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
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.)
Who is right? Democritus or Aristotle? Let’s vote! Let’s see who’s right…
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
Remembered this? Kinetic Model of Matter can be used to explain the properties for each state of matter
Video: Things to look out for • Arrangement of particles • Motion of particles • Attractive forces between particles • Speed of particles (if any)
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
A Summary… So why do solids, liquids and gases have such different properties? Kinetic Particle Theory
Kinetic Particle Theory Matter is made of tiny discrete particles(atoms or molecules), which are in constant and 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 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?
Matter Melting Boiling Gas Solid Liquid Freezing Condensation Deposition Sublimation
Change in State of Matter Temperature / °C gas liquid-gas boiling point boiling liquid solid-liquid melting point solid melting Time / s II III I IV V
Change in State of Matter Temperature / °C gas liquid-gas condensation point liquid condensation solid-liquid freezing point solid freezing Time / s II III I IV V
Melting When a solid is heated, the particles absorb thermal 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
Melting Temperature / °C boiling point melting point Time / s II III I IV V In other words, during phaseII (melting), thermal energy supplied is used to do work to overcome the strong forces of attraction holding the particles together in the solid.
Freezing • When a solid is cooled, the particles release thermal 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 thermal 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 in a liquid and move far apart rapidly in all directions.
Summary of today’s lesson All matter is made up of a tiny discrete particlesin 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.