Electrons dot structures are also called Lewis structure. In this model, the valence electrons of each atom are represented and how the bond between them occurs, after all, the stability of the atom is in its valence shell.
To determine the Lewis structure of each molecule, we must perform the following steps.
Step 1 - Determine the number of valence electrons of each atom.
Step 2 - Determine the position of atoms in the structure: the central atom is always the one with the lowest electronegativity, and monovalent atoms (which make only one bond) are positioned around the central atom.
Step 3 - Share the electron pairs of atoms around the central atom, completing the octet.
Step 4 - If electrons are missing to complete the octet, double or triple bonds must be made.
As an example, let's represent the Lewis structures for methane, with molecular formula CH4:
C has 4 electrons in its valence shell.
H has 1 electron in its valence shell.
So we represent both in this way:
C with 4 dots around it and H with 1 dot. But we have H atoms of hidrogen. The hydrogen atoms will be around the central atom (C) as they are monovalent:
Now let's share the electrons:
How to do an electronic distribution:
To make the electronic distribution of an atom, we must distribute its total amount of electrons in its energy sublevels, respecting the Linus Pauling diagram, filling in the lower energy sublevels first, and as you complete them in their maximum quantities, proceed to the following sublevels and so on.
Example: C
C has 6 electrons (we know that because we find it on the periodic table, if the atom is neutral, like it is in this case, it has the same number of electrons as its atomic number.)
The electronic distribution of C is:
1s² 2s² 2p²
The quantity of electrons on C valence shell, which are the quantity of dots you will draw, it is the sum of the numbers of the last level (in this case, the level is 2) and we have 2s² 2p², so 2+2 is 4.