2Na(s) + Cl 2 (g)  2NaCl (s) Synthesizing an Ionic Compound

Explaining Salt Formation using the Born-Haber Cycle

Na(s) +  Cl 2  NaCl  H° f = -411 kJ/mol Na(s)  Na(g)  H° f = 108 kJ/mol  Cl 2  Cl(g)  H° f = 122 kJ/mol Na(g)  Na + (g) + e - I 1 = 496 kJ/mol Cl(g) + e -  Cl - (g) E = -349 kJ/mol  H = [  H° f (NaCl)] - [  H° f (Na + ) +  H° f (Cl - ) + I 1 + E]  H = -788 kJ/mol Explaining Salt Formation using the Born-Haber Cycle

Describing Electrostatic Attraction and Repulsion E = k Q1Q2Q1Q2 d E > 0 if the charges Q 1 and Q 2 have the same sign Potential energy increases because the particles are repelling E < 0 if the charges Q 1 and Q 2 have different signs Potential energy decreases because the particles are attracting

The lattice energy of NaCl is the result of all the electrostatic repulsions and attractions. Because the attractions outweigh the repulsions, the lattice energy is positive and large E = k Q1Q2Q1Q2 d

Sizes of Ions size depends upon nuclear charge size depends upon numbers of electrons size depends upon orbitals in which the outer electrons reside

Within an Isoelectric Series, the higher the atomic number the smaller the ion

Covalent Bonds are formed by shared pairs of electrons H H + HH   HH Cl +   Single Bonds Double Bonds O O + C +  O O C O O C  Triple Bonds N N +  N N

Resonance Forms O O O  O O O

Molecules with an odd number of electrons Molecules in which an atom has less than an octet NO contains = 11 electrons. No octet can be established Though rare, these are most often encountered in compounds of Born and Beryllium B F F F Exceptions to the Octet Rules

Molecules in which an atom has more than an octet This is observed in compounds constructed from period 3 elements and beyond P Cl 3s 3p3d Exceptions to the Octet Rules

Strengths of Covalent Bonds Bond dissociation Energy (Bond Energy): is the enthalpy change (  H) required to break a particular bond in a mole of gaseous substance (g)  Cl 2 (g)  H = 242 kJ Bond Energies and the Enthalpy of Reactions  H =  (bond energies of bonds broken) -  (bond energies of bonds formed)

Cl 2(g) + H-CH 3  H-Cl(g) + CH 3 Cl  H = [(Cl-Cl) + 4(H-C)] - [(Cl-Cl) + 3(H-C) + (Cl-C)]  H = [242 kJ+4(413 kJ)]-[431 kJ + 4(413kJ) + (328)] = -104 kJ

Bond Strength and Bond Length

Electronegativity and Bond Polarity “the ability of an atom in a molecule to attract electrons to itself”

Electronegativity and Bond Polarity H 2 : E diff = = 0 HCl: E diff = = 0.9 Cl 2 : E diff = = 0 note that LiF is ionic : E diff = = 3.0 H Cl H ++ -- BH =.1

Ionic Character 4 The bigger the electronegativity difference the more ionic character has more ionic character than 1.2

noble gas configurations 4 Cl 1- 4 Na 1+ 4 Cu 1+ 4 Sn 2+

Isoelectronic 4 O 2-, Cl 1-, Ne, Na 1+, Mg 2+ 4 size trend

energy diagram page 366