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Chemistry

Chemistry explores what substances are made of, how their particles are arranged and how substances change. A particle model can explain something you cannot see directly.

How does a particle model explain the difference between a mixture and a new substance?

A close view of blue copper sulfate crystals with flat faces and angular edges.
Copper sulfate crystals: visible crystal faces are a material structure, not a photograph of individual atoms.Дарья Могилевцева · Source · CC BY 4.0

Atoms, molecules and ions

An atom is a unit of a chemical element. A molecule contains two or more bonded atoms and is electrically neutral. An ion has an electrical charge. These terms are not interchangeable: not every substance consists of separate molecules. Choosing precise words helps prevent a model from creating a misconception.

Arrangement matters

Two materials can contain some of the same elements and still behave differently because their particles are arranged or bonded differently. A mixture brings substances together without necessarily making a new substance. In a chemical reaction, atoms are rearranged as substances change; the atoms are not simply used up and lost.

Models need a key

Coloured circles can stand for different atoms, but the colours are a code you choose, not the atoms’ real colours. Lines may represent bonds. Include a key and say what the model leaves out, such as three-dimensional arrangement or particle size. A photograph of crystals shows a material’s appearance, not individual atoms.

Only if you feel like trying

Rearrange atoms on paper

  1. Draw two pairs labelled H–H and one pair labelled O–O. Explain that H and O are different elements.
  2. Redraw the same four H labels and two O labels as two H–O–H groups.
  3. Count before and after. What stayed the same, and what changed in the arrangement?

Optional symbolic model of a reaction, not an experiment. Do not mix, taste or heat chemicals; the crystal photograph is not an invitation to handle copper sulfate.