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Classifying Matter – Elements, Compounds and Mixtures

How is matter classified?

All matter can be classified as:

  • Elements
  • Compounds
  • Mixtures

Wait-a-second, why not classify matter as phases?

Some substances, like water can exist in more than one phase

  • Solid-ice
  • Liquid- water
  • Gas – steam

Some substances can also easily change from 1 phase to another.

So, classifying matter by phase is not very useful to us scientists, is it?

You can classify all matter using 3 questions

  • Can it be physically separated?
  • Can it be chemically separated?
  • Is it uniform throughout?

Here’s a cool flowchart that shows how you can use these questions in an easy and logical way to classify matter.

What are Elements?

Elements are the simplest form of a pure substance. They are represented by chemical symbols, consisting of one or two letters.

  • They cannot be broken into anything else by physical or chemical means.
  • The smallest particle of an element that has all the properties of that element is an atom. All atoms of an element are alike.
  • There are a total of 118 known elements, 94 of which occur naturally on Earth.
  • These elements are organized in a logical manner on a table called The Periodic Table.
  • These elements combine together to create millions of compounds.

Common Elements in the Earth’s crust

The 9 most common elements in the Earth’s crust are –

  • Oxygen ~ 46%
  • Silicon ~ 28%
  • Aluminum ~ 8.2%
  • Iron ~ 5.6%
  • Calcium ~ 4.2%
  • Sodium ~ 2.5%
  • Magnesium ~ 2.4%
  • Potassium ~ 2.0%
  • Titanium ~ 0.61%.

What are compounds?

Compounds are also pure substances, but they are made from more than one element.

  • They are usually the unions of two or more elements.
  • They can be broken into simpler substances by chemical means.
  • Example – Water (H2O) is a compound. It can be broken down into simpler substances – hydrogen and oxygen.

What are mixtures?

If a substance can be physically separated, it is classified as a mixture.

  • The substances in a mixture retain their individual properties.
  • Is this mixture uniform throughout?
    • No? Then it’s a heterogeneous mixture.
      • Examples are – trail mix, sand and pebbles mixed together, oil in water.
      • Suspensions are a type of heterogeneous mixture (fine sand in water)
    • Yes? Then it’s a homogeneous mixture. It looks the same throughout. Particles are very small and look well-mixed together. These can be classified into –
      • Examples are – corn oil, white vinegar, sugar solution (mixed well so all you see is a clear liquid).
      • A colloid is a homogeneous solution with intermediate particle size. So if you shone a beam of light through it, the particles would be visible. Milk, fog, and jello are examples of colloids.

 

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