Organic compounds have a significant role in our life because they are widely used in everywhere.
Thousands of organic compounds are discovered so far by scientists in the world. With discovering lot of compounds, organic chemistry was born. In this chapter we are going to discuss how melting and boiling points of organic compounds vary.
Ethanol and n-propanol belongs to alcohol group. Boiling points of ethanol and n-propanol are 78.240C and 970C respectively. Boiling point of ethanol is smaller than n-propanol. You, will see more examples of these type of compounds later in this tutorial.
Written by: Heshan Nipuna, updated: 2020/02/25
Following facts are important when we compare melting and boiling point values of organic compounds. Later, in this tutorial, we are going to look, how these factors are affected for boiling points of organic compounds.
Alkanes, alkenes and alkynes are hydrocarbons and we are going to see the trend of melting and boiling points of them.
Alkanes are non polar molecules. Therefore, there are only Van der Waals forces between alkane molecules. Van der Waals forces are the weakest intermolecular forces type. When relative molecular mass increases in alkane compounds, melting and boiling points values are also increased.
Melting and boiling points increases alkane, alkene, alkyne respectively.
Ethane is an alkane which is a non-polar compound. Ethyne (alkyne compound) has the highest melting and boiling point.
See this example. Compare boiling points of ethanol and ethyl chloride compounds. Both organic compounds have two carbon atoms. Ethanol's boiling point is 78.370C. Ethyl chloride's boiling point is 12.30C. We know ethanol can make strong hydrogen bonds. But, there are only di-pole di-pole attractions between ethyl chloride molecules. Di-pole di-pole attractions are weaker than hydrogen bonds. Due to ability of making hydrogen bonds, boiling point of ethanol is high.
Benzene, an aromatic organic compound which has the boiling point of 80.10C. Benzene forms weak Van der Waals forces. But benzene has a higher molecular mass compared with simple alkanes such as methane, ethane..
Due to higher molecular mass, boiling points of benzene is higher than simple alkanes.
Halogen atom is more electro negative than carbon atom. So C-X bond is polarized. There are dipole dipole interaction between alkyl halide compounds. These interactions are much stronger than intermolecular forces between alkanes,
Now we discuss some problems by comparing different elements and compounds which have different melting and boiling points. These problems very important in examinations. Study them carefully.
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