Do We Have Evidence?
 How Do We Know that…..
 Everything is made of atoms (particles)
 They are in perpetual motion
 They attract at a short distance
 They repel each other when squeezed
together
THE PARTICULATE NATURE OF
MATTER
Objectives :
(a) Describe the solid, liquid and gaseous
states of matter and explain their
interconversion in terms of the kinetic
particle theory and of the energy changes
involved.
(b) Describe and explain evidence for the
movement of particles in liquid and gases.
Matter - a Particle Explanation
 Matter is anything that occupies space and
has mass.
 Matter is made up of small particles -
Democritus
By convention there is color,
by convention sweetness,
by convention bitterness,
but in reality there are atoms and space.
-Democritus
460-371 BC
The Kinetic Particle Theory
The Kinetic Particle theory of matter states that
 all matter is made up of tiny particles
called atoms
 all particles are in constant random motion
 There are both attractive and repulsive
forces between particles – it depends on
the distance between the particles if
attractive or repulsive
Particulate Nature of Matter Evidence
 From Diffusion experiments…
When a few drops of bromine
are placed into a gas jar of air,
the red-brown bromine vapour
spreads slowly upwards until
the whole jar is filled with a
uniform brown vapour.
Particulate Nature of Matter Evidence
 From Diffusion experiments…
…observations can be
explained if we accept
the idea that the
substances are made up
of small particles in
constant motion.
Particulate Nature of Matter Evidence
 From Diffusion experiments…
..and during diffusion,
the bromine particles
move into the spaces
between the air particles
while the air particles
move into the spaces
between the bromine
particles..
Particulate Nature of Matter Evidence
 From changes in volume - mixing water & alcohol
…observation can be explained
if we agree that water and
ethanol are made of particles.
50 cm3 of water mixed with
50 cm3 of alcohol gives
98 cm3 of mixture
There are empty spaces between
the ethanol particles. The
water particles move into these
spaces.
Particulate Nature of Matter Evidence
 From changes in volume - mixing water & alcohol
By convention there is color,
by convention sweetness,
by convention bitterness,
but in reality
there are atoms and space.
-Democritus
460-371 BC
…observation can be explained
if we agree that water and
ethanol are made of particles.
There are spaces between the
ethanol particles. The water
particles move into these
spaces.
We Gather Some Evidence….
 How did the perfume particles reacah your
nose?...Whiteboard your thoughts
 Why did the food color particles mix faster in
the hot water than the cold? .. Whiteboard
your thoughts
 Why did the contents of the volumetric flask
shrink when the salt dissolved?..Whiteboard
your thoughts
Particulate Nature of Matter Evidence
 From changes of state
Particulate Nature of Matter Evidence
 Others - dissolving, fusing of metals
The Particles of Matter
Atoms
Molecules
Ions
The 3 States of Matter
Property
solid
liquid
gas
Definite mass



Definite shape



Definite volume



The Kinetic Particle Theory
The Kinetic Particle theory of matter states
that
 all matter is made up of tiny particles;
 all particles are in constant random
motion
 Attractive and Repulsive forces
between particles explain much of their
behavior.
The 3 States of Matter
The 3 States of Matter
Property
Packing of particles
Arrangement of
particles
Movement of
particles
Attractive forces
between particles
solid
liquid
closely packed
Orderly
vibrate and
rotate about
fixed
positions
very strong
gas
far apart
Not orderly
Not orderly
vibrate and
slide over one
another
move rapidly
and at
random in any
direction
less strong
almost no
The Solid State
Property
Explanation
•Definite shape
•Definite volume
particles cannot move
freely; can only vibrate
about fixed positions
• Cannot be
compresssed
Particles are packed
very closely together
The Liquid State
Property
Explanation
• No definite
shape
particles can slide over one
another
• Cannot be
compresssed;
has fixed
volume
Particles are packed
close together
The Gaseous State
Property
• No definite
shape or
volume
• Can be
compresssed
Explanation
particles can move about
rapidly and randomly in any
direction as forces between
particles are weak
Particles are far apart,
with a lot of empty
space between them
Changes of State
GAS
SOLID
melting
LIQUID
freezing
Melting - in terms of Kinetic
Particle Theory
• When a solid is heated, heat energy is absorbed. This
causes the particles to gain kinetic energy and to vibrate
faster.
• At a certain temperature (melting point, the vibrations
become so violent that the particles are able to overcome
some of the attractive forces between them and break
away from each other.
The solid then becomes a liquid. Melting occurs.
Freezing - in terms of Kinetic
Particle Theory
• When a liquid is cooled, heat energy is released. This
causes the particles to lose kinetic energy and to vibrate
slower.
• At a certain temperature (freezing point, the vibrations
become so slow that the particles are unable to overcome
the attractive forces between them and are drawn towards
each other in orderly and fixed positions.
The liquid then becomes a solid. Freezing occurs.
Boiling - in terms of Kinetic
Particle Theory
• When a liquid is heated, heat energy is absorbed. This
causes the particles to gain kinetic energy and move
faster.
• At a certain temperature boiling point), the vibrations
become so violent that the particles throughout the
liquid are able to break away from the forces holding
them together.
The liquid then becomes a gas. Boiling occurs.
Sublimation - in terms of
Kinetic Particle Theory
• When the solid is heated, heat
energy is absorbed. Particles
gain kinetic energy and
move faster.
• At a certain temperature the
vibrations become so violent
that the particles break free
completely from each other,
and move randomly.
The solid then becomes a gas
directly. Sublimation occurs.
Heating Curve
temperature (ºC)
melting
starts
melting
point
melting
completes
SOLID + LIQUID
LIQUID
SOLID
temperature remains
constant. Why?
Heat energy absorbed by the
particles is used to overcome
the forces of attraction holding
the particles together in their
fixed positions.
time from start (min)
Cooling Curve
Heat loss due to cooling is
exactly balanced by the heat
energy liberated as the particles
attract one another to form a
solid.
temperature (ºC)
LIQUID
freezing point
(=melting point)
for pure
substances
temperature
remains constant.
Why?
SOLID
LIQUID + SOLID
freezing
starts
freezing
completes
time from start (min)
Evaporation vs Boiling
Similarity : Both involve the change of state
from liquid to gas.
Differences :
Boiling
Evaporation
Takes place at boiling
point of the liquid
takes place throughout
the liquid
Takes place at any
temperature below
takes place at the
surface of the liquid
very fast process
very slow process
Predicting physical states
Substance X has m.p. -460C and b.p. 1670C.
What is its physical state at
(i) room temperature (ii) -100C (iii) -500C ?
SOLID
LIQUID
- 460C 250C
sl
GAS
1670C
lg