Exploring the Nature of Matter

Particle Theory of Matter ► All matter is made up of extremely tiny particles. ► Each pure substance has its own kind of particle, different from the particles of other pure substances. ► Particles attract each other. ► Particles are always moving. ► Particles at a higher temperature move faster on average than particles at a lower temperature.

Scientific Models ► Scientific models help scientists to picture processes in nature that are difficult to directly see. ► The Particle Theory of Matter is an example of scientific model ► The first two points of the PTM allow us to understand how particles make up substances. ► The last three points explain properties like how particles stay together and how they behave when temperature changes.

States of Matter and the PTM ► Solids – particles do not have enough energy to move from place to place ► Liquids – particles have enough energy to break some of the attractive forces but not all of them. ► Gases – particles have enough energy to break all of the attractive forces

Change of State ► Solid to liquid (melting) – particles gain energy ► Liquid to gas (evaporation) – particles gain energy ► Gas to liquid (condensation) – particles lose energy ► Liquid to solid (solidification) – particles lose energy ► Gas to solid (deposition) – no liquid phase ► Solid to gas (sublimation) – no liquid phase

Classifying Matter ► Matter can be classified by its state (solid, liquid, or gas) ► Matter can also be classified according to one of its properties (heterogeneous or homogeneous substance) ► Heterogeneous – does not have a uniform composition (salad dressing) ► Homogeneous – consists of a uniform composition (salt, water, salt water, gold, etc.)

Classifying Matter ► Matter can also be classified based on its composition: a mixture or a pure substance ► Mixture – a substance composed of two or more particles ► Pure substance – a substance composed of one unique particle

Chemical and Physical Changes ► A chemical change occurs when:  a change in which something new is formed.  The starting materials change into an entirely different substance or substances. This new substance has a different chemical composition than the starting materials. ► Examples of chemical changes would be the reaction of iron with air (rusting} or the reaction of a metal and acid.

► Certain observations will indicate that a chemical change has occurred. These are:  The reaction produced a change in temperature.  Formation of gas bubbles.  Formation of a solid (precipitate).  A change in color.  Formation of a different odour.  Starting material is used up.  A material with new properties is formed. ► If two or more of the above occur then a chemical change has probably taken place.

► Physical change is a change in which the substance changes form but keeps its same chemical composition. ► Examples: ► Changes of state are considered to be physical changes. Liquid water and ice (frozen water) are both the same substance, water. ► If you fold a piece of paper it is a physical change. You have changed the form of the paper but you have not changed the fact that it is paper.

► If you heat an iron bar until it glows red hot, it is still chemically the same iron. The iron has not changed into something else. ► If you dissolve salt in water you have not changed the materials chemically. You still have salt and you still have water. This can be shown if you choose to separate the mixture by distillation or the simple evaporation of the water. The salt would be the residue and the water would be the distillate.

Physical Properties ► Physical properties are those that can be observed without changing the identity of the substance. The general properties of matter such as color, density, hardness, are examples of physical properties. ► Can you think of any physical properties?

Physical Properties ► Colour ► Taste ► Smell ► State of matter ► Malleability ► Ductility ► Melting point ► Boiling point ► Density ► Solubility ► Viscosity

Physical Properties ► The previous list can be broken into two types of physical properties: qualitative and quantitative. ► Qualitative Physical Properties: a characteristic that can be described but not measured. ► Quantitative Physical Properties: a characteristic that can be measured numerically.

Chemical Properties ► A characteristic of a substance that describes its ability to react chemically with another substance. ► Can you think of any chemical properties?  Combustibility  Reacts with air  Reacts with water  Reacts with oxygen  Reacts with….