4 1 revisiting the particle model - aais

Chapter 4 Elements, mixtures and compounds
Sunday, April 5, 2020
By
Sir. Muhammad Abdul Mageid
Chemistry Teacher

Contents
4.3 Diffusion
4.1 Revisiting the particle model
4.4 Atoms, molecules and elements
4.2 Gas Pressure
4.7 Elements and compounds
4.5 Chemical symbols and formulae
4.8 Forming compounds from elements
4.6 introducing the periodic table
4.9 Investigating elements ,mixtures and compounds

Chapter Student Book topic Framework point
Chemistry:
Chapter 4:
Elements,
Mixtures and
Compounds
4.1 Revisiting the particle model Show how the
particle theory of
matter can be used
to explain the
properties of solids,
liquids and gases,
including changes
of state

Everything is Made of Particles
Made of particles
 Rock, air, and water look very different. But they
have one big thing in common: they are all made of
very tiny pieces, far too small to see.
Particles on the move
 In rock and other solids, the particles are not free to
move around.
 But in liquids and gases, they move freely. As they
move they collide with each other, and bounce off in
all directions.
 So the path of one particle, in a liquid or gas,
could look like the opposite figure:

States of matter :
Solids, Liquids, and Gases
What’s the difference?
 It is easy to tell the difference between a solid, a liquid and a gas:

Sunday, April 5, 2020Sunday, April 5, 2020
 A solid has a fixed
shape and a fixed
volume.
 Can not flow.
 Can not be
compressed
 Particles are lined up
next to each other
 They are fixed in
position but do
vibrate
 A liquid has no fixed
shape and a fixed
volume.
 Can flow.
 Very difficult to
compress
 Particles are still
very close but can
slip and slide over
each other
 A gas has no fixed
shape and spreads
out to fill its container
 Can flow.
 Easily compressed
 Particles move
rapidly around at
random and there is
lots of space within
the gas

The Particles in Solids, Liquids, and Gases
State How the particles are arranged Particles Diagram
Solids
The particles in a solid are arranged in a
fixed pattern or lattice. Strong forces hold
them together. So they cannot leave their
positions. The only movements they make
are tiny vibrations to and fro.
Liquids
The particles in a liquid can move about and
slide past each other. They are still close
together, but not in a lattice. The forces that
hold them together are weaker than in a
solid.
Gases
The particles in a gas are far apart, and they
move about very quickly. There are almost
no forces holding them together. They collide
with each other and bounce off in all
directions.

Change Definition Type of process
Melting
The change of matter from solid state to
liquid state by heating [absorbing energy]
Endothermic
process
Boiling/
Evaporation
The change of matter from liquid state to
gaseous state by heating [absorbing energy]
Endothermic
process
Condensation
The change of matter from gaseous state to
liquid state by cooling [releasing energy]
Exothermic
process
Freezing /
Solidifying
The change of matter from liquid state to
solid state by cooling [releasing energy]
Exothermic
process

Explanation of Changing state[ Using the particle theory]
 Boiling When a liquid is heated, its particles get more energy and move
faster. They bump into each other more often, and bounce further apart.
This makes the liquid expand. At the boiling point, the particles get
enough energy to overcome the forces between them. They break away
to form a gas:
 Evaporation Some particles in a liquid have more energy than others.
Even well below the boiling point, some have enough energy to escape
and form a gas. This is called evaporation. It is why puddles of rain dry
up in the sun.
Heat Energy
Heat Energy at
melting point

4.1 Summary Quistions
1. Using the idea of particles, explain why:
a- liquids flow but solids do not flow
b- solids have a fixed shape but liquids and gases take up
the shape of their containers
2. Define the following words:
a- boiling b- melting c- condensing d- freezing
3. Using the particle theory , explain what happens when:
a- we heat a solid until it melts
b- we heat a liquid until it boils

4.1 Past Papers Questions
The following diagram shows the three states of
matter and how they can be interchanged
i- Name the changes A , B , C and D
ii- Which of the changes A , B , C or D will involve:
1) an input of heat energy ?
2) an output of heat energy ?

4 1 revisiting the particle model - aais

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