<P> Once all lone pairs are placed, atoms, (especially the central atoms,) may not have an octet of electrons . In this case, the atoms must form a double bond; a lone pair of electrons is moved to form a second bond between the two atoms . As the bonding pair is shared between the two atoms, the atom that originally had the lone pair still has an octet; the other atom now has two more electrons in its valence shell . </P> <P> Lewis structures for polyatomic ions may be drawn by the same method . When counting electrons, negative ions should have extra electrons placed in their Lewis structures; positive ions should have fewer electrons than an uncharged molecule . </P> <P> When the Lewis structure of an ion is written, the entire structure is placed in brackets, and the charge is written as a superscript on the upper right, outside the brackets . </P> <P> A simpler method has been proposed for constructing Lewis structures, eliminating the need for electron counting: the atoms are drawn showing the valence electrons; bonds are then formed by pairing up valence electrons of the atoms involved in the bond - making process, and anions and cations are formed by adding or removing electrons to / from the appropriate atoms . </P>

What do the electron dot structures of elements in the same group have in common