Chemistry 100 Chapter 8. Chemical Bonding Basic Concepts. The Valance Electrons. When atoms interact to form chemical bonds, only the outer (valance) electrons take part. Need a tool for keeping track of valence electrons, e.g., The Lewis dot symbol 1 v.E. 7 v.E’s
Chemical Bonding Basic Concepts
1 v.E. 7 v.E’s
2 Na (s) + Cl2 (g) ® 2 NaCl (s)
(g) ® Na+ (g) + e- (ionizes, loses e-)
KCl (s) K+ (g) + Cl- (g) H = 718 kJ/mol
Determined using a thermochemical cycle -
the Born-Haber cycle (a Hess’s Law application)
H2 ® H-H, F2® F-F, Cl2 Cl-Cl
lone pairs (non bonding)
Note both Cl2 and F2 satisfy their valence shell requirements by the formation of a single bond.
Valence shell requirements are satisfied by the formation of a double bond.
Electronegativity is related to the electron affinity and the ionization energy.
All remaining electrons are assigned to the central atom. Atoms in the 3rd or higher row can have more than eight electrons around them.
BF3 + NH3® BF3NH3
2 NO2 (g) ⇄ N2O4 (g) Keq = 210
Reason - elements in this category can use the energetically low-lying d orbitals to accommodate extra electrons
With the possibility of using the low lying d-orbitals on the Cl atom to accommodate extra electron pairs, we may write other Lewis structures
H2 (g) ® H (g) + H (g) DH° = 436.4 kJ
Cl2 (g) ® Cl (g) + Cl (g) DH° = 242 kJ
CO2 (g) ® C (g) + 2 O (g) DH = 745 kJ
CH4 (g) ® C(g) + 4 H (g) DH° = 1650 kJ
H2O (g) ® H (g) + OH (g) DH° = 502 kJ/mol H2O
HO (g) ® H (g) + O (g) DH= 427 kJ/mol H2O