Particles
Particle Theory & States of Matter
Matter
Anything that has mass and takes up space (ie. everything)
States of matter
Solid, liquid & gas
Solid
Liquid
Gas
Shape
Fixed
Varying
Varying
Volume
Fixed
Fixed
Varying
Compressing
No
No
Yes
Spacing
Close
Close
Far apart
Arrangement
Regular
Irregular
/
Movement
Vibrate at fixed positions
Move around each other
Move freely in all directions
The particle theory
Matter is made out of particles.
Particles are very small.
Different matter is made out of different particles.
Particles come in different masses and sizes.
Particles are constantly moving.
There is space between each particle.
Basic ideas
Democritus
If matter keeps getting divided into smaller and smaller pieces, there would eventually be a point where the pieces are too small to be further divided. Those pieces are particles.
Robert Brown
Pollen grains move randomly on their own in still water
The motion of the pollen grains would later be called Brownian motion
Einstein
Brownian motion is caused as water particles hit pollen grains in different directions from time to time.
Evidence of particle existence
We can smell perfume from a balloon with a few drops of perfume inside (as the particles can leave the balloon walls through the small gaps and go outside).
When 50cm3 of water and alcohol are mixed, the mixture doesn’t add up to 100cm3 (as the smaller water particles may get into spaces between the larger alcohol particles)
Dissolving
Explanation using particle theory
Sugar is made out of sugar particles
Sugar particles separate and mix with the water particles
Sugar and water particles are moving. They soon become evenly spread out.
Trivia
Mass is conserved in dissolving, while volume changes.
Melting VS dissolving
Melting
Dissolving
1 type of particle involved
2 types of particles involved
Particles can move around
Particles separate and mix
Thermal Expansion & Contraction
When a substance is heated, the particles move faster and are further apart. The volume increases in size as a whole.
When a substance is cooled, the particles move slower and are closer together. The volume decreases in size as a whole.
Degree of expansion
Solids
Particles are tightly packed
Have great attraction between each other
—> Don’t expand much
Gases
Particles are loosely packed
DON’T have great attraction between them
—> expand the most
Daily applications
Thermometer
Colored alcohol/mercury expands/contracts as the temperature changes. The liquid level changes and the temperature is shown
Fire sprinkler
A fire sprinkler has a glass tube filled with a liquid. When there is a fire, the heat from the fire causes the liquid to expand, breaking the glass tube. Water flows out from an opening
Gas pressure
Gas Pressure
The exertion of force upon a surface by gas particles
Measured by the gas gauge w/ the units pascal (PA) or newtons per m2 (N/m2)
Explanation from particle theory
Gas particles can move freely in all directions, constantly hitting the walls and push against them. The total strong push is gas pressure
When temperature increases/volume decreases
Particles move faster and hit walls more frequently
Gas pressure increases
Applications
Aerosol cans — Pressured gas is filled in the can. The gas pressure pushes the liquid into the tube and sprays out the liquid.
Airbags — In an accident, the airbag of the car inflates. The gas pressure from the airbag stops the driver to protect him.
Bicycle suspension — Some bicycle suspensions have gas chambers holding high pressure gas, absorbing shock from a bumpy road. It is large enough to support the cyclist’s weight
Density
Density
Density = mass/volume
The unit of density is g/cm3 or kg/m3
Tells us how much material is packed into a unit volume
When sth is heated, the volume increases but the mass remains unchanged. So, the density decreases
The Principle of Floating
A substance with a lower density floats on one with a higher density
Questions
Water exists in liquid state at room temperature because
The boiling point of water is higher than room temperature
The melting point of water is higher than room temperature
The freezing point of water is higher than room temperature
The boiling point of water is lower than room temperature
Answer
a
Since room temperature is 25 Degrees Celsius and the water boiling point is 100 Degrees Celsius, the water doesn’t boil as the temperature is lower than that of the boiling point.
Daily examples of condensation
(i) Formation of ice
(ii) Formation of water droplets on the surface of a bottle of cold drink
(iii) Formation of clouds
(iv) Steam giving out from the surface of a bowl of hot soup
a. (i) and (ii) only
b. (i) and (iii) only
c. (ii) and (iii) only
d. All of the above
Answer
c
Condensation is steam turning into water.
In (ii), the water vapor in the air turns into water.
In (iii), water evaporates and condenses in the air, forming clouds.
Which statements about freezing are correct?
(i) It’s a change of state from liquid to solid
(ii) It’s a change of state from solid to liquid
(iii) It occurs at a fixed temperature for certain substances under a fixed pressure
(iv) It occurs at fixed temperatures for all substances under a fixed pressure
a. (i) and (ii) only
b. (i) and (iv) only
c. (ii) and (iii) only
d. (ii) and (iv) only
Answer
a
When ice is taken out of a fridge, some white smoke appears. This is because
The water vapor around starts condensing
The ice starts evaporating
The ice starts melting
The evaporated water starts freezing
Answer
d
The water vapor around the ice freezes, so the water vapor turns to ice quickly, turning white.
Which of the following are evidence of particles’ existence?
(i) We can smell flower’s scent from a distance
(ii) We can observe bright particles moving randomly in the smoke cell under microscope
(iii) We can dissolve sugar in water
a. (i) and (ii) only
b. (i) and (iii) only
c. (ii) and (iii) only
d. all of the above
Answer
d
(i) shows that particles are constantly moving
(ii) shows that they are very small (and exist)
(iii) shows that different particles have different sizes and masses (to mix together)
Probably volume of the mixture when 50cm3 water 50cm3 alcohol is mixed together:
60 cm3
98 cm3
100 cm3
102 cm3
Answer
b
Alcohol and water particles have different sizes. So they can go into small gaps. The volume isn’t the same.
What happens during the freezing of water?
Its temperature decreases and its volume increases
Its temperature decreases and its volume decreases
Its temperature remains unchanged and its volume increases
Its temperature remains unchanged and its volume decreases
Answer
c
When changing states, the temperature doesn’t change.
It has to be 0 degrees for BOTH the water and the ice to change states, so its temperature is unchanged.
When it reaches the temp. of 4 Celsius degrees it’s molecules order in a structure that is less dense than liquid water ( increasing it’s volume ) ,that’s the reason why ice floats above liquid water.
What are similarities and differences of solids & liquid?
Answer
Similarities: Particles are close together
Differences: Particles are arranged regularly in solids, but irregularly in liquid (as it can change shape)
Why do solids have a hard exterior?
Answer
The particles arranged themselves closely and regularly and cannot be compressed further.
What are the differences of liquid and gas?
Answer
The particles in liquid are close together whist the particles in gas are far apart
Compare the movement of particles in solids, liquid, and gas respectively.
Answer
Solid: Particles only vibrate about fixed positions
Liquid: Particles can move around each other
Gas: Particles can move freely
Which state of matter expands the most?
Answer
Gas. Gases expand much more than the liquids and the solids. The greater the attraction between the molecules, the smaller the expansion will be.