2Na(s) + Cl2Na(s) + Cl22 (g) (g) 2NaCl (s) 2NaCl (s)

Synthesizing an Synthesizing an IonicIonic Compound Compound

Explaining Salt Formation using the Explaining Salt Formation using the Born-HaberBorn-Haber Cycle Cycle

Na(s) + Cl2 NaCl H°f = -411 kJ/mol

Na(s) Na(g) H°f = 108 kJ/mol

Cl2 Cl(g) H°f = 122 kJ/mol

Na(g) Na+(g) + e- I1 = 496 kJ/mol

Cl(g) + e- Cl-(g) E = -349 kJ/mol

H = [H°f (NaCl)] - [H°f (Na+) + H°f (Cl-) + I1 + E]

H = -788 kJ/mol

Explaining Salt Formation using the Explaining Salt Formation using the Born-HaberBorn-Haber Cycle Cycle

Describing Electrostatic Attraction and Repulsion

E = kQ1Q2

d

E > 0 if the charges Q1 and Q2 have the same sign•Potential energy increases because the particles are repelling

E < 0 if the charges Q1 and Q2 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 = kQ1Q2

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 numberthe smaller the ion

Covalent Bonds are formed by shared pairs of electrons

H H+ H H H H

Cl Cl+ Cl Cl Cl Cl

Single Bonds

Double Bonds

O O+ C + O OC O OC

Triple Bonds

N N+ N N

Resonance Forms

OO

O OO

O

•Molecules with an odd number of electrons

•Molecules in which an atom has less than an octet

NO contains 5 + 6 = 11 electrons. No octet can be established

Though rare, these are most often encountered in compoundsof Born and Beryllium

B

FF

F

Exceptions to the Octet Rules

Molecules in which an atom has more than an octetThis is observed in compounds constructed from period 3 elements and beyond

PCl

Cl

Cl

Cl

Cl

3s 3p 3d

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 Cl Cl2 (g) H = 242 kJ

Bond Energies and the Enthalpy of Reactions

H = (bond energies of bonds broken) - (bond energies of bonds formed)

H = (bond energies of bonds broken) - (bond energies of bonds formed)Cl2(g) + H-CH3 H-Cl(g) + CH3Cl

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

H2 : Ediff = 2.1 -2.1 = 0

HCl: Ediff = 3.0 -2.1 = 0.9

Cl2 : Ediff = 3.0 - 3.0 = 0

note that LiF is ionic : Ediff = 4.0 - 1.0 = 3.0

H Cl

H Cl+ -

BH3 2.1-2.0 = .1

Ionic Character The bigger the electronegativity difference

the more ionic character. 1.4 has more ionic character than 1.2

noble gas configurations

Cl1-

Na1+

Cu1+

Sn2+

Isoelectronic O2-, Cl1-, Ne, Na1+, Mg2+

size trend

energy diagram page 366