4.1 Flashcards
Homologous series
Families of organic chemicals.
Must have same functional group and successive members differ by only a CH2 unit.
Aliphatic hydrocarbons
In which the carbon atoms are joined together in either straight (unbranched) chains or branched chains.
Alicyclic hydrocarbons
In which the carbons are joined together in a ring structure but are not aromatic.
Aromatic hydrocarbons
In which there is at least one benzene ring in the structure.
General formula
Simplest algebraic formula for all the organic compounds in a homologous series and can be used o generate a molecular formula. E.g. CnH2n+2
Displayed formula
Shows the relative positions of all atoms in a molecules and the bonds between them. Remembers to show bonds between OH groups etc.
Structural formula
Gives the minimum detail for the arrangements of atoms in a molecule. E.g. butane CH3(CH2)2CH3
Empirical formula
Shows the simplest whole number ratio of atoms of elements in a compound.
Molecular formula
Shows numbers and types of atoms in a compound.
Bonding in alkanes
Each covalent bond has a direct overlap of the electron clouds from each atom making a sigma bond.
So C-C and C-H are examples of sigma bonds.
In the alkane structure every carbon atom has a tetrahedral shape with a bond angle 109.5 degrees.
Branching alkane boiling points
More branched, fewer surface area interactions there are between molecules, as they cannot fit together neatly.
Branched have fewer dipole-dipole interactions compared to straight chain isomer with the same molecular formula. Branched = lower boiling point
Reactivity of alkanes
Low reactivity with most reagents, because:
All the covalent bonds have high bond enthalpies, a large amount is required to break the bond.
C-H sigma bonds have very low polarities, as the electronegativity’s are almost the same.
Products of incomplete combustion
Carbon soot, water, carbon dioxide and carbon monoxide.
Bonding in alkenes
C-H bonds are sigma bonds.
C=C
A sigma bond is formed between two carbon atoms using the direct overlap of the electron clouds of two atoms.
The pi bond is formed by the electrons in the adjacent P-orbitals overlapping above and below the carbon atoms. This can only be formed after a sigma bond has formed.
How does the pi bond hold the alkene bond in place?
Restricts movement around the pi bond. So alkene molecules have a flat shape in the region of the double bond.
