Lewis StructuresElectronegativityElectronegativityBond PolarityBond PolarityBond PolarityWriting Lewis StructuresWriting Lewis StructuresWriting Lewis StructuresFormal ChargesFormal ChargesChapter 8 1Lewis StructuresA Lewis structure is a combination of Lewis symbols that represents the formation of covalent bonds between atoms.Chapter 8 2ElectronegativityElectronegativity is a measure of the ability of atoms in a molecule to attract electrons to themselves.ElectronegativityChapter 8 3Chapter 8 4Bond PolarityIn a polar covalent bond, the electrons are shared unequally.In a nonpolar covalent bond, there is an equal sharing of electrons.Ionic bonds form between atoms having large electronegativity differences.Chapter 8 5Bond PolarityWhen two atoms share electrons unequally, a dipole results.The dipole moment (μ) is a measure of the magnitude of the dipole:where Q is the magnitude of the two charges and r is the distance between them. m=QrBond PolarityChapter 8 6Chapter 8 7Writing Lewis Structures1. Find the sum of valence electrons of all atoms in the molecule or polyatomic ion.If it is an anion, add one electron for each negative charge.If it is a cation, subtract one electron for each positive charge.Chapter 8 8Writing Lewis Structures2. The central atom is the least electronegative element that isn’t hydrogen; connect the outer atoms to it by single bonds.3. Fill the octets of the outer atoms with lone pairs.4. Fill the octet of the central atom with lone pairs.Chapter 8 9Writing Lewis Structures5. If the number of electrons runs out before the central atom has an octet, form multiple bonds until it does.Chapter 8 10Formal ChargesWhen more than one different Lewis structure can be drawn, formal charges are used to decide which is the best.For each atom in the structure, count the electrons in lone pairs and half the electrons it shares with other atoms, then subtract this number from the number of valence electrons that atom has alone.Chapter 8 11Formal ChargesThe best Lewis structure is usually the one with the fewest nonzero formal charges or puts a negative charge on the most electronegative