Chapter 2

2.1

 Pure Substances  Elements  Compounds  Mixtures  Solutions, Suspensions and Colloids

 Matter that always has exactly the same composition  Every sample of a substance has the same properties because a it has a fixed composition.  Ex: salt, sugar, flour  2 Types 1. Elements 2. Compounds

 Cannot be broken done into simpler substances  fixed composition because contains only one type of atom  No two elements contain the same type of atom  Atom = smallest particle of an element

Gold Aluminum Carbon Sodium

 Made from two or more simpler substances  Contains two or more elements in a fixed proportion  Can be broken down into its simpler substances (either elements or other compounds)  Properties of a compound differ from those substances from which it is made

 Sodium Chloride  Sodium: soft, highly reactive metal  Chlorine: greenish colored gas, can be toxic

 Liquid Petroleum Gas (mixture of propane and butane gas)  Made-up of carbon and hydrogen.  Both gases  More reactive than diesel, thus spark ignition

 Petrol Diesel (mixture of hydrocarbons)  Made up of carbon and hydrogen  Both Gases  Does not burn as easily as gasoline thus air is compressed in cylinder and creates higher temperatures

Pure Substances: same properties, uniform composition Elements: Fixed composition, contains one type of atom Compounds: two or more elements in a fixed proportion

 Properties of mixtures can vary because the composition is not fixed  2 Types: Heterogeneous and Homogeneous

 Parts of mixture are different from one another  Ex: salsa, salad, sand

 Substances are so evenly distributed it can hard to distinguish them  Ex: stainless steel, made of iron, chromium and nickel  Swimming pool, water at the shallow end is the same as the water at the deep end

 Size of particles in a mixture effect the properties  Based on the size of the largest particle a mixture can be classified as a solution, suspension or a colloid

 When substances dissolve and form a homogeneous mixture  Ex: tap water, lemonade  Can see light through these solutions  Particles are small so light passes through without being scattered in all directions  Particles will not settle out but can be filtered out

 Heterogeneous mixture that separates into layers over time  Suspensions are cloudy because larger particles can scatter light  Ex: Muddy water, sawdust in air

 Contains some particles that are intermediate (between solution and suspension)  Do not separate into layers  Cannot filter out particles  Scatters light  Ex: Fog, milk

2.2

 Characteristic that can be observed or measured without changing the composition (make-up) of a substance  Viscosity, conductivity, malleability, hardness, melting point, boiling point and density

 Resistance to flowing  Greater the viscosity the slower the liquid  Thin liquids have a low viscosity  Ex: Honey vs. soda  Heating up a liquid lowers its viscosity  Ex: oil

 Ability to let heat flow  Materials with high conductivity are called conductors  Ex: Metals

 Resistance to scratching  The hard the material the less likely it can be scratched and the more likely it will scratch something else  Ex: Diamond Drill Tips

 Melting Point: temperature a substance goes from a solid to a liquid  Boiling point: temperature at which a substance boils

 Amount of matter in an object  Ratio of the mass to volume  Different substances have different densities  D = M/V

 Used to identify materials  Choose materials for a specific purpose  Separate materials in a mixture  Filtration and Distillation

 Separates materials based on size of particles

 Separates substances based on their boiling points

 Occurs when some properties of the material change but not the composition  Some are reversible, some are not

2.3

 Chemical Property: ability to produce a change in the composition of matter  Observed only when substances are changing into different substances  Ex: Flammability and Reactivity

 Materials ability to burn in presence of oxygen

 How easily a substance combines chemically with another  Ex: Rust (oxygen and iron)  Ex: Water and baking soda

 Chemical Change: when a substance changes from one form to another  Evidence of Chemical changes: 1. Change in color 2. Production of gas 3. Formation of a precipitate (a solid that forms)