Question

Draw Lewis electron dot diagrams for the following species:

(a) methane;

(b) carbon dioxide;

(c) phosphorus trichloride;

(d) perchlorate ion.

Short answer

The Lewis electron dot diagrams for the following species:

Step-by-step solution

Step 1:

Lewis dot structures represent the valence electrons of the given atoms.
In order to create the most plausible distribution of electrons among the atoms in a given particle, one has to

1. first create the $\mathrm{\pi }$bonds:
2. then assign the remaining electrons to the atoms (as lone pairs) in decreasing order by electronegativity:
3. finally, check for atoms (except$\mathrm{H}$ ) with less than four valences (if found any: rearrange the neighboring electron pairs to the sufficient number of$\mathrm{\pi }$ bonds)

Lewis structures are not necessarily meant to represent the real distances and angles between atoms but the symbols may be arranged in a way that shows some properties of the real structure. If not, bond angles are generally rendered as right angles.
Electron pairs are represented with "double dots" or lines - unpaired electrons always have the corresponding number of dots.

Step 2:

(a) Methane -${\mathrm{CH}}_4$

The image below depicts the structure. This molecule follows the above rules plain and simple: there are 8 electrons in total, four on behalf of the carbon, four more "belonging" to the hydrogen atoms.

Step 3:

b) Carbon dioxide -${\mathrm{CH}}_2$

In this case, 16 electrons are in total. This structure needed some adjustment: after the bonds and the lone pairs were added, the valency on carbon was only two and the oxygens had three lone pairs each. The situation was perfect to create two $\mathrm{\pi }$bonds instead.

Step 4:

(c) Phosphorus trichloride $-{\mathrm{PCl}}_{3\text{'}}$