You can recognize the three phases of water in practice
You can describe the three phases in which water can occur using the particle model
You can use the particle model to explain why ice and many other solid substances have characteristic crystal structures
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Three phases
What do we see in these pictures?
Rain, mist, snow, hail and dew all look very different
But they all consist of one substance, water!
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Three phases
Water, like many other substances can exist
in three different states, also known as phases
As a solid substance - ice
As a liquid - water
As a gas - water vapour
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solid
Other examples of solid substances are wood and bricks
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Three phases
Other examples of liquids are gasoline and alcohol
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Three phases
Other examples of gasses are oxygen (O2) and carbon dioxide (CO2)
These gasses are in the air, we can't see them
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Phases in the particle model
You can't see how the molecules of a substance move
But you can try to picture it in your head
You can imagine how to molecules move around and how they affect one another
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Phases in the particle model
In physics and chemisty the particle model is widely used
In this model a substance is always made up of the same molecules, no mather the phase
A substance can exist in different phases because the molecules can move in various ways
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phet.colorado.edu
Slide 11 - Link
Phases in the particle model
Now we know that in solid substances, all molecules have fixed positions, they can still move, but only by vibrating back and forth.
This is why ice cubes also have a fixed shape
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Phases in the particle model
In liquids molecules don't have a fixed position. they can move around past other molecules. Water drops don't have a fixed shape because of this. The molecules do remain together as close as possible.
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Phases in the particle model
Molecules in gasses are able to move freely. They spread out to fill the space the gas is in. The distance between molecules is large.
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Crystals
Snow is made up of ice crystals which can have
different shapes
But all those shapes exist of the same six-sided
structures
This is called a crystal structure
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Crystals
The particle model lets you explain why crystals have fixed shapes.
Because all molecules in a substance are identical, they can 'stack' in regular patterns , this creates a crystal lattice (kristalstructuur) in which every molecule has a fixed position
Lesson duration is: 45 min
