Dive into the World of Chemistry with Our Pearson Edexcel GCSE Organic Chemistry Notes! Uncover the fascinating realm where carbon compounds take center stage, exploring the foundational principles of organic chemistry. Our meticulously crafted notes cover key topics, from hydrocarbons and function...
4.2 understand how to represent organic molecules using empirical formulae, molecular formulae,
general formulae, structural formulae and displayed formulae.
Molecular formula: shows actual number of atoms in a molecule
Empirical formula: shows the simplest ratio of atoms in a compound
General formula: shows relationship of homologous series, is an equation to calculate the number of
atoms. (e.g. alkanes is CnH2n+2, alkenes is CnH2n)
Structural formula: shows how atoms in a molecule are joined together
Displayed formula: full structural formula, shows all bonds in a molecule as individual lines
These are different formulas for Butane:
Displayed formula:
Structural formula: CH₃ – CH₂ – CH₂ – CH₃
Molecular formula: C₄H₁₀
Empirical formula: C₂H₅
General formula: Because it is an alkane, the general formula is CnH2n+2.
4.3 know what is meant by the terms homologous series, functional group and isomerism
Functional Group: an atom/a group of atoms that determines the chemical properties of a
compound.
e.g. functional group of alcohols is -OH, alkenes is C=C (double bond)
Homologous Series:
- same general formula
- similar chemical properties because they have the same functional group.
- a trend in physical properties
Isomers: molecules with the same molecular formula but with a different displayed formula.
,Rules in naming alkanes and alkenes
Rule 1) Find the longest chain of carbons. (It does NOT have to be straight.) This goes at the end of
the name (meth, eth, prop)
Rule 2) Identify any side branches (methyl, ethyl, propyl groups). These go just before the longest
chain name.
Rule 3) If a side chain occurs more than once, indicate how many times it occurs. This goes just
before the branch name. di - two, tri = three, tetra = four. After that, the prefixes are the same as for
chain-length.
Rule 4) When necessary, indicate which carbon the side-branch comes from by counting from the
end of the main chain that gives the lowest possible number.
4.4 understand how to name compounds relevant to this specification using the rules of
International Union of Pure and Applied Chemistry (IUPAC) nomenclature
Name Number of Carbons in Longest
Chain
Meth 1
Eth 2
Prop 3
But 4
Pent 5
Hex 6
Hep 7
Naming Straight Chain Alkanes:
Alkanes: Simplest hydrocarbon.
e.g. displayed formula for ethane (C₂H₆) is:
- This is called ethane because "eth" means there are 2 carbons in its longest chain, and "ane" means
that it is an alkane with single bonds.
, Another example is pentane's displayed formula (C₅H₁₂):
- This is called pentane because "pent" means there are 5
carbons in its longest chain, and "ane" means it is an alkane with single bonds.
Pentanes can be drawn differently:
- This is still called a pentane as it has 5 carbons in its longest chain, joined together by single bonds.
They can also be drawn in weird structures with different angled bonds, like this:
However, it is still a pentane as it has 5 carbons with single bonds – has an
ethyl group attached.
Naming straight chain ALKENES:
Alkenes: C=C double bond
e.g. the displayed formula for ethene (C₂H₄) is:
Propene (C₃H₆):
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