a double covalent bond. The structural formula for diatomic
oxygen is shown. Why do oxygen atoms in this
molecule form more than one covalent bond? (A) There are six valence electrons
in the oxygen atom, so two electrons must be shared between atoms to produce stable
octets in their outer shells. (B) There are two valence electrons
in the oxygen atom, so sharing four electrons between atoms fully utilizes their
outer shells. (C) There are six valence electrons
in the oxygen atom, so four electrons must be shared between atoms to produce stable
octets in their outer shells. (D) There are two valence electrons
in the oxygen atom, so sharing two electrons between atoms fully utilizes their
outer shells. (E) There are four valence
electrons in the oxygen atom, so four electrons must be shared between atoms to
produce stable octets in their outer shells.
The first portion in all of our
answer choices has to do with the number of valence electrons in the oxygen
atom. Oxygen has six valence
electrons. So we can rule out answer choices
(B), (D), and (E). The next portion of our two
remaining answer choices has to do with the number of electrons that are shared
between atoms. Let’s get these incorrect answer
choices out of the way before we think about this part of the problem.
The valence shell of oxygen, as
well as many other atoms, holds a maximum of eight electrons. Eight valence electrons, or a full
octet, is a very stable electron configuration. It’s the same electron
configuration as a noble gas, such as neon. As this electron configuration is
so stable, atoms have a tendency to transfer or share electrons so that they can
have a full valence shell. This is known as the octet
rule. In an oxygen molecule, electrons
are shared to create a covalent bond. By doing this, both oxygen atoms
can have a full octet.
Both oxygen atoms in the oxygen
molecule are two electrons away from a full octet. So, if both oxygen atoms share two
electrons, both atoms will end up with a full octet. This means that there are four
electrons being shared in total. Two electrons are needed to create
one covalent bond. So, the four electrons shared by
the oxygen atom will create two covalent bonds.
So, the reason oxygen atoms in the
oxygen molecule form more than one covalent bond is answer choice (C): there are six
valence electrons in the oxygen atom, so four electrons must be shared between atoms
to produce stable octets in their outer shells.
Which of the following elements
also commonly forms a diatomic molecule with more than one covalent bond? (A) Be, (B) Ne, (C) C, (D) N, (E)
F.
As we saw in the last part of the
problem, atoms form covalent bonds so that they can share electrons to fill the
valence shell. So, let’s figure out how many
valence electrons each of our answer choices have. Beryllium has two valence
electrons, neon has eight, carbon has four valence electrons, nitrogen has five, and
atoms of fluorine have seven.
We can see that neon already has a
full valence shell, so it won’t form any covalent bonds. This is not the correct answer. Beryllium is an element in group
two of the periodic table. Beryllium can form some compounds
with covalent bonding such as beryllium hydride. But for the most part, beryllium
forms compounds with ionic bonds like the other elements in group two. So, answer choice (A) is also not
correct. This leaves us with answer choices
(C), (D), and (E).
Atoms of carbon need four more
electrons to have a full valence shell. So, carbon atoms tend to form four
covalent bonds. This is why carbon forms compounds
like methane and carbon dioxide. But we’re specifically interested
in diatomic molecules in this question. In order for there to be a diatomic
carbon molecule, there would have to be four bonds between the carbon atoms. But a quadruple bond is not
something that exists. So, answer choice (C) is not
correct.
Atoms of nitrogen have five valence
electrons. So, atoms of nitrogen tend to form
three bonds to have a full valence shell. This means there can be a diatomic
nitrogen molecule with three bonds between the nitrogen atoms. So, nitrogen is an element that can
form a diatomic molecule with more than one covalent bond. So answer choice (D) is the correct
answer, but let’s take a quick peek at answer choice (E).
Atoms of fluorine have seven
valence electrons, so these atoms can form one bond. So atoms of fluorine do tend to
form diatomic molecules, but this diatomic molecule only has one covalent bond, not
more than one. So, answer choice (E) is
incorrect.
Of the elements that we were given,
the only one that forms a diatomic molecule with more than one covalent bond was
answer choice (D) nitrogen.
