Explain: Lewis dot representation.

(N/A) Number of total electrons in a neutral molecule: The total number of electrons required for writing the structures is obtained by adding the valence electrons of the combining atoms. For example,in the $CH_{4}$ molecule,there are eight valence electrons available for bonding ($4$ from carbon and $4$ from the four hydrogen atoms).
Number of electrons in a negative ion: Each negative charge means the addition of one electron to the total number of valence electrons. e.g.,For the $CO_{3}^{2-}$ ion,in Lewis representation,there are a total of $24$ electrons,in which $4$ $e^{-}$ are from one carbon,$18$ $e^{-}$ are from three oxygen atoms,and $2$ additional $e^{-}$ are from the two negative charges.
$(\text{Number of electrons in negative ion}) = (\text{Total valence electrons of all atoms}) + (\text{Number of negative charges})$
Number of electrons in a positive ion:
$(\text{Number of electrons in positive ion}) = (\text{Total valence electrons of all atoms}) - (\text{Number of positive charges})$
e.g.,$(\text{Total electrons in } NH_{4}^{+}) = (\text{Valence electrons of } N \text{ and } 4 H) - 1$
$= (5 + 4) - 1 = 8$
Distribution of electrons: Knowing the chemical symbols of the combining atoms and having knowledge of the skeletal structure of the compound (known or guessed intelligently),it is easy to distribute the total number of electrons as bonding shared pairs between the atoms in proportion to the total bonds.
Position of electrons: After accounting for the shared pairs of electrons for single bonds,the remaining electron pairs are either utilized for multiple bonding or remain as lone pairs. The basic requirement is that each bonded atom gets an octet of electrons.