revision summary notes, elements , compounds , mixtures, separating techniques for mixtures
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Course
IGCSE , chemistry, revision
Institution
IGCSE , Chemistry, Revision
Book
Chemistry
The document contains simplified and to-the-point explanations of the concept. Revision these would be enough to cover the topic within half time and will guarantee a good grade.
What is meant by an element? A compound, a mixture and a molecule.
These ideas are important in Chemistry, so it is essential that you understand them.
Let us start by looking at elements.
The periodic table shows us all the elements and there are around one hundred of them.
Here is the periodic table and you are given a copy of this in your exam.
Each of these symbols represents a different element.
For example, we have got the element sulfur over here. This brings us the definition of an
element which you need to learn. In an element, all of the atoms are the same.
So for example, this shows the atoms in a sample of magnesium.
You can see that all of the magnesium atoms are the same.
Here are the atoms in a sample of sulfur.
Again, all of the sulfur atoms are the same.
Each element has a symbol and every symbol starts with a capital letter.
So the symbol for magnesium is capital M followed by a lower case g.
, The symbol for sulfur is simply capital S.
Compounds
If we take atoms of magnesium and atoms of sulfur, and chemically combine them like this then
we have got a compound.
Magnesium sulfide
Compounds contain two or more different elements chemically combined. This compound is
called magnesium sulfide. In compounds, the elements combine in a fixed proportion.
So for example in magnesium sulfide, we always have one atom of magnesium
Chemically combined with one atom of sulfur.
Another key fact is that compounds usually have totally different properties to the elements that
they are made from. As you can see, magnesium is a shiny metal and sulfur is a yellow solid.
However, magnesium sulfide is a white crystal.
Separation of element in compound
If we want to separate a compound back into its elements,
Then we need to use a chemical reaction and that is not always easy to do.
Mixtures.
In a mixture we have different elements or compounds but they are not chemically combined.
This shows a mixture of magnesium atoms, sulfur atoms and magnesium sulfide.
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