A sports-drink manufacturer is writing a technical data sheet explaining the electrolyte ions in a new product: sodium ions, Na^+, and chloride ions, Cl^-. Sodium has proton number 11 and chlorine has proton number 17. (a) Write the electronic configuration of a sodium atom and…

Answer: ((a)) sodium atom: 2,8,1; chlorine atom: 2,8,7 ((b)) Na+ ion: 2,8 (loses its single outer electron); Cl- ion: 2,8,8 (gains one electron into its outer shell) ((c)) (i) neon, which also has the configuration 2,8; (ii) argon, which also has the configuration 2,8,8 ((d)) Magnesium is in Group II. Its electronic configuration is 2,8,2, so it has 2 electrons in its outer shell, and the number of outer-shell electrons equals the group number for Groups I to VII.. Part (a): Electronic configuration of the atoms Electrons fill shells starting from the innermost shell, with a maximum of 2 in the first shell and up to 8 in the second and third shells (for these proton numbers). - Sodium (proton number…

IGCSE Chemistry 0620: Electronic Configuration of Atoms, Ions and Noble Gases

A sports-drink manufacturer is writing a technical data sheet explaining the electrolyte ions in a new product: sodium ions, $\text{Na}^+$ , and chloride ions, $\text{Cl}^-$ . Sodium has proton number 11 and chlorine has proton number 17.

(a) Write the electronic configuration of a sodium atom and of a chlorine atom. [2]

(b) Write the electronic configuration of a $\text{Na}^+$ ion and of a $\text{Cl}^-$ ion. [2]

(c) State the name of the noble gas that has the same electronic configuration as (i) the $\text{Na}^+$ ion, and (ii) the $\text{Cl}^-$ ion. [2]

(d) Magnesium, proton number 12, is also used in some sports-drink formulations, as $\text{Mg}^{2+}$ . Use the electronic configuration of a magnesium atom to state which group of the Periodic Table magnesium is in, and explain your reasoning. [2]

Part (a): Electronic configuration of the atoms

Electrons fill shells starting from the innermost shell, with a maximum of 2 in the first shell and up to 8 in the second and third shells (for these proton numbers).

Sodium (proton number $11$ ): $2, 8, 1$
Chlorine (proton number $17$ ): $2, 8, 7$

Part (b): Electronic configuration of the ions

Forming an ion only changes the number of electrons. The number of protons and neutrons stays the same.

$\text{Na}^+$ forms when a sodium atom loses its single outer-shell electron: $2, 8, 1 \rightarrow 2, 8$
$\text{Cl}^-$ forms when a chlorine atom gains one electron into its outer shell: $2, 8, 7 \rightarrow 2, 8, 8$

Part (c): Matching ions to noble gases

$\text{Na}^+$ has configuration $2, 8$ (10 electrons), which is the same as an atom of neon.
$\text{Cl}^-$ has configuration $2, 8, 8$ (18 electrons), which is the same as an atom of argon.

Note that the two ions do not share the same noble gas configuration as each other. $\text{Na}^+$ matches neon, while $\text{Cl}^-$ matches argon, because they started from atoms with different numbers of electron shells.

Part (d): Magnesium’s group from its electronic configuration

Magnesium (proton number $12$ ) has electronic configuration $2, 8, 2$ .

The number of electrons in the outer shell is $2$ . For Groups I to VII, the number of outer-shell electrons is equal to the group number, so magnesium is in Group II.

Final answers

(a) Sodium atom: $2,8,1$ ; chlorine atom: $2,8,7$ .
(b) $\text{Na}^+$ : $2,8$ ; $\text{Cl}^-$ : $2,8,8$ .
(c) (i) neon; (ii) argon.
(d) Magnesium is in $\boxed{\text{Group II}}$ , since it has 2 outer-shell electrons.