CHEM 1311 Lecture Notes - Lecture 4: Ionic Compound, Ionic Bonding, Noble Gas
Chapters 5.1-5.3 and 6: Chemical Bonding I
Focus of this section: Covalent and Ionic bonding
Lewis symbols
Lewis structures
Lewis Dot Symbols:
• Gilbert Lewis (1875-1946): American Chemist
-- chemical bonding, thermodynamics, acids and bases,
spectroscopy
-- suggested that atoms combine with other atoms in
order to obtain more stable valence e– configuration
(isoelectronic to closest noble gas)
-- valence e– interact between atoms
• Lewis Symbol: represents valence e– of atom as dots around
the atomic symbol [each dot = valence e–]
-- Most useful for main-group elements
= # dots = group number!
-- don’t pair up dots until necessary
BeBe not N
-- for p-subshell elements: # unpaired = # bonds that
atom can form (goal noble gas config.)
-- for ions, add or remove dots to reflect final # valence e–
(goal noble gas config.)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Write Lewis dot symbols for the following:
Ca O2–
O K+
Xe
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Ionic Bonding:
• atoms to left of periodic table (IA and 2A): form cations
-- low IE and EA
• atoms to right of periodic table (esp. 6A and 7A): anions
-- high IE and EA
• Ionic bonding: electrostatic attractions between oppositely
charged ions
I
K K+e–
+
e–
+I
–
KI
+K++I
–
• Energy changes for formation of ionic compounds:
-- formation of K+ requires energy input (IE)--unfavorable
-- formation of I– favorable (EA)
-- combine: IE + EA > 0 (requires energy input)
(+) (–)
I
K K+e–
+
e–
+I
–
KI
+K++I
–
• HOWEVER, formation of ionic compounds (bringing anions
and cations together) typically VERY favorable (i.e.,
releases energy)
-- compensates for unfavorable steps
• Lattice Energy: amount of energy required to completely
convert 1 mole of a solid ionic compound to the
constituent ions in gas phase:
KI (s) → K+ (g) + I– (g) LE = +632 kJ mol–1
-- the greater LE, the stronger the interactions in the ionic
substance
LE = k Q1 Q2 Q1, Q2 = charges
d2 d = distance between
ion centers
k = 8.99x109 J m C–2
-- LE increases as: -- charges increase
-- size of ions decrease (d)
Document Summary
Focus of this section: covalent and ionic bonding. Lewis dot symbols: gilbert lewis (1875-1946): american chemist. - suggested that atoms combine with other atoms in spectroscopy order to obtain more stable valence e configuration (isoelectronic to closest noble gas) - valence e interact between atoms: lewis symbol: represents valence e of atom as dots around the atomic symbol. - for p-subshell elements: # unpaired = # bonds that atom can form (goal noble gas config. ) - for ions, add or remove dots to reflect final # valence e . Ionic bonding: atoms to left of periodic table (ia and 2a): form cations, atoms to right of periodic table (esp. 6a and 7a): anions: ionic bonding: electrostatic attractions between oppositely. K+ + i: energy changes for formation of ionic compounds: - formation of k+ requires energy input (ie)--unfavorable. Ie + ea > 0 (requires energy input)
