Topic: Intro to Redox: Assigning Oxidation Number
Do Now:What is oxidation number for the following Metals in the ionic compounds below1. Fe2O3
2. FeO3. AgCl4. K2S5. Mn2O7
Redox Reactions = oxidation-reduction reaction
• Electrons transferred from 1 atom to another
• Redox reactions: – All single-replacement rxns– All combustion rxns
• Double Replace is never Redox
OIL RIG - memorize O – Oxidation I - isL - loss of electron
R - ReductionI - isG – gain of electron
REDOXOxidation & Reduction reactions are complementary reactions• Something is oxidized - __________ electrons• While something is reduced - ________ electrons• They occur every day – Respiration– Photosynthesis– combustion
losesgains
To understand these Redox Rxns we must first understand Oxidation
numbers
Rules to Assigning Oxidation Numbers( oxidation # =what an atoms charge would be if it owned all it’s electron
exclusively (not sharing)
#1: individual atom (monatomic, diatomic, polyatomic , but only 1
type of atom) = 0
#2for an ion
oxidation number = charge
Ca+2 = +2 Cl-1 = -1 Al+3 = +3
# 3• When Fluorine is in a compound F is
always ____________
CF4 C= ___ F = _-1_
OF2 O= ___ F = _-1_
-1
+4
+2
# 4
• When in a Oxygen is in a compound, O is AMLOST always ________– EXCEPT when with Fluorine• OF2 O= ____ F = _-1_
– Except when O2 is bonded with group 1 or 2 metal• Then it’s a ____________________–K2O2 = K = ____O = ____
-2
Peroxide
+2
+1 -1
Don’t forget O2 by itself has an
oxidation number of 0
#5
H is nearly always +1 • except if bonded to metal then -1• H2O H = ____O = ____
• H2SO4 H = ____SO4 = ____• LiH Li = ____H = ____• CaH2 Ca = ____H = ____
• NH3 N = ____H = ____
+1 -2+1 -2+1 -1+2 -1
+1-3
#6
• For neutral compounds, sum of oxidation numbers = 0
• H2O 2H = +1 = +2 1O= -2 = -2 +2-2 =0
• H2SO4 2H = +1 = +2 1SO4= -2 = -2 +2-2 =0• LiH 1Li = +1 = +1 1H= -1 = -1
+1-1 =0• CaH2 1Ca = +2 = +2 2H= -1 = -2 +2-2 =0
#7• For polyatomic ions, sum of oxidation numbers = charge of
ion
• SO4-2 1S = ___= ___ 4O= ___ = ____
___ + ___ =-2
• NO3-1 1N = ___= ___ 3O= ___ = ____
___ + ___ =-1
-2
-2
-8
-8+6
+6+6+6 -2
-6
-6+5
+5+5+5 -2
# 8
• If covalent compound – both elements are nonmetal, like to gain electrons (both negative?! – NO)–Assign negative to the more
electronegative element–SiCl4: Si = +4, Cl = -1
Assign Oxidation #’s• KCl
• CaBr2
• CO
• CO2
• Al(NO3)3
• Na3PO4
• H2S
• NH4+1
• SO3-2
K = +1, Cl = -1
Ca = +2, Br = -1
C = +2, O = -2
C = +4, O = -2
Al = +3, O = -2, N = +5
Na = +1, O = -2, P = +5
H = +1, S = -2
N = -3, H = +1
S = +4, O = -2