Key Terms
Cation
Atom loses electrons; positive charge. Anion: atom gains electrons; negative charge.
Example
CO2 could be drawn three ways. The structure with C in center and two double bonds gives all formal charges of zero.
Main group cations
Lose all valence electrons; take on noble gas config of the preceding element.
Transition metals
Lose s electrons FIRST, then d electrons.
Anions
Gain electrons to fill valence shell to next noble gas config.
Covalent bond
Atoms SHARE electrons instead of transferring them. Forms between atoms with similar electronegativities (usually nonmet
Bond length
Distance at which potential energy is minimized. Bond formation releases energy (exothermic).
Pure (nonpolar) covalent
Identical atoms share equally. ΔEN = 0.
Electronegativity
How strongly an atom attracts electrons in a bond.
Pauling scale
0 to 4. Fluorine is highest at 4.0.
Single bond
One shared pair Double bond: two shared pairs (C=O in formaldehyde) Triple bond: three shared pairs (N in N2; C in CO an
Examples
PCl5 (10 electrons on P), SF6 (12 electrons on S), XeF4 (12 electrons on Xe including lone pairs)
Formula
Formal charge = valence electrons - lone pair electrons - (1/2 bonding electrons)
Or equivalently
Formal charge = valence electrons - (nonbonding electrons) - (number of bonds)
Evidence for resonance
Bond lengths are identical where they should differ if only one structure were real. Example: NO2- has two N-O bonds of