Properties of Elements and Compounds - Science Lessons for Grade 4 Students

Properties of Elements and Compounds

Harry was tired of school. The only subject he enjoyed was science. In fact, the only teacher he felt like not killing was the science teacher, Mr. Gerard. He went to school just to sit in his class, and listen to his words which transported him to the amazing world of science. One day, Harry found Gerard looking at something very closely in the science laboratory. He went to the teacher and asked what he was doing.

Harry: Good morning, Mr. Gerard. You are all alone in the science lab today.

Mr. Gerard: Good morning, Harry. Yes, I was just looking at the mess that the Grade 11 students made in this lab.

Harry: What happened?

Mr. Gerard: Well, they were doing an experiment which was supposed to produce hydrogen and oxygen, but they did not manage to do so apparently. This test tube contains something else.

Harry: Interesting. How do you know if a gas is hydrogen, Mr. Gerard?

Mr. Gerard: First of all, hydrogen is a colourless gas. And it has the lowest density. It is also dangerous.

Harry: Why is it dangerous?

Mr. Gerard: Oh, when it is mixed with oxygen, it is explosive.

Harry: I see. Is there any use for hydrogen?

Mr. Gerard: Yes, when hydrogen fuel cell is used in a car it does not give out carbon dioxide when it burns.

Harry: That is so cool! Perhaps, hydrogen is the answer to all our environmental woes!

Mr. Gerard: You could definitely say that.

Harry: How about oxygen?

Mr. Gerard: Oxygen is also a colourless gas. But as you know, it is essential for life. Also, even though it does not burn by itself, it supports combustion.

Harry: I know that oxygen is given to patients during surgical procedures.

Mr. Gerard: Yes, you are right. It has another very important use. Oxygen is mixed with acetylene to produce a very hot flame for welding.

Harry: I see. Can elements like hydrogen and oxygen mix with each other?

Mr. Gerard: Most definitely. You very own water is a compound made up of hydrogen and oxygen.

Harry: Oh yes. I remember you told us that. Are there any other compounds that are commonly used?

Mr. Gerard: Yes. Our table salt is a compound.

Harry: Made up of?

Mr. Gerard: Sodium and chlorine. The scientific name is sodium chloride.

Harry: Oh, I see. Any other compounds?

Mr. Gerard: Another compound is sodium hydroxide which is made up of sodium, oxygen and hydrogen.

Harry: I remember reading about that.

Mr. Gerard: Yes, you are right. Another common compound is copper sulfate.

Harry: Let me guess. It is made of copper, sulfur and oxygen?

Mr. Gerard: Excellent. You are right.

Harry: Mr. Gerard, just like elements have properties, compounds also may have properties, right?

Mr. Gerard: Definitely. Sodium chloride for example, is a white solid. It is not poisonous. And it dissolves in water, but does not react with water. I am talking about our table salt. So you know about the properties already.

Harry: Are these properties same as the individual components of sodium chloride? Which is sodium and chlorine?

Mr. Gerard: Not at all. Chlorine is gas that is greenish – yellow. And sodium is a soft metallic solid. It reacts violently with water. So, you see. The properties of the compound are very different from the properties of the individual elements that constitute it.

Harry: That is very interesting. Are compounds always formed from elements?

Mr. Gerard: There are a number of ways of producing a compound. Two elements can react to form a compound. For example, as we discussed earlier, carbon and oxygen, which are elements, combine to form the compound carbon dioxide. But there are other ways of producing a compound too.

Harry: What are the other ways?

Mr. Gerard: An element and a compound can react to form another compound.

Harry: Really? Can you give me an example of that?

Mr. Gerard: Yes, Harry. Calcium, which is an element, and water, which is a compound, can together form calcium hydroxide and hydrogen. Calcium hydroxide is a compound whereas hydrogen is an element.

Harry: Can two different compounds react to form other compounds?

Mr. Gerard: Yes. Iron chloride is a compound. Sodium hydroxide is also a compound. Together they form iron hydroxide and sodium chloride both of which are compounds.

Harry: These things are so very interesting, Mr. Gerard. Thank you so much. See you in class.