Unformatted text preview: of H-atoms times two. (Note the
exceptions for Be and B.)
3. Determine the number of shared electrons, S . S=N−A
The number of bond pairs is S /2.
4. Start with a plausible skeleton structure. This is a representation of the order in which atoms are bonded together. The
skeleton structure consists of one or more central atoms with
the other terminal atoms bonded to the central atom(s).
5. Place the bond pairs in the skeleton structure, starting with
one bond pair between each pair of atoms. If bond pairs remain, form double or triple bonds.
If the number of bond pairs is less than the number needed
to bond all atoms, then S is increased to the number of elecGChem I 9.9 trons needed. This generally indicates that the central atom
displays expanded valence.
6. Determine the number of remaining valence electrons, A − S .
Place these electrons as lone pairs, starting with the terminal atoms to complete the octets (exceptions!). If electrons
are left over, place them on the central atom (expanded valence...
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