Science 8th grade
UNIT 7: Elements and compounds 7.2 Atoms and elements
Science 8th grade
UNIT 7: Elements and compounds 7.2 Atoms and elements
Chemical symbols
We have seen that there are more than 100 different elements including those that have been made in laboratories). Chemists use a shorthand way of referring to them. They have given cach clement a symbol.
• Sometimes the symbol is the first letter of the English name of the element. For example, the symbol for oxygen is O.
* Sometimes the symbol is the first letter of the English name of the element plus another letter from its name. For example, the symbol for helium is He.
• Sometimes the symbol is taken from the name of the element in another language. For example, the symbol for sodium is Na, from the old Latin name 'natrium'.
• The first letter of the symbol is always upper case. The second letter, if there is one is always lower case.
The four photographs show four different elements and their symbols.
|
|
|
|
Elements on Earth
Some elements, such as copper and gold, have been known for thousands of years. Others, such as radium and aluminium, have only been discovered more recently.
Some elements are very abundant (common) on Earth, and some are rare. The pie chart shows the approximate proportions of the various elements that are found in the Earth's crust.
Questions
$A+I$: 1) Which is the most common non-metal found in the Earth's crust?
$A+I$: 2) Which is the most common metal found in the Earth's crust?
Activity 7.2 (Researching an element)
Choose one element. Your teacher may suggest some good ones to choose.
Find out some facts about your element. For example:
• When was the element first discovered? Who discovered it, and how?
• What is the symbol for your element? Why does it have this symbol?
• Where is this element found? Is it rare or abundant on Earth?
• Do humans make use of the element?
Make a short presentation about your element, which you can give to the rest of the class.
Is water an element?
People believed that water was an element until about 1800. It was only then that a scientist passed electricity through water and found that it split up into two gases - hydrogen and oxygen.
Questions
$A+I$: 3) Suggest why people used to believe that water was an clement.
4) Explain why the experiment shown in the diagram proves that water is not an clement.
$A+I$: 5) a Name two gases that are found in air.
b: Is air an element? Explain your answer.