Video Transcript
Fill in the blank. Group 15 elements can have
oxidation states that range from blank. (A) Minus five to plus three, (B)
minus three to plus five, (C) minus three to plus six, (D) minus two to plus five,
or (E) plus three to plus five.
In order to begin to answer this
question, let us first recall what we mean by oxidation state. The oxidation state indicates the
number of electrons that have been lost or gained from an atom. Oxidation states can be determined
by looking at the Lewis structure. When looking at the Lewis structure
for an element in group 15, such as phosphorus, we should note the element has five
valence electrons. The reason looking at the Lewis
structure is important is because it can help us to determine how many valence
electrons will be gained or lost by the element in order to reach eight valence
electrons, which will allow for chemical stability.
In order for chemical stability to
occur, an element in group 15 can gain up to three electrons. When electrons are gained by an
atom or ion, the process is called reduction. Let us take a look at what occurs
during reduction. When an electron is gained, the ion
has more electrons compared to protons and will therefore have a negative
charge. Phosphorus gains a maximum of three
electrons, in which case the charge would be minus three.
Note the set of eight electrons in
the Lewis structure of the outer energy level of the group 15 element. In this stable chemical state, no
other electrons can be gained. Since the lowest oxidation state is
therefore minus three, option (A), minus five to plus three; option (D), minus two
to plus five; and option (E), plus three to plus five, are incorrect.
Now that we have reviewed what
occurs to the oxidation state when electrons are gained, let us take a look at what
occurs when electrons are lost. When electrons are lost by an atom,
the process is known as oxidation. When an electron is lost, the ion
has fewer electrons compared to protons and will therefore have a positive
charge. If phosphorus were to lose one
electron, it would have a charge of plus one. When two electrons are lost, the
charge would be plus two. When three electrons are lost, the
charge would be plus three. If four electrons were lost, the
charge would be plus four. And when five electrons are lost,
the charge is plus five.
When looking at the Lewis structure
of phosphorus in the plus five state, we see that the electrons in the outer shell
have been lost. And the octet in the lower energy
level allows for the group 15 element to be chemically stable. Since the highest oxidation state
can be plus five, this means that option (C), minus three to plus six, is
incorrect. Therefore, the correct answer is
(B). Group 15 elements can have an
oxidation state that ranges from minus three to plus five.
