The charge of an ion allows us to determine
the number of electrons.
We know that the number of protons for the
atom of a given element never changes and
is found on the periodic table as the atomic
number.
The charge of an ion is due to the unequal
number of protons and electrons.
To determine the number of electrons, we subtract
the overall charge of the ion from the number
of protons.
Let’s apply that mathematical formula.
Determine the number of protons and electrons
in the following ions.
Potassium or capital K charge of positive
one and oxide or capital O charge of negative
two.
Pause the video to get the answers.
We need the number of protons and potassium
has an atomic number of nineteen and it has
nineteen protons.
And oxygen has an atomic number of eight and
thus has eight protons.
For the potassium cation, the number of electrons
is nineteen minus the charge of plus one which
is eighteen electrons.
This makes sense since cations have more protons
than electrons.
For oxide, we subtract the charge of negative
two from eight to obtain ten electrons.
This also makes sense since anions have more
electrons than protons.
It is actually no coincidence that the number
of electrons in those ions equals the number
of electrons in the nearest noble gas.
Oxide anion had ten electrons like neon and
potassium cation had eighteen electrons like
argon.
Main group atoms that are non-metals will
gain (up to three) electrons to obtain the
same number of electrons as the nearest noble
gas and main group metals tend to lose electrons
to obtain the same number of electrons as
the nearest noble gas.
Thus, there are series of monoatomic ions
that have the same number of electrons as
noble gases.
A series of ions that have the same number
of electrons is known as isoelectronic.
That means we will see main group monoatomic
ions with ten, eighteen, thirty-six and fifty-four
electrons.
