Chapter 4.pdf

The temperature at which a solid turns into a liquid is called
the melting point. For example, the melting point of water is
0°C. The reverse process, freezing, occurs at the freezing point.
The melting point and the freezing point are always the same
temperature. Similarly, the temperature at which a liquid turns to
a gas is called the boiling point. The boiling point is the same
temperature as the condensing point, the temperature at which a
gas changes into a liquid.
The Particle Theory of Matter
The particle theory of matter is a way to describe the structure
of matter and its behaviour (Figure 4.5). Matter can be broken into
smaller and smaller pieces. Is there a limit to how many times a
piece of graphite from a pencil can be divided and still be graphite
The answer is yes. The smallest possible pieces of graphite are
particles. The particle theory of matter explains how this works.
• All matter is composed of very tiny objects called
particles. These particles are too small to be seen, even
with a powerful light microscope.
• All particles have spaces between them. The distances
between the particles change for different states of matter.
For example, particles in a liquid have more space between
them than the particles in a solid of the same substance, but
particles in a liquid have less space between them than
particles in a gas.
• Particles present in matter are always in motion. They
may be vibrating back and forth, as in a solid, or moving in
all directions, as in a gas. In a liquid, particles stay close
together but can slide past one another.
• The particles in a substance attract each other. The
amount of attraction is different for different kinds of
particles. In iron, which is a very hard solid at room
temperature, the particles strongly attract each other. In
water, which is a liquid at room temperature, the particles
of water can slide past each other because the attractions
between them are not very strong.
For a given substance such as water, the state it is in is related
to its temperature.
solid
strong force
close together
liquid
weaker force
farther apart
gas
very weak force
very far apart
Figure 4.5 Particles are arranged
differently in a solid, a liquid, or
a gas.
Matter has physical and chemical properties.
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