Chemical Bonding I www.chem.hawaii.edu/Bil301/welcome.html CHEMISTRY 161 Chapter 9 Chemical Bonding I www.chem.hawaii.edu/Bil301/welcome.html

Periodic Table of the Elements ns2np6 ns1 ns2 chemical reactivity - valence electrons

THE OCTET RULE ns2np6 atoms combine to form compounds in an attempt to obtain a stable noble gas electron configuration ns2np6 isoelectronic

A + B → AB 1. ELECTRON FULLY TRANSFERED IONIC BONDING NaCl 2. ELECTRON SHARING COVALENT BONDING HCl

represents one valence electron LEWIS MODEL OF BONDING LEWIS DOT SYMBOL DOT represents one valence electron H. Gilbert Lewis (1875-1946)

. . . . . . . . . . with the exception of He, the main group number represents number of ‘dots’

IONIC BONDING Na electron transfer Ne core implied in symbol 1s22s22p63s1 Lewis Symbol

Cl Na Ne core implied in symbol 1s22s22p63s23p5 1s22s22p63s1 Lewis Symbol

IONIC BONDING  Cl Cl Na Na+ the formation of ionic bonds is represented in terms of Lewis symbols Cl Cl Na  Na+ 1s22s22p63s23p6 1s22s22p6 the loss or gain of electrons(dots) until both species have reached an octet of electrons

represents one orbital Cl Cl [Ne] 3s23p6 represents one orbital (Pauli: 2 electrons)

ions stack together in regular crystalline structures electrostatic interaction ionic solids typically 1. high melting and boiling points 2. brittle 3. form electrolyte solutions if they dissolve in water

Li(s) + ½ F2(g) → LiF(s) enthalpy of formation lattice energy Li+(g) + F-(g) → LiF(s) Hess’s Law enthalpy is a state function Born-Haber Cycle

Li(s) + ½ F2(g) → LiF(s) Li+(g) + F-(g) Li(g) + F(g) Li(s) + ½ F2(g) 5 ΔHoR= Σ ΔHoi i=1 ΔHo4 ΔHo3 ΔHo5 Li(g) + F(g) ΔHo1 ΔHo2 ΔHoR Li(s) + ½ F2(g) LiF(s)

Mg(s) + ½ O2(g) → MgO(s) Mg2+(g) + O2-(g) Mg+(g) + O-(g) Mg(g) + O(g) ΔHo6 7 ΔHo5 ΔHoR= Σ ΔHoi i=1 Mg+(g) + O-(g) ΔHo7 ΔHo3 ΔHo4 Mg(g) + O(g) ΔHo1 ΔHo2 ΔHoR MgO(s) Mg(s) + ½ O2(g)

Lattice Energy of Ionic Compounds SUMMARY Lewis Dot Octett Rule Lattice Energy of Ionic Compounds 600 – 4000 kJmol-1

Homework Chapter 9 pages 329-337, problem sets