Key points for OCR AS chemistry Unit 2 (ideal for flash cards, podcasts or just general reviewing) (1)

These are handy key points to help during those last minutes of revision, can also be cut into flashcards or turned into podcasts. These are from the OCR AS chemistry exam cafe cd, containing information from the text book, provided by the authors Dave gent and Rob Richie

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  • Created by: Ike Okoye
  • Created on: 04-06-10 12:31
Preview of Key points for OCR AS chemistry Unit 2 (ideal for flash cards, podcasts or just general reviewing) (1)

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Key points for OCR AS chemistry Unit 2 (ideal for flash cards, podcasts or just general
reviewing) (1)
1. Representing organic compounds
· The empirical formula is the simplest whole-number ratio of atoms of each element present in a
· The molecular formula is the actual number of atoms of each element in a molecule.
· The general formula is an algebraic formula for a member of a homologous series, for example,
CnH2n+2 for an alkane.
· Structural, displayed and skeletal formulae are all used to show organic molecules in different
2. Isomerism
· Structural isomers are compounds with the same molecular formula, but different structural
· Stereoisomers are compounds with the same structural formula, but with a different arrangement
in space.
· E/Z isomerism is an example of stereoisomerism in which lack of free rotation about the C=C bond
allows two different forms to exist.
· Cis-trans isomerism occurs when two hydrogen atoms, on different carbon atoms, adopt either the
same or opposite sides of the C=C.
3. Hydrocarbons from crude oil
· A hydrocarbon is a compound containing hydrogen and carbon atoms only.
· Crude oil is separated by fractional distillation, in which the fractions have different boiling points.
· The carbon atom in hydrocarbons, as in alkanes, is forming four single covalent bonds in a
tetrahedral arrangement.
· As the chain length of the hydrocarbons increases, so too does the size of the van der Waals' force,
resulting in a high boiling point.
4. Reaction of alkanes
· Alkanes are hydrocarbons, and their molecules are weakly attracted by van der Waals' forces.
· Alkanes are saturated hydrocarbons; this means that they consist of only carbon single bonds.
· Alkanes are mainly used as fuels, when combusted they provide heat energy.
· Alkanes react with halogens in ultraviolet light to form halogenoalkanes. This is a free radical
substitution mechanism.

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· Alkenes are unsaturated hydrocarbons; they consist of one or more carbon double bonds, making
them more reactive than alkanes.
· A double bond consists of a sigma and a pi bond. The pi bond is formed by the adjacent overlap of
· The pi bond is the reactive part of the double bond; the pi bond is of lower reactivity.
· The arrangement of the bond about the carbon double bond is trigonal planar, with an internal
angle of 120°.
6.…read more

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