19/5/15
Redox continued
Oxidation
* Loss of electrons
* More positive oxidation numbers
* Reducing agents
Reduction
* Gain of electrons
* More negative oxidation number
* Oxidizing agents
In summary - all components of a molecule must have oxidation charges which sum to equal 0 if the charge is not given.
Hydrogen can act as an oxidant and reductant
Reductants are often metals
* Mostly have ½ valence electrons
* All have low electronegativity
* Achieve stable out arrangement by donating outer valence electrons to an oxidant. In case of metals, will be oxidised to its ion
* The metal ion is the conjugate oxidant to the metal
Oxidants are often non-metals
* Non metals with high electronegativity need electrons to complete their valence shell
* Will accept electrons from sufficiently strong reductants
* Form negatively charged ions
How to identify redox reactions
+2 -2
Zc + HCl → ZnCl + H
0 0 0
Changes were made to Zn and H
Species
Before Reaction
After Reaction
Oxidation State Change
Zn (solid)
0
+2 (in ZnCl₂)
Oxidized (lost 2e⁻)
H (in HCl)
+1
0 (in H₂ gas)
Reduced (gained e⁻)
If the oxidation numbers of all components do not change, the reaction is not redox
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Redox half reactions:
Explaining the two complementary processes which take place in a redox reaction.
Mg + Br → MgBr2
0 0 +2 -1 (2 Br, charge = -2)
Mg → Mg 2+ + 2e (neutralises)
Br2 + 2e → 2Br-
In short, Bromine gains electrons from Mg, that Mg loses to have a full outer shell.
This assumes that the reaction takes place in acidic conditions, where protons are present.
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Write the two half equations for the following reaction:
Cl2 + 2e→ 2Cl- (reductive reaction, gained electrons and RIG)
2I- → I2 + 2e (oxidation reaction loses electrons and creates excess, OIL)
Cl + 2I- → 2Cl- + I2
IS a redox reaction
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Br2 + 2e → 2Br-
SO32- + H2O → SO42- +2H+
Use water to check - what happens?
Br2 + SO32- H2O → 2Br- + SO42- + 2H+
IS a redox reaction
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Balancing half reactions
MnO4- + Fe2+ → Mn2+ + Fe3+
Unbalanced half reactions:
MnO4- → Mn2+
Fe2+ → Fe3+
Which is oxidation/reduction?
+7 +2
MnO4- + 8H+ → Mn2+ + 4H2O (just added H+ because O4 was present)
MnO4- + 8H+ + 5e → Mn2+ + 4H2O
At this stage, count all hydrogens and ensure the charge is balanced.
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Balancing redox reactions under basic conditions
Balance the half equations as previously (though it’s in acidic conditions)
* Add OH- to neutralise H+ on either side of the equation
* Form water by combining these
* Combine the half reactions and check that the elements and charges are balanced
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Corrosion is a redox reaction
* Most metals are found in their oxidised form as oxides
* Corrosion of iron is called rusting
* Corrosion is the metals going back to their original form (oxidised)
End of lecture
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20/5/25
Organic chemistry
* Carbon compounds
* Natural products
* Bonding and structure of carbon
* Name and draw simple organic compounds
* Identify functional groups
Organic chemistry is the study of molecules containing carbon
Organic chemistry started as the chemistry of life, which was thought of to be different from chemistry in the lab.
Organic molecules can be synthesised
* can be created artificially but understanding aspects of reactivity
* Contain carbon
* Organic compounds are prepared by chemical synthesis
* Naturally occurring compounds have been prepared in the lab by synthetic organic chemists.
Bonding in carbon based molecules
Carbon has four valence electrons - it can form bonds with 4 other atoms
* These bonds are covalent and shared between atoms
* Nitrogen could form 4 bonds, oxygen 2, and fluorine 1, ect.
* This enables more structural diversity than molecules composed of other atoms
Why is carbon special?
* Stability - it bonds strongly to other carbon
* Oxidation of carbon is slow - needs high temperature to start
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VSEPR
Drawing methane (CH4) to represent trigonal pyramidal shape
Check notebook for physical drawings
Molecules are named based off of the number of carbons they have
If a molecule is saturated is has all the hydrogens that can bond with the carbon
Eg: butane
* 4 carbons, so 10 hydrogens
Octane - 8 carbons 18 hydrogens.
Paraffin wax - C25H52. H = 2C + 2
Ethane formulas
* CH3CH3
* C2H6 - doesn't imply structure
* —
Line - shows carbon bond. Implication is that a hydrogen atom is as the end of every carbon bond
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Carbon can have double bonds
* this results in 120 degree bonding angle, as they cannot bend
There can be more than one carbon-carbon double bond
These molecules are called dienes and trienes
^^butadiene and butatriene
Carbon can have triple bonds
* This results in 180 degree bonding angles
(CH3)2CHCHCHCOCH3 drawing in notebook - hydrogen atoms don’t have to be drawn.
Drawing rules:
* Draw double bonds as far from other atoms as possible
* It doesn't matter which direction you start
* Don't forget that atoms in a straight chain are in a zig zag
Carbon compounds can exist as isomers
* These are structures with the same formula but different ways of being put together
* How many molecules are there with five carbons and only single bonds?
Eg - linear arrangement or other formations?
C6H14 structures
End of lecture
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Study notes:
Alkanes are saturated and have no double bonds
Alkenes by definition contain one or more carbon double bond
Alkenes with one double bond have the formula H = 2C
When labeling the location of a double bond, a number will be added to the formula.
Carbon Atoms
Prefix
1
meth-
2
eth-
3
prop-
4
but-
5
pent-
6
hex-
7
hept-
8
oct-
9
non-
10
dec-
Bond Type
Suffix
Example (C4)
Notes
Single bonds
-ane
butane
Saturated (alkane)
Double bond
-ene
but-1-ene
Unsaturated, use lowest possible locator
Triple bond
-yne
but-1-yne
Unsaturated, locator shows ≡ position
Formula
Type
Name
Why? (Locator Explanation)
CH₂=CH–CH₃
Alkene
prop-1-ene
Double bond starts at carbon 1
CH≡C–CH₂–CH₃
Alkyne
but-1-yne
Triple bond starts at carbon 1
CH₃–CH=CH–CH₃
Alkene
but-2-ene
Double bond starts at carbon 2
CH₃–C≡C–CH₂–CH₃
Alkyne
pent-2-yne
Triple bond starts at carbon 2
Remember - final ane/ene/yne is based upon positioning in the alphabet. a, then e, then y.
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22/5/25
Organic chem part II
Alkane
* Single bonds
* Tetrahedral
* 109.5o
Alkene
* Double bonds
* Trigonal planar
* 120o
Alkyne
* Triple bonds
* Linear
* 180o
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Naming alkanes
Methane indicates a single carbon
Ethane indicates a double carbon
Propane indicates a triple carbon
The longest carbon chain is used to determine the type of molecule that we have.
Many compounds have more than one chain
* These are called substituents.
* The number is the longest chain, and its used as the principal name if the compound
Substituents are referred to as Alkyl groups. These are atoms or groups of atoms which replace hydrogen and get attached to the carbon in the longest carbon chain.
When alkanes are connected to substituent groups, they will end with the “yl” suffix. Eg Methyl, Ethyl, Propyl, Butyl.
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Isopropyl - it's called iso because all of the carbons except for one form a continuous chain.
Neopentyl - all but two carbons form a continuous chain.
Steps for naming alkanes:
* 1: find the longest carbon chain
* 2: number the carbon chain so you have the most substituents and lowest number at each substituent
* 3: identify the type of substituent
If there are many substituents then indicate this with di / tri ect. Put this before the chain name (pent/hex etc).
When naming the positioning of substituents, find the lowest numbers and use those.
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Functional groups
Use ene / yne suffixes for substituents that have a double / triple bond
Include a humber alongside the suffix to show where the double bond is
# of Carbons? (1 - Meth, 2 - Eth, 3 - Prop...)
Largest # of Carbon Bonds? (1 - ane, 2 - ene, 3 - yne, etc.)
Functional Groups? (Alcohol - OH, Aldehyde - CHO, etc.)
Position of Functional Group? (If applicable, like 2- or 3-)
Substituents? (Methyl, Ethyl, etc.)
Suffix/Ending? (Alkane, Alkene, Alkyne, etc.)
1 Carbon: Meth (CH₄)
Single bond: -ane (Methane)
Alcohol: -OH (Methanol)
If alcohol: Position 1 in case of chain (Methanol)
Methyl: If branch off chain
Alkane: Methane, Alcohol: Methanol
2 Carbons: Eth (C₂H₆)
Single bond: -ane (Ethane)
Aldehyde: -CHO (Ethanal)
Position 1 in aldehyde (Ethanal)
Ethyl: If branch (Ethyl group)
Alkane: Ethane, Aldehyde: Ethanal
3 Carbons: Prop (C₃H₈)
Single bond: -ane (Propane)
Ketone: -CO (Propanone)
If ketone: Position 2 in case of chain (Propanone)
Propyl: If branch (Propyl group)
Alkane: Propane, Ketone: Propanone
4 Carbons: But (C₄H₁₀)
Single bond: -ane (Butane), Double bond: -ene (Butene)
Carboxylic Acid: -COOH (Butanoic acid)
If acid: Position 1 in carboxylic acid (Butanoic acid)
Butyl: If branch (Butyl group)
Alkane: Butane, Acid: Butanoic Acid
5 Carbons: Pent (C₅H₁₂)
Single bond: -ane (Pentane), Double bond: -ene (Pentene)
Ester: -COO- (Ethyl acetate)
If ester: Position 2 in chain (Ethyl acetate)
Pentyl: If branch (Pentyl group)
Alkane: Pentane, Ester: Ethyl acetate
6 Carbons: Hex (C₆H₁₄)
Single bond: -ane (Hexane), Double bond: -ene (Hexene)
Alcohol: -OH (Hexanol), Ether: -O- (Ethoxy)
Alcohol: Position 1 in chain (Hexanol)
Hexyl: If branch (Hexyl group)
Alkane: Hexane, Alcohol: Hexanol
7 Carbons: Hept (C₇H₁₆)
Single bond: -ane (Heptane), Double bond: -ene (Heptene)
Amino: -NH₂ (Heptanamine)
If amine: Position 1 in chain (Heptanamine)
Heptyl: If branch (Heptyl group)
Alkane: Heptane, Amine: Heptanamine
8 Carbons: Oct (C₈H₁₈)
Single bond: -ane (Octane), Double bond: -ene (Octene)
Aldehyde: -CHO (Octanal)
If aldehyde: Position 1 (Octanal)
Octyl: If branch (Octyl group)
Alkane: Octane, Aldehyde: Octanal
9 Carbons: Non (C₉H₂₀)
Single bond: -ane (Nonane), Double bond: -ene (Nonene)
Ketone: -CO (Nonanone)
If ketone: Position 2 in chain (Nonanone)
Nonyl: If branch (Nonyl group)
Alkane: Nonane, Ketone: Nonanone
Halogens as functional groups are treated as substituents on alkane chain.
Br - bromo
F - fluoro
Cl - Chloro
I - iodo
End of lecture
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