Introduction to Organic Chemistry
Senior 3 · Chemistry
Introduction to Organic Chemistry
Lesson 1 of 3
20 min
Two hundred years ago chemists divided substances into two kinds: inorganic ones such as salt and metals, and organic ones such as sugar, oils and urea, which only living things seemed able to make. In 1828 the German chemist Friedrich Wöhler heated ammonium cyanate, an inorganic salt, and obtained urea, a compound found in urine. A substance "of life" had been made from a non-living one. The old idea fell, but the name stayed: organic chemistry is now the chemistry of carbon compounds, millions of them, made by plants and animals and in factories alike.
Definition
Organic chemistry: the study of the compounds of carbon, other than a few simple ones (carbon monoxide, carbon dioxide, carbonates and hydrogencarbonates, which are studied as inorganic compounds, as in Unit 1).
Hydrocarbon: a compound of carbon and hydrogen only. Example: methane, .
A carbon atom has four outer electrons, so it forms four covalent bonds. Carbon atoms can also bond strongly to each other, in chains of almost any length, branched chains and rings (Figure 1.1); this is called catenation. And carbon can form double and triple bonds. These three features give an almost endless number of possible structures.
Definition
Catenation: the ability of atoms of an element to bond to one another to form chains and rings. Carbon shows it more than any other element. Example: butane, , has a chain of four carbon atoms.
Displayed formula: a drawing that shows every atom and every bond in a molecule, as for methane in Figure 1.1.
Table 1.1: Typical differences (there are exceptions)
| Property | Organic compounds | Inorganic compounds |
|---|---|---|
| elements present | always carbon, usually hydrogen, often oxygen, nitrogen, halogens | almost any elements |
| bonding | mainly covalent | often ionic |
| melting and boiling points | usually low; many are gases or liquids | often high (ionic solids) |
| solubility | most do not dissolve in water but dissolve in organic solvents | many dissolve in water |
| burning | most burn, giving carbon dioxide and water | most do not burn |
| speed of reactions | usually slow | ionic reactions often very fast |
| number of compounds | many millions | far fewer |
Worked example
Problem. Classify each substance as organic or inorganic: (a) ethanol, ; (b) carbon dioxide, ; (c) glucose, ; (d) sodium carbonate, ; (e) methane, .
Solution. Organic: (a) ethanol, (c) glucose and (e) methane, which are carbon compounds built on carbon–hydrogen bonds. Inorganic: (b) carbon dioxide and (d) sodium carbonate, which are among the simple carbon compounds treated as inorganic.
Worked example
Problem. Most organic compounds burn in plenty of air to give carbon dioxide and water. Write balanced equations, with state symbols, for the complete combustion of (a) methane, (b) ethanol. How could you show that the products contain carbon and hydrogen?
Solution. (a)
(b)
Pass the gases through limewater, which turns milky (carbon dioxide, so the compound contained carbon), and collect the condensed liquid: it turns blue cobalt(II) chloride paper pink (water, so the compound contained hydrogen).
Warning
Common mistakes and safety. (1) "Organic" in chemistry means "a carbon compound", not "grown without chemicals" as on food labels. (2) Not every carbon compound is organic: CO, and carbonates are inorganic. (3) Many organic liquids, such as ethanol and petrol, are highly flammable and their vapours can catch fire from a distance: keep them away from flames. Burning fuels in a closed room can produce poisonous carbon monoxide, so cook and heat only with good ventilation.
Tip
Carbon's "4-C-D" toolkit: 4 bonds, Catenation (chains, branches, rings), and Double or triple bonds.
Practice
Sources and credits
