Particle Theory Flashcards
The main points of the particle theory:
1) All matter is made up of particles.
2) Particles are very small.
3) Different matter is made up of different particles.
4) Different particles have different sizes and masses.
5) Particles are moving all the time.
6) There are empty spaces between particles.
Explain Brownian motion of pollen grains in water.
Water is made up of very small water particles. The water particles are much smaller than the pollen grains and they are moving in different directions. They hit the pollen grains in different directions from time to time. Therefore, the pollen grains are moving randomly in zigzag paths.
Particle model of solids:
The particles are close together and arranged regularly. They cannot move from one position to another, but can only vibrate about fixed positions.
Particle model of liquids:
The particles are close together but arranged irregularly. They can move around each other.
Particle model of gases:
The particles are far apart. They can move freely in all directions.
What is the particle model used for?
It is used by scientists to describe the arrangements and movements of particles in the three states of matter.
Explain the dissolving of sugar in water.
When sugar dissolves in water, the sugar particles separate and mix with the water particles. The sugar particles are too small to be seen and therefore the sugar seems to disappear. However, the sugar is still there. This can be easily detected from the sweet taste of the solution formed.
Why is the volume of sugar solution slightly less than the total volume of sugar and water before dissolving?
Based on the particle theory, there are spaces between particles. When sugar dissolves in water, the sugar particles separate. The smaller water particles fit into the spaces between the bigger particles. Therefore, the volume of the solution is slightly less than the total volume of the sugar and water before dissolving.
Why does the mass of sugar solution remain unchanged after dissolving?
Unlike volume, mass remains unchanged in dissolving. Although the sugar particles separate, they are still in the water. The total number of the sugar particles and water particles remains the same. Therefore, the mass of the sugar solution is equal to the total mass of the sugar and the water before dissolving. In other words, mass is conserved in dissolving.
Explain thermal expansion and contraction.
From the movement of particles, we can understand the change in the size of a substance when it is heated or cooled. When a substance is heated, its particles move faster. Therefore, the particles are further apart and the substance as a whole increases in size. Similarly, when a substance is cooled, its particles move slower and become closer together, causing the substance as a whole to decrease in size.
Explain density.
Objects made of different substances have different masses, even though they have the same volume. This is because different substances have different densities. Density is the mass per unit volume of a substance and its unit is g/cm3 or kg/m3. For the same volume, substances with higher density have greater mass.
Explain floating and sinking.
Whether an object floats or sinks in a liquid depends on density. An object floats in a liquid if its density is lower than that of the liquid. On the other hand, an object sinks in a liquid if its density is higher than that of the liquid.
Explain the effect of temperature of temperature on density by using the particle theory.
The particles of a substance move further apart when the substance is heated. This causes the substance to expand. Since the volume of the substance increases while the mass remains unchanged, the density of the substance decreases. Similarly, when a substance is cooled, its particles move closer together. This results in a smaller volume of the substance. Therefore, the density of the substance increases.
How does a hot air balloon work?
When the air inside a hot air balloon is heated, the air particles move faster and become further apart. The air expands so its density decreases. The overall density of the balloon becomes lower than the density of the air around it and thus the balloon rises.
How does a thermostat help control the temperature of an electric iron?
When the iron is too hot, the bimetallic strip bends upwards. The bimetallic strip no longer touches the contact and the circuit breaks. The iron is thus switched off. When it cools down, the bimetallic strip straightens and the bimetallic strip touches the contact. Now the circuit is closed. This switches on the iron again.
