Chapter 15 - Lecture 7 – Homologous series of Alkenes

ACKNOWLEDGEMENT:

Figure	Source of Figure
Figure 8a	http://www.easychem.com.au/
Figure 8b	http://www.easychem.com.au/
Figure Table 4a	http://www.easychem.com.au/
Figure Table 4b	http://alevelchem.com/
Figure Table 4c	http://www.sciencequiz.net/
Figure Table 4d	http://spmchemistry.onlinetuition.com/

Alkenes:

Alkenes are unsaturated hydrocarbons. They form a homologous series of covalent bonded molecules with the general formula C_nH_2n. That is, each successive member of the series differ by CH₂.’

By unsaturated; it means that 2 adjacent carbon atoms in the chain share a double bond between them.

Example:

Figure 8: Ethene

a) 

Or a more 3D reperesentation b)  

The second bond of the double bond has been formed due to the insufficient amount of hydrogen. In presence of hydrogen, and proper conditions; this bond can easily break to yield a saturated hydrocarbon.

Example:

  

Table 4 shows the physical structures of ethene, propene and butane and iso-butene.

Table 4:

Alkene	Formula	Physical Structure	Isomer(s)
Ethene	C2H4
Propene	C3H6
Butene	C4H8

It is important to note that the double bond may be present anywhere in the carbon chain. 

Referring to Table 4, it is easy to deduce the following conclusions:

1. Melting and boiling point, increases with increase in molecular size.
2. Density increases with increase in molecular size.
3. Viscosity increases with increase in molecular size.

                                                                                       ©Tanzeela Zafar Siddiqui