Question

What is the charge on the chromium ion in the ionic compound that has the formula $Cr{}_2O{}_3$ ?

Answer 1

Hint : To find the number of electrons, we have to take atomic number under consideration. The number of electrons is equal to atomic number. For example; chlorine has $17$ electrons because the atomic number of chlorine is $17$ . The loss or gain electrons will depend on these $17$ electrons that are configured around the nucleus.

Complete Step By Step Answer:
Atoms have a tendency to lose or gain electrons in order to be stable. When the electrons have gained or lost some electrons, charge associates with them since their electron and proton numbers are not balanced anymore. To determine what happens to the electrons an atom has, it all has to do with the number of electrons in the valence shell of an atom.
The given compound has a net charge of zero
$2 \times Cr + O = 0$
Oxygen has a charge of $- 2$ so,
$2 \times Cr + 3( - 2) = 0$
$2 \times Cr + - 6 = 0$
Adding six on both sides
$2 \times Cr + - 6 + 6 = 0 + 6$
Now, let us divide by two on both sides.
22 \times Cr = + 62 \\\ Cr = \dfrac{{62}}{{22}} \\\ Cr = + 3 \\\
Hence the charge present on chromium ion in the ionic compound is $+ 3$ .

Note :
When there is loss or gain of electrons takes place to make an atom gain more stability. The moment this process takes place it is no longer called an atom but an ion. Electrons are being ordered into rings around the nucleus of the atom. The first ring is full and has two electrons. The other ring has eight electrons. Once the valence shell is full it can neither gain nor lose electrons.