Electrons and Electron Shells

In lesson number 7 we found out that atoms are made out of three types of particle. The particle found on the outside of the atom are called electrons.

Each type of atom has a different number of electrons on its outside. We know that: Hydrogen has 1 electron Oxygen has 8 electrons Copper has 29 electrons The electrons are always on the outside of the atom: the rest of the particles are in the centre of the atom (its nucleus). when atoms bump into each other it is the electrons from different atoms that meet. We can guess that when chemical reactions happen between atoms it is the electrons that are involved.

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Fill in these missing words ...

Atoms are made from different types of particle. On the outside of an atom you can find a number of . The middle of the atom is called the . Different types of atom have different numbers of on the outside. For example has only 1 electron on the outside.

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The electrons form layers (or shells) around the nucleus. The first layer can only hold two electrons; the next layer can hold a maximum of eight electrons; and the next layer can only hold 8 electrons. The picture shows the electrons in a sodium atom. Sodium has 11 electrons: the first layer fills up with 2 electrons - there are 9 left over the next layer fills up with 8 electrons - there is 1 left over the last electron is all alone in the next layer Sodium is in column 1 of the periodic table because it has 1 electron in its outside layer.

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Now answer these questions:

1. How many particles are there in an atom ? one two three four
2. Which particles are on the outside ? electrons protons proteins neutrons
3. What two particles are in the nucleus ? proteins and fats protons and neutrons 2 protons preutrons and notons
4. Electrons are found around the nucleus in layers, or what ? shells coats circles
5. How may electrons are there in a hydrogen molecule ? four three two one
6. How many electrons are there in a sodium molecule ? one eleven twenty one thirty one
7. How many electrons are in the first layer (shell) of a sodium atom? none one two three
8. How many electrons are in the second shell of a sodium atom ? two four six eight
9. How many electrons are in the last shell of a sodium atom ? none one two three
10. Sodium is in which column of the periodic table ? none one two three

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Now fill in these missing words ...

Different atoms have numbers of atoms. Protons and neutrons are on the inside of the nucleus and the electrons are on the . The electrons are arranged into layers, or , around the outside of the nucleus.

Atoms can have a maximum of electrons in the first shell and in the second and third shells.

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