Science 8th grade
UNIT 7: Elements and compounds 7.1 Atoms
Science 8th grade
UNIT 7: Elements and compounds 7.1 Atoms
What are atoms?
Over 2000 years ago a Greek philosopher called Democritus suggested that everything was made up of tiny pieces.
Democritus suggested that, if you could keep on cutting up a substance into smaller and smaller pieces, you would eventually end up with a very small piece that could not be cut up any more.
Democritus called his tiny pieces of matter atoms. Atom means 'cannot be divided'.
We now know that atoms really do exist. Today, we can even see some of the larger kinds of atoms, using very special microscopes called scanning tunnelling microscopes. The photograph shows the atoms in some carbon nanotubes. ('Nano' means very, very small.)
Different kinds of atoms
There are many different types of atoms. Scientists have discovered 94 different kinds of atoms that occur naturally in the Universe. Another 24 kinds of atoms have been made in laboratories.
Some substances are made up of just a single kind of atom. A substance that is made of just one kind of atom is called an element.
For example, carbon is made only of carbon atoms. Gold is made only of gold atoms. Silver is made only of silver atoms. Carbon, gold and silver are examples of elements.
Each type of atom has different properties. This is why different clements have different properties.
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Questions
1) What are atoms?
2) If there are 94 different kinds of naturally occurring atoms, how many different naturally occurring elements are there?
Atoms joining together
Some substances are made up of individual atoms. For example, a piece of gold is made up of millions of individual gold atoms. Neon - which is a gas - is made of individual neon atoms.
Other substances are made up of little groups of atoms. The atoms join together in groups of two or more.
A group of atoms joined tightly together is called a molecule.
Some elements are made up of molecules. For example, in oxygen the atoms are joined together in pairs. A molecule of oxygen is made from two atoms of oxygen joined together.
Sulfur molecules are made up of eight sulfur atoms joined together. They can be joined in slightly different ways.
Activity 7.1 (Modelling oxygen molecules)
1) Imagine that you and all the other students in your class are oxygen atoms.
2) Form into an oxygen molecule by linking arms with a partner.
3) You are a gas so spread out among the other oxygen molecules and behave as gas molecules at room temperature.
4) Imagine the temperature has dropped so low that the oxygen has become a liquid. Change your arrangement and behaviour to model this.
5) Imagine that the temperature is even lower and that the oxygen has solidified. Change your arrangement and behaviour to model this.
Questions
${A_1}$: Describe and explain how molecules of oxygen gas behave when the room temperature falls.
${A_2}$: Describe and explain how molecules of oxygen behave when the temperature is so low that the oxygen becomes a liquid.
${A_2}$: Describe and explain how molecules of oxygen behave when the temperature is so low that the oxygen solidifies.