Alkenes

• The general formula of an alkene is

  CnH2n
• molecules with C=C double bonds are unsaturated as they can form more bonds with extra atoms in addition reactions
• alkenes are quite reactive as the two pairs of electrons in the C=C bond have a high electron density
• in electrophilic addition, the double bond in an alkene is attacked by an electrophile
• electrophiles are positively charged ions
• Testing for unsaturation

  When you shake an alkene with orange bromine water the solution turns from orange to colourless
• alkenes undergo electrophilic addition with hydrogen halides to form halogenoalkanes
• More stable carbocations are more likely to form than less stable ones
• Polymers are formed from monomers
• the double bonds in alkenes can form polymers by addition polymerisation
• alkene monomers are unsaturated but once they form polymers become saturated
• the main carbon chain in a poly alkene is normally non polar
• addition polymers are very unreactive and polyalkenes are chemically inert
• the monomers within a polymer chain have strong covalent bonds
• the intermolecular forces between polymer chains are very weak
• longer polymer chains with fewer branches have stronger intermolecular forces - making these polymers stronger and more rigid
• Poly(chloroethene) is also known as PVC is an addition polymer
• in PVC the covalent bonds been the chlorine and carbon atoms are polarised creating permanent dipole-dipole forces between the polymer chains making it a hard but brittle material

  
• plasticicers make polymers more flexible as the molecules push apart the polymer chains which reduces the intermolecular forces