Science for WA 10 02 The chemical world

Page 40ISBN 9780170181518

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The major classes of chemical substances Figure 2.4 is a chart that shows the major classes of chemicals known today. Within each class, there are many, many families. Only some examples are shown.

02 Nelson Science for WA Yr 10 TXT 5pp.indd 40 13/01/10 12:17 PM

 

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A typical fat molecule

BLM 2.1 The molecules quiz

Science for WA 10 02 The chemical world

Page 38ISBN 9780170181518

Organic and inorganic compounds Before the 1800s, chemists were aware of some of the elements, although it was not always clear whether a newly discovered substance was an element or a compound. The noble gases were not yet known. At that time, compounds were classified as either organic compounds or non-organic compounds, which were described as inorganic compounds.

The term organic came about because it was once believed that only living organisms could make these compounds. In fact, it was suggested that organic compounds had different properties from inorganic compounds because they contained the ‘vital force of life’.

However, the humble urea molecule present in our urine proved this was not the case. In 1828, the German chemist Friedrich Wöhler accidentally synthesised (built up, or manufactured) urea in his laboratory, when trying to make an ionic compound called ammonium cyanate. Urea has the chemical formula (NH2)2CO. Since that discovery, thousands of organic substances have been synthesised, including pharmaceuticals and plastics.

Today, chemical compounds are still classified as organic or inorganic. Of course, by ‘organic’, chemists do not mean ‘free of pesticides and herbicides’! Organic compounds are defined as compounds of carbon. Hydrogen is always present in these compounds as well. Other elements may also be present (Figure 2.2).

Some compounds of carbon and hydrogen, however, are classified as inorganic. An example of this is sodium hydrogen carbonate (commonly known as bicarbonate of soda), NaHCO3.

Amazingly, there are literally millions of organic compounds. There are at least 10 times as many organic compounds as inorganic compounds, and more are being discovered every day. The study of inorganic chemicals and organic chemicals, known as inorganic chemistry and organic chemistry, are considered two of the major fundamental branches of chemistry today. The other major branch is known as physical chemistry.

Figure 2.2 Models of some organic and inorganic molecules

>>Alchemists once thought that the golden colour of urine meant it might contain gold, or the mythical substance that would turn base metals into gold – the philosopher’s stone. Many therefore spent a great deal of time experimenting with urine. Of course they did not succeed, because urine does not contain gold or any substance that will turn other metals into gold. However, their research led to some interesting discoveries.

White phosphorus was discovered by the German alchemist Hennig Brandt in 1669 when he heated fermented urine to a very high temperature. Much to his great surprise, he produced a waxy white substance that glowed in the dark! This new element was named from the Greek word phosphoros, meaning ‘bringer of light’.

Just over 100 years later, in 1773, the French chemist Hilaire Rouelle boiled some urine dry. He noticed that white crystals were produced. This was the first time that urea was isolated.

02 Nelson Science for WA Yr 10 TXT 5pp.indd 38 13/01/10 12:17 PM

 

BLM 2.2 More simple molecules

Page 39ISBN 9780170181518

Exercise 01Answer the following questions in your journal.Questions 1–4 are all multiple-choice questions. Select the one correct or best answer.1 Which one of the following statements about organic compounds is true?

A Organic compounds can only be produced by living organisms.

B All organic compounds contain carbon and hydrogen.

C All compounds containing carbon and hydrogen are classifi ed as organic compounds.

D Organic compounds are compounds that occur in nature.

2 About how many organic compounds are known to exist?

A Hundreds

B Thousands

C Tens of thousands

D Millions

3 Which one of the following compounds would be classifi ed as organic?

A Propane, produced when plants and animals decompose in the absence of oxygen, C3H8

B Carbon monoxide, produced when coal and wood burn in a limited oxygen supply, CO

C Water, produced during the breakdown of proteins and fats and oils in the body, H2O

D Calcium hydrogen carbonate, produced when water trickles through limestone, Ca(HCO3)24 What is the fi rst organic compound that was synthesised in a laboratory?

A Carbon dioxide

B Alcohol

C Urea

D Nylon

Figure 2.3 An organic chemist at work

>>Strangely, although they certainly are banned from being sprayed onto organic foods, almost all pesticides and herbicides are in fact organic compounds. On the other hand, living organisms can make inorganic compounds. For example, oysters manufacture pearls and shells, both of which are made from the inorganic compound calcium carbonate.

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