Lesson 2.2 - Chemical Names and Formulas

You have learned the names of many elements as you studied the periodic table. You also learned that scientists use letter symbols for elements and these letter symbols are used in the periodic table. Scientists and ordinary people communicate about chemicals using chemical names and sometimes chemical formulas. You are going to learn the language of chemical formulas in this lesson.

Read Section 2.3 Chemical Names and Formulas on page 35 in your textbook.

Question 1. What does IUPAC stand for?

Question 2. Is the symbol for hydrogen the same in all languages? What is the symbol for hydrogen?

Question 3. Is the spelling of hydrogen the same in all languages?

Question 4. Students often write S as the symbol for sodium. What is the correct symbol for sodium? What is the correct symbol for sulphur?

Question 5. The symbol for lead is not L; it is Pb. What is the reason for this strange symbol?

 

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Now that you know all about element names and symbols, you can learn about chemical compound names and symbols. Compounds are represented in science using the symbols for the elements that make up the compound and numbers to indicate how many atoms of each element are in the compound. Read the section Chemical Formulas on page 36 in your textbook.

Question 6. What do the letters in a chemical formula tell you?

Question 7. What do the subscript numbers in a chemical formula tell you?

Question 8. What do the subscript letters at the end of a chemical formula tell you?

Question 9. In figure 2.13, the chemical formula of water is explained. How can you tell that the subscript 2 means there are 2 hydrogen atoms rather than 2 oxygen atoms in the molecule?

Question 10. There is no subscript number after the O atom in the chemical formula for water, yet we know there is one atom of oxygen. Why do you think that chemical formula for water is written as H2O(l) and not H2O1(l)?

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Some compounds are found in nature as individual molecules. Water is such a compound. You can have just one water molecule that has 2 hydrogen atoms and 1 oxygen atom. Other compounds are not found in nature as molecules. Table salt that you use when you have a meal is an example. You cannot have one molecule of salt. The chemical formula for table salt is NaCl(s). The term scientists use to describe one NaCl(s) is a formula unit. Use the information in table 2.3 on page 36 to answer the next questions.

Question 11. How many atoms of sodium are in a formula unit of sodium bicarbonate?

Question 12. How many atoms of hydrogen are in a formula unit of sodium bicarbonate?

Question 13. How many atoms of carbon are in a formula unit of sodium bicarbonate?

Question 14. How many atoms of oxygen are in a formula unit of sodium bicarbonate?

Question 15. What is the state of matter of sodium bicarbonate?

Question 16. How many atoms of hydrogen are in a molecule of hydrogen peroxide?

Question 17. How many atoms of oxygen are in a molecule of hydrogen peroxide?

Question 18. What is the state of matter of hydrogen peroxide?

Question 19. What is the difference in the chemical formula of water and the chemical formula of hydrogen peroxide?

Question 20. There is a difference of only one atom of oxygen between water and hydrogen peroxide. Do you think these compounds are similar?

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. What does IUPAC stand for?

IUPAC stands for International Union of Pure and Applied Chemistry.

Question 2. Is the symbol for hydrogen the same in all languages? What is the symbol for hydrogen?

Yes, the symbol for hydrogen is the same in all languages. The symbol for hydrogen is H.

Question 3. Is the spelling of hydrogen the same in all languages?

No, the spelling of hydrogen is not the same in all languages. In the examples given in table 2.2, it is different in every language.

Question 4. Students often write S as the symbol for sodium. What is the correct symbol for sodium? What is the correct symbol for sulphur?

The correct symbol for sodium is Na. The correct symbol for sulphur is S.

Question 5. The symbol for lead is not L; it is Pb. What is the reason for this strange symbol?

Lead is a metal that was known to the ancients. The Latin name for lead is plumbum, and so the symbol was derived from the historical name.

 

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Answers to Questions:

What do the letters in a chemical formula tell you?

The letters in a chemical formula tell you which elements are in the compound.

Question 7. What do the subscript numbers in a chemical formula tell you?

The subscript numbers in a chemical formula tell you how many atoms of each element are in the compound. You might want to use the online dictionary to define subscript and superscript if you are not sure what they mean.

Question 8. What do the subscript letters at the end of a chemical formula tell you?

The subscript letters at the end chemical formula tell you the state of matter of the compound. There are three states of matter that are used: (s) means solid, (l) means liquid, and (g) means gas.

Question 9. In figure 2.13, the chemical formula of water is explained. How can you tell that the subscript 2 means there are 2 hydrogen atoms rather than 2 oxygen atoms in the molecule?

The subscript 2 is after the H symbol for hydrogen and in front of the O symbol for oxygen. This means that there are 2 atoms of H, not 2 atoms of O. This is a very important idea that you must understand perfectly.

Question 10. There is no subscript number after the O atom in the chemical formula for water, yet we know there is one atom of oxygen. Why do you think that chemical formula for water is written as H2O(l) and not H2O1(l)?

The number 1 is not written in any chemical formula because it is redundant. The fact that O is written is enough to tell us there is one oxygen atom; we do not need a number 1 to tell us that. You will not see any number 1 in the simple chemical formulas that you will study.

 

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Answers to Questions:

Question 11.How many atoms of sodium are in a formula unit of sodium bicarbonate?

There is one atom of sodium (Na, element #11 in the periodic table) in a formula unit of sodium bicarbonate. The chemical formula of sodium bicarbonate is NaHCO3(s).

Question 12. How many atoms of hydrogen are in a formula unit of sodium bicarbonate?

There is one atom of hydrogen in a formula unit of sodium bicarbonate.

Question 13. How many atoms of carbon are in a formula unit of sodium bicarbonate?

There is one atom of carbon in a formula unit of sodium bicarbonate.

Question 14. How many atoms of oxygen are in a formula unit of sodium bicarbonate?

There are three atoms of oxygen in a formula unit of sodium bicarbonate.

Question 15. What is the state of matter of sodium bicarbonate?

Sodium bicarbonate is a solid in this example.

Question 16. How many atoms of hydrogen are in a molecule of hydrogen peroxide?

There are two atoms of hydrogen in a molecule of hydrogen peroxide.

Question 17. How many atoms of oxygen are in a molecule of hydrogen peroxide?

There are two atoms of oxygen in a molecule of hydrogen peroxide.

Question 18. What is the state of matter of hydrogen peroxide?

Hydrogen peroxide is a liquid.

Question 19. What is the difference in the chemical formula of water and the chemical formula of hydrogen peroxide?

There is one atom of oxygen in a molecule of water, but there are two atoms of oxygen in a molecule of hydrogen peroxide.

Question 20. There is a difference of only one atom of oxygen between water and hydrogen peroxide. Do you think these compounds are similar?

The only real similarity between water and hydrogen peroxide is that they look the same; they are clear liquids. Water is something we drink and is required for us to live. Hydrogen peroxide is a dangerous liquid. It is poisonous to us, it is used to as an antiseptic to kill bacteria, it is even used in rocket propulsion. What a difference one atom of oxygen makes!

 


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