Video Transcript
Which of the following is correct
for a nonmetal atom when it gains electrons? (A) Its outer electron shell is
filled with electrons. (B) It changes into a negative
ion. (C) The number of negative charges
in the ion is equal to the number of electrons gained. (D) The number of electrons in the
ion formed is more than the number of protons in it. (E) All of the answers are
correct.
The question talks about a nonmetal
atom. We know that in the center of any
atom is the nucleus. The nucleus contains positively
charged particles called protons. And it contains neutral particles
called neutrons. Outside the nucleus are negatively
charged particles called electrons. Electrons are arranged into
different energy levels, or shells, each with different energies.
Nonmetal atoms tend to have more
than four electrons in their outer shell, which is the reason why nonmetals gain
electrons when they react, as we shall understand in a moment. For example, here is the electronic
configuration of an atom of the nonmetal oxygen. The nucleus has eight protons,
since this is the atomic number of oxygen. We aren’t interested in the number
of neutrons in this question. So we won’t draw them in. An atom is neutral overall. So the number of protons must equal
the number of electrons. And so we can deduce that this atom
must have eight electrons.
These eight electrons are arranged
in the energy levels as follows. There are two electrons in energy
level K and six electrons in energy level L. Energy level L can hold a maximum
of eight electrons. We can see that energy level L is
not yet full.
When a nonmetal atom reacts, it
tends to gain electrons. Why is this? For any atom to be stable, their
outer energy level should ideally be full. Since oxygen’s outer energy level
contains six electrons, it requires less energy for an oxygen atom to gain two
electrons to fill this shell than to lose all six electrons in this shell. So, oxygen atoms tend to gain two
electrons when they react to get a full outer shell which is very stable. Thus, we can see that answer (A) —
its outer electron shell is filled with electrons — is a true statement for a
nonmetal atom gaining electrons.
When a neutral atom gains
electrons, it becomes negatively charged. We can see that there are eight
positive protons and 10 negative electrons now. The number of protons and electrons
is no longer equal. The atom has changed into a
negative ion. (B) — it changes into a negative
ion — is also a true statement.
We can see that for this oxygen
ion, two negative electrons were gained. So the ion has an overall charge of
two minus. In other words, the number of
negative charges in the ion is equal to the number of electrons gained. So, statement (C) is also true.
Since a negative ion has more
electrons than protons, we can conclude that statement (D) is also true. The number of electrons in the ion
formed is more than the number of protons in it.
Since statements (A), (B), (C), and
(D) are all true statements for a nonmetal atom gaining electrons, we can conclude
that the correct answer for this question is (E). All of the answers are correct.
