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 What is an atom? If we break all materials down into the smallest particle that can exist by itself, then what we have is atoms. Atoms are the smallest particle of all matter that can exist by itself.   How small are atoms? Atoms are so small that we can not use cm or even mm to measure there size, we use nm (nanometers) 1nm = 0.000000001m The diameter of a sodium atom is 0.4nm. You could fit approximately 400000000000000000000000 of them on the surface of a 2€ coin.

 Do you know your symbols? It is very useful to know the names and symbols of the common elements. Internet site link Learn the elements and their symbols with these interactive games.   Activity Useful for revision and finding your way around the periodic table. Complete the sheet (pdf download) for the first 20 elements Hydrogen to Calcium.

PHYSICAL SCIENCE

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Atoms and Ions

The structure of an atom

The atomic particles

There are three well known particles in the atom. The proton, neutron and electron. The table below gives the relative position, mass and charge of each particle.

 Particle Relative Postition Mass Charge Proton Nucleus 1 1 Neutron Nucleus 1 0 Electron Orbits 0 -1

How many protons, neutrons and electrons does each atom have?

From the periodic table you will see that each element is represented in the following way:

 represents the symbol of the element. is the mass number of the element which is equal to the number of protons + neutrons found in the nucleus of each atom of that element. is the atomic number of the element which is the number of protons found in each atom of that element.

All atoms are neutral so they have equal numbers of protons and electrons

We can use this information to calculate the number of protons neutrons and electrons found in each atom of a particular element.

Example : This represents the element carbon.

 A = 12 which means it has 6 protons, hence 6 electrons Z = 6 Which means it has a total of 12 protons AND neutrons which means it has: 12 - 6 neutrons = 6

The number of neutrons is equal to A - Z

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