Question

The atomic numbers of Al and Cl are 13 and 17 respectively. What will be the number of electrons in $A{l}^{3+}$ and $C{l}^{-}$ respectively?

Answer 1

Hint: The charge on the ion describes the number of electrons added or subtracted from the atomic number of its corresponding atom The positive charge on the cation tells that the electrons have decreased from the ground state configuration and the negative charge on the anion tells that the electrons have increased from the ground state configuration.

Complete step by step answer:
-We know that the cation is the positively charged ion. The number of protons is more than
the number of electrons in the cation and the anion is the negatively charged ion. The number of protons is less than the number of electrons in the anion.
-Now, we are given that the atomic number of Al is 13.
-Let’s see the electronic configuration of Al in its ground state.
$$\text{Al (G}\text{.S}\text{.): }1s^{2}2s^{2}2p^{6}3s^{2}3p^1$$
-Thus, we can see that a total 13 electrons are present here.
Now, $A{l}^{3+}$ suggests that three electrons have been removed from the ground state
-electronic configuration of Aluminum. So, its electronic configuration will be:
$$A{l}^{3+}:1s^{2}2s^{2}2p^6$$
- Thus, in this configuration we can count that there are total of 2+2+6=10 electrons present
in this configuration. So, $A{l}^{3+}$ has 10 electrons.
- Atomic number of Chlorine is 17.
So, the ground state electronic configuration of chlorine will be:
$$Cl\text{ :1}{\text{s}}^{2}2s^{2}2p^{6}3s^{2}3p^5$$
-Here, a total of 17 electrons are present.
-Now, $C{l}^{-}$ suggests that this species has one more electron than its ground state
electronic configuration. So, the electronic configuration of $C{l}^{-}$ will be:
$$C{l}^{-}:1s^{2}2s^{2}2p^{6}3s^{2}3p^6$$
Here, we can count that a total of 18 electrons are present here.
-These atoms have achieved the atomic numbers of the noble gases. $A{l}^{3+}$ has the
electronic configuration of the noble gas, neon (Ne). $C{l}^{-}$ has the electronic
configuration of the noble gas, argon (Ar).
-So, the number of electrons in $A{l}^{3+}$ and $C{l}^{-}$ will be 10 and 18 respectively.

Note:
It is the tendency of an ion to achieve the nearest noble gas configuration to attain the
maximum stability. Remember that a positive charge on an atom suggests that it has lost
some electrons. When negative charge is there on atom, it means that it has gained some
electrons.