Each molecule listed contains an expanded octet (10 or 12 electrons) around the central atom. Write the Lewis structure for each molecule.
Here, we are going to write the lewis structure for the given molecules.
The Lewis dot structure provide a picture of bonding in molecules and ions in terms of the shared pairs of electrons and the octet rule. While such a picture may not explain the bonding and behaviour of a molecule completely, it does help in understanding the formation and properties of a molecule to a large extent. Writing of Lewis dot structures of molecules is, therefore, very useful.
There are certain rules to draw the Lewis structure. They are:The total number of electrons required for writing the structures are obtained by adding the valence electrons of the combining atoms. For anions, each negative charge would mean addition of one electron. For cations each positive charge would result in subtraction of one electron from the total number of valence electrons.Knowing the chemical symbols of the combining atoms and having knowledge of the skeletal structure of the compound, it is easy to distribute the total number of electrons as bonding shared pairs between the atoms in proportion to the total bonds.In general, the least electronegative atom occupies the central position in the molecule/ion.After accounting for the shared pairs of electrons for single bonds, the remaining electron pairs are either utilized for multiple bonding or remain as the lone pairs. The basic requirement being that each bonded atom gets an octet of electrons.
But, in a number of compounds of elements in and beyond the third period of the periodic table, there are more than eight valence electrons around central atom. This is termed as the expanded octet. The octet rule does not apply in such cases.
Number of valence electrons in P = 5
Number of valence electrons in F = 7
Total number of valence electrons in PF5 = 5 + (7 x 5) = 40
Here, phosphorus(P) shares its 5 valence electrons with the five fluorine atoms and as a result expands its octet to 10 electrons. The lewis structure for the molecule is: