Video Transcript
During a chemical reaction, a
chlorine atom gains one electron from another atom as shown in the diagram. What is formed when the chlorine
atom gains an electron?
The images show two electron shell
diagrams. The first electron shell diagram is
for a chlorine atom. The second electron shell diagram
is for the same atom after it has gained one electron. We are asked what is formed when
the chlorine atom gains an electron. Let’s start by reminding ourselves
what a chlorine atom is.
Chlorine is a nonmetal element, it
is found on the periodic table in group 17, and chlorine has an atomic number of
17. This means there are 17 positively
charged protons in the nucleus of an atom of chlorine. In an atom, the number of protons
is equal to the number of electrons. Electrons are negatively charged
particles, which are found outside the nucleus. Since an atom of chlorine has 17
protons, it must have 17 electrons to be electrically neutral. These 17 electrons are arranged
into electron shells, which are also called energy levels.
There are two electrons in energy
level K. Energy level K is the closest shell
to the nucleus, and it is lowest in energy. Then, there are eight electrons in
energy level L. The final seven electrons are found
in energy level M. Chlorine is more stable when it has
eight electrons in its outer electron shell, which is energy level M. So, chlorine atoms do not exist on
their own but react with other atoms to gain one electron or take one electron from
another atom. In this way, chlorine atoms get one
extra electron and end up with eight electrons in energy level M. This configuration is more
stable.
When a chlorine atom gains an
electron, it no longer has the same number of protons as electrons. Instead, it now has 17 protons and
18 electrons. It has one extra negatively charged
electron, and so it is no longer neutral. It has a negative charge. We call an atom which has gained or
lost electrons an ion. So, ions are charged particles
since their number of protons and number of electrons are not equal.
Finally, what is formed when the
chlorine atom gains an electron? A negatively charged ion is
formed.
