Lesson 1.1 - Pure Substances

You learned the difference between pure substances and mixtures in Section 1. You learned that pure substances contain only one kind of particle. It didn't take people very long to figure out that some pure substances could be broken down into other pure substances if they used some very strong chemical reactions. For example pure copper and iron could be made by taking the ores of the metals and reacting them with carbon. And so the classification of substances continued to improve as time marched on.

Most ancient Greek philosophers believed that all matter on Earth was composed of only four fundamental substances: earth, air, fire, and water. They believed that if you combined these four fundamental substances in exact proportions of some kind you could make any substance on earth. That led to many experiments where early scientists would try recipes such as 10% earth, 25% air, 40% water, and 25% fire and see if that made gold. You can easily guess that none of these experiments produced any gold. Some philosophers, such as Democritus whose picture is shown here, had their own ideas about matter that were much closer to the truth. The experiments that were performed to try to make gold and other precious metals did lead to new discoveries about elements. By the middle of the 19th century scientists had discovered about 64 elements. Today we know of 112 elements.

To begin your study of the pure substances, elements and compounds, read page 22 in your textbook.

Question 1. What is alchemy?

Question 2. What is an alchemist?

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As more and more elements were discovered, scientists began trying to organize them. The first person to succeed in a big way was Dmitri Mendeleev. Read page 24 in your textbook to learn how Mendeleev arranged the elements into a table.

Question 3. What was the first thing that Mendeleev did so that he could start to organize the known elements?

Question 4. What was the important idea behind putting the cards into groups (columns)?

Question 5. How did he then organize the elements within a group?

Question 6. How did he then organize the groups?

Question 7. There seemed to be elements missing in his table. What did Mendeleev do with these holes in his table?

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There is more than one periodic table of elements since many people made their own periodic tables. To see a copy of Mendeleev's original periodic table and some other pretty neat periodic tables try visiting the following sites (there is no guarantee that the sites are available at all times). Be sure to try clicking on some of the elements to see what kind of information is available; some even have sound to let you hear the correct pronunciation. Don't tell anyone you visited the last site in the list, they may think that you are having fun in this science course.

http://www.superliminal.com/pfractal.htm
http://www.webelements.com/
http://www.uky.edu/Projects/Chemcomics/

A simple version of the modern periodic table is located on the back cover of your textbook. To learn how to find information using a periodic table, read page 25 in your textbook. Then answer the following questions using the complete periodic table on the inside of the back cover of the textbook.

Question 8. How many periods are there in the modern periodic table?

Question 9. How many groups are there in the modern periodic table?

Question 10. How many elements are there in the modern periodic table?

Question 11. Each element has 5 kinds of information given in the periodic table. What are the 5 different pieces of information?

Question 12. How many elements are there in period 3?

Question 13. How many elements are there in group 18?

Question 14. What element is found where the 5th period and 17th group intersect?

Question 15. In which period is the element oxygen found?

Question 16. In what group is the element magnesium found?

Question 17. This question is a bit tougher! What period and group is the element gold found?

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Answers to Questions:

Question 1. What is alchemy?

Alchemy is a complicated mixture of religion, science, and philosophy that was practiced until the 18th century.

Question 2. What is an alchemist?

An alchemist is a person who practices alchemy. Brand was an alchemist who discovered the element phosphorus in 1669.



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Answers to Questions:

Question 3. What was the first thing that Mendeleev did so that he could start to organize the known elements?

He wrote all the known information for each element on a separate file card.

Question 4. What was the important idea behind putting the cards into groups (columns)?

He put elements that had similar properties into groups or columns.

Question 5. How did he then organize the elements within a group?

He arranged the elements from lightest to heaviest within each group.

Question 6. How did he then organize the groups?

He arranged the groups so that the lightest groups were on the left and the heaviest were on the right.

Question 7. There seemed to be elements missing in his table. What did Mendeleev do with these holes in his table?

He predicted that these elements had not yet been discovered and most importantly, predicted the properties of the missing elements. This enabled other scientists to look for the missing elements based on his predictions.



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Answers to Questions:

Question 8. How many periods are there in the modern periodic table?

There are 7 periods.

Question 9. How many groups are there in the modern periodic table?

There are 18 groups.

Question 10. How many elements are there in the modern periodic table?

The total number of elements in this periodic table is 112. This number may change if other elements are discovered.

Question 11. Each element has 5 kinds of information given in the periodic table. What are the 5 different pieces of information?

The five pieces of information for each element are:
路 Element name
路 Element number
路 Element symbol
路 Element mass
路 State of matter at room temperature and pressure

Question 12. How many elements are there in period 3?

There are 8 elements in period 3.

Question 13. How many elements are there in group 18?

There are 6 elements in group 18.

Question 14. What element is found where the 5th period and 17th group intersect?

Iodine is the element found at the intersect of period 5 and group 17.

Question 15. In which period is the element oxygen found?

Oxygen (element number 8) is in period 2.

Question 16. In what group is the element magnesium found?

Magnesium (element number 12) is in group 2.

Question 17. This question is a bit tougher! What period and group is the element gold found?

Gold (element number 79) is in period 6 and group 11.


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