Q-1-1-22E - Organic Chemistry (Mcmurry)

Question

How many valence electrons does each of the following dietary trace elements have?

(a) Zinc (b) Iodine (c) Silicon (d) Iron

Step-by-Step Solution

Answer

(a) The number of valence electrons in zinc is 2.

(b) The number of valence electrons in iodine is 7.

(c) The number of valence electrons in silicon is 4

(d) The number of valence electrons in iron is 8.

Valence electrons

The valence electrons are the electrons that are present in the outermost shell of a neutral gaseous atom and take part in the formation of the chemical bond with other atoms.

 

(a) Electronic configuration of zinc

The atomic number of zinc is 30. The electronic configuration of zinc can be written as:

 $$\begin{gathered} \mathrm{Zn}-1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^{10} \mathrm{or} \\ \mathrm{Zn} -\left[\mathrm{Ar}\right]4{\mathrm{s}}^{2}3{\mathrm{d}}^{10} \end{gathered}$$

The number of the valence electron in the Zn is $2$ as the fourth shell is the outermost shell which has two electrons.

(b) The number of valence electrons in iodine

The atomic number of iodine is $53$and the electronic configuration is as follows 

  $$\begin{gathered} \mathrm{I}-1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^{10}4{\mathrm{p}}^{6}5{\mathrm{s}}^{2}4{\mathrm{d}}^{10}5{\mathrm{p}}^5 \mathrm{or} \\ \mathrm{I}-\left[\mathrm{Kr}\right]5{\mathrm{s}}^{2}4{\mathrm{d}}^{10}5{\mathrm{p}}^5 \end{gathered}$$

The valence electrons in iodine are $7$ as the fifth shell is the outermost shell which has seven electrons as the valence electrons.

(c) The number of valence electrons in silicon

The atomic number of silicon is 14 and the electronic configuration is as follows:

$$\begin{gathered} \mathrm{Si}-1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^2 \mathrm{or} \\ \mathrm{Si} -\left[\mathrm{Ne}\right]3{\mathrm{s}}^{2}3{\mathrm{p}}^2 \end{gathered}$$

 

The valence electron in silicon can be calculated as the number of electrons in the third shell. As the third shell is the outermost shell, so the valence electron in silicon are four.

(d) The number of valence electrons in iron

The atomic number of iron is $26$ and its electronic configuration is as follows:

  $$\begin{gathered} \mathrm{Fe}-1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^6 \mathrm{or} \\ \mathrm{Fe} -\left[\mathrm{Ar}\right]4{\mathrm{s}}^{2}3{\mathrm{d}}^6 \end{gathered}$$

 

The total number of valence electrons in iron is 8 as the outermost shells have in total $2+6=8$ valence electrons together in 4s and 3d- subshells.