Kinetic Particle Theory (Kinetic Model of Matter)

You are expected to… describe the three states of matter and explain their inter-conversion in terms of the kinetic particle theory. show understanding that Brownian motion provides evidence for the kinetic molecular model of matter. explain everyday effects of diffusion in terms of particles, e.g. the spread of perfumes and tea/coffee grains in water. describe qualitatively the molecular structure of solids, liquids and gases, relating their properties to the forces and distances between molecules and to the motion of the molecules.

Recall: What is Matter? Objects that have mass and occupy space are called matter.

Question: Is this glass bottle empty? No. It is filled with air!

Recall: How do we classify matter? What are the three states of matter? Do you know that there are more than three states of matter? Plasma Bose-Einstein condensate

Recall: Properties of each state of matter Solids Liquids Gases Shape fixed shape no fixed shape Volume fixed volume no fixed volume Ability to be compressed incompressible compressible

Let’s see what the philosophers have to tell us… What is matter made of? Let’s see what the philosophers have to tell us…

Democritus “…if one were to break up matter into smaller and smaller piece, there would come a point when it could no longer be divided further.” He called this smallest indivisible bit of matter ‘atom’ (from the Greek word atomos which means indivisible). Greek Philosopher (460 B.C. – 370 B.C.)

Aristotle “Matter has a continuous composition and that it can be broken down into smaller and smaller pieces forever.” Aristotle was highly regarded and most people followed his school of thought about the nature of matter Philosopher (384 B.C. – 322 B.C.)

Democritus or Aristotle? Who is right? Democritus or Aristotle? Let’s vote! Let’s see who’s right…

Brownian Motion

Brownian Motion Think, Pair, Share Describe the motion of pollen grains in water and the smoke particles in air. Moving constantly in a random or irregular motion What caused these motions? Pollen grains and smoke particles were bombarded by water molecules and air particles respectively which themselves were moving constantly and randomly.

Brownian Motion The constant and random motion of small solid particles in fluids (liquids and gases) is called Brownian motion. Brownian motion provided the evidence of molecular motion & proved the existence of particles that cannot be observed with a normal microscope. Just for info: Brownian motion is first observed in 1827 by Robert Brown. Through the microscope, he observed the motion of pollen grains suspended in water. However, he was unable to provide an explanation for Brownian motion.

Particles that make up of matter Using a scanning tunneling microscope (STM), scientists are now able to observes the particles that make up matter. Gold atoms

Particles that make up of matter Iron on Copper

So, who’s right? In conclusion… Matter is made up of discrete (separate not continuous) particles which are in constant and random motion. In other words… Democritus’ proposal that matter is made up of tiny particles is right! Democritus (460 B.C. – 370 B.C.)

Kinetic Model of Matter (Kinetic Particle Theory) Based on observations, a model (Kinetic Model of Matter) which explains the nature of matter was proposed. The Kinetic Model of Matter (Kinetic Particle Theory) states that matter is made of tiny discrete particles (atoms or molecules), which are in constant and random motion. Energy due to movement = Kinetic energy

Ability to be compressed Remembered this? Solids Liquids Gases Shape fixed shape no fixed shape Volume fixed volume no fixed volume Ability to be compressed incompressible compressible Kinetic Model of Matter can be used to explain the properties for each state of matter

Kinetic Model of Matter (Kinetic Particle Theory)

Video: Things to look out for Arrangement of particles Motion of particles Attractive forces between particles Speed of particles (if any)

Particles in a Solid Arrangement Closely packed together in a fixed, regular pattern, occupying minimum space. This results in solids having high densities

Particles in a Solid Movement Cannot move freely but vibrate about fixed positions. Held in position by very strong attractive forces This explains why solids have fixed volumes and shapes

Particles in a Liquid Arrangement Randomly arranged with the particles slightly further apart as compared to that of solids. This results in liquids having relatively high densities

Particles in a Liquid Movement Particles slide past one another Free to move about but confined within the vessel containing it. Have attractive forces between particles. This explains why liquids have fixed volume but will take the shape of vessels containing them.

Particles in a Gas Arrangement Very far apart. Particles are randomly arranged and will occupy any available space. This results in gases having relatively very low densities

Particles in a Gas Movement Particles have very little attraction between them and move about randomly at a very high speed.. This explains why gases have no fixed volume and shape, and why they are highly compressible.

The states of matter The relative strength of the intermolecular forces between the particles differ between the different states of matter

The states of matter The relative distances between the particles also differ between the different states of matter

A Summary… Matter is anything that has mass and occupies space All matter can exist in 3 physical states, Solid Liquid Gas depending on the temperature and pressure of their surroundings

Takes the volume of its container Solid Liquid Gas Volume Fixed Takes the volume of its container Shape Takes the shape of the part of the container it fills Takes the shape of the container Density High Medium Low Expansion on heating Little Moderate Large Ease of compression Difficult Easy

Kinetic Particle Theory A Summary… So why do solids, liquids and gases have such different properties? Kinetic Particle Theory

Kinetic Particle Theory All matter is made up of a large amount of tiny particles (cannot be seen by the naked eye) which are always in constant random motion Energy due to movement = Kinetic energy

Evidence of Kinetic Particle Theory? Diffusion – particles moving randomly from a region of high concentration to lower concentration in gases in liquids in solids???

Thinking Question: Now that you know the arrangement /movement of particles in solids, liquids and gases, can you compare the rates of particle movement (diffusion) in solids, liquids and gases and explain why it is so?

Thinking Question: If a solid is usually more dense than a liquid, why does ice float on water?

Role play 

Melting When a solid is heated, the particles absorb heat energy. The particles gain kinetic energy and start to vibrate faster and move further apart . At a certain temperature known as the melting point, the particles have enough kinetic energy to overcome the strong forces of attraction holding the particles together in the solid. The particles start to break away from one another and the solid becomes a liquid. At the liquid state, the particles start to roll and slide over one another

Freezing When a liquid is cooled, the particles release heat energy. The particles lose kinetic energy and vibrate slower. At a certain temperature known as the freezing point, the particles no longer have enough kinetic energy to overcome the strong forces of attraction holding them together. The particles start to come together in a regular arrangement and the liquid becomes a solid.

Boiling Particles in a liquid are held by strong attractive forces. When a liquid is heated, the particles absorb heat energy. The particles gain kinetic energy and slide over each other more rapidly. Eventually, the particles gain sufficient energy to overcome the attractive forces between the particles and move far apart rapidly in all directions.

Summary of today’s lesson All matter is made up of a large amount of particles in constant random motion The particles in a solid, liquid and gas are arranged differently – so they have different properties During change of state, the particles gain or lose energy, resulting in a change in the arrangement of the particles

Thinking question A liquid expands and changes into gas during boiling. Does it mean that the particles in a liquid become bigger and change their shape? The liquid expands because the particles move farther apart, so the space between them is bigger. The particle remain the same in size and shape.