Physical changes, atoms and elements and the Periodic table by CGP

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Physical changes

Physical changes don't change the particles just the arrangement or their energy

Changes of state

When a solid is heated its particles gain more energy

This makes the particles move which weakens the forces that hold the solid together. This makes the solid expand

At a certain temperature, the particles have enough energy to break free from their positions. This is called melting and the solid turns into a liquid

When the solid is heated, again the particles get even more energy

This energy makes the particles move fast which weakens the forces holding the liquid together

At a certain temperature, the particles have enough energy to break the forces. This is called boiling and the liquid turns into a gas

Heating and cooling curves have flat bits

When a substance is melting or boiling, all the energy supplied from heating is used to weaken the forces between the particles rather than changing the temperature- hence the flat bits on the heating graph

When a substance is cooled, the cooling graph will show flat bits in a condensing and freezing points

This is because the force between particles get stronger

Atoms

Atoms are tiny, tiny particles

They're so small that you can't see them directly, this meant that no one knew much about them

Dalton was the first modern scientist to try and explain things about atoms According to the Dalton model:

All maters are made up of atoms

There are different types of atoms

Each element contains a different type

Elements

An element is a substance that contains only one type of atom

Quite a lot of everyday substances are elements

Elements have different properties for example copper is soft, bendy metal and oxygen is a colourless gas

All elements have a name and a symbol

There are over 100 different elements and writing their name out would take ages

So each element has a symbol- usually 1 or 2 letters

You can see each element on the periodic table

The periodic table

The periodic table shows all the elements that we have discovered

The first version of the periodic table was put together by a man who was named Mendeleev. It is thanks to him that the element with similar properties are arranged into vertical columns in the table

The vertical columns are called groups

The horizontal rows are called periods

If you know the properties of one element then you can predict the properties of the other elements which are in that group

You can use the periodic table to predict the patterns in reaction

In chemical reactions combine to form new substances

An element that's dead keen to combine with other elements are said to be very reactive (Group 1, 2 and 7 elements are all pretty reactive

Group 0 elements (the noble gases) are all extremely unreactive and they almost never take place in any chemical reactions

You can use the periodic table to predict patterns in chemical reactions. For example

Group 1 metals get more reactive as you go down the group. You can see this by how the group 1 metal reacts with water. When lithium reacts with water it fizzes. When rubidium reacts with water it explodes. This is because rubidium is much more reactive lithium