Atoms, Bonds & Groups


Structural isomers- molecules with the same molecular formula but a different structural arrangement.

The different structures = different chemical properties.

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Structual Isomers- molecules with the same molecular formula but a different structural arrangement. Different structures = different properties. 

Stereoisomers- compounds with the same structural formula but different arrangement of atoms. 

E (cis)/ Z (trans)- when there is a non hydrogen group and hydrogen on each C of a C=C bond. 

E- transisomer = atoms on different side

Z- cisisomer = atoms on the same side

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Organic Reagents

Organic Reagents

Homolytic Fission: each atom has an unpaired electon (radical)

Heterolytic Fission: one of the bonded atom takes both pair of electrons (cation+ve or anion-ve) 

Nucleophile is an atom that is attracted to an electron deficient, they donate an electron pair, for example, :Br

Electrophile is an atom that attacks an area of high electron density, accepting an electron pair, for example, HBr

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Organic Reagents: Reactions

Addition Reaction: 2 reactants --- 1 product

Substitution Reaction: 2 reactants --- 2 products

Elimination Reaction: 1 reactant --- 2 products

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- carbon dioxide = carbon molecules

- 1/2 water= hydrogen atoms

Incomplete combustion

- Caused when there is a lack of oxygen, carbon monoxide and water are formed

Carbon monoxide is colourless and odourless. 

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Substitution of Alkanes

Radical substitution 

 - a covalent bond is BROKEN to form radicals. A Hydrogen is subsituted for a halogen atom. 

1) Initiation is when the free radicals are generated by ultraviolet radiation: the radicals produced are very reactive. 

2) Propogation is when the two repeated steps that build up the products. 

Methane reacts with the chlorine radical and a C-H bond is broken forming methyl radical.      Methyl radical reacts with chlorine, forming chloromethane. 

This reaction carries on until there are no more reactants. = CHAIN REACTION.

3) Termination is the step at the end when two radicals form a molecule by combining. ALL radicals are removed to stop the reaction. 

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One double bond has general formula of Cn+H2n    Alkenes more reactive than alkanes. 


The Pi bond fixes the carbon positions, preventing rotation. 

- There are 3 regions of electron density around each carbon. Pair of electrons repel each other. Trigonal Planar Shape = 120 Degrees. 

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Curly Arrows

Curly Arrows

Show the movement of an electron pair in the breaking/formation of a covalent bond. 

- electron pair in the Pi bond is attracted to the hydrogen, bond breaks.

- New bond forms: C-H.

- H-Br bond breaks, electron pair goes to the Bromine.

- The carbocation formed is unstable and reacts with bromide ion. 

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Industrial use of alkenes

Industrial use of alkenes

Plastics are one of the industrial products produced from ethene. 

Polymer: A long molecular chain built up from monomers. 

Monomer: Small molecules that are combined to form polymers.

Addition Polymerisation is the process by which unsaturated alkene molecules (monomers) add on to a growing polymer chain, one at a time, to form a long saturated molecular chain (the addition polymer).

Radical Polymerisation: Temperature of 200 Degrees and High pressure. This leads to branching and production of polymer mixtures. 

The Ziegler-Natta Process: Specialist catalyst (Titanium Chloride) and 60 Degrees. When the alkene is passed over the catalyst with a low conversion and the unreacted alkenes is passed over the catalyst repeatedly. Causes non brances poly(ethene). 

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