 Chemistry: the branch of science concerned with the organization of matter and explaining why it behaves as it does  All kinds of matter have properties to describe its appearance and behaviour

 Physical properties are those that can be observed/measured  Examples: Color (blue, green) State(solid, liquid, gas) Odour(foul, sweet) Melting point(0ºC) Density(1 g/mL)

 Chemical properties are those which describe how a substance behaves when it is reacting with something to form a new substance Example: hydrogen is very flammable when reacted with oxygen

 Chemical properties: Combustibility (burns easily in oxygen) Reactivity (highly reactive with water, or does not react) Toxicity (highly toxic gas, non-toxic solid)

 Changes that matter undergoes can be divided into two categories:  Physical changes alter the appearance or form of a substance, without producing a new substance Changes of state (ie. Ice melting) or changes of form (ie. Shredding paper)

 Chemical changes result in the production of a totally new substance Example: breaking down water into hydrogen and oxygen gases, or burning paper

 Chemical changes occur when a new substance appears, with new properties.  The following are clues that a chemical change may have taken place: Heat is produced or absorbed A new color appears A gas is produced (may be seen as bubbles in a liquid) A solid called a precipitate forms when two liquids are mixed A new odor is produced

 There are mixtures and pure substances  Mixtures are composed of two or more substances that are physically combined They have a variable composition They can be separated by physical means  Example: sand and water, salt water

 There are many types of mixtures, but for our class, we are going to learn about:  Suspensions: particles can be seen with the unaided eye and gravity will cause them to separate over time Example: oil and vinegar  Mechanical Mixture: particles stay mixed and can be seen with unaided eye Example: cereal, rocks, soil

 Solutions often involve one substance being dissolved in another Particles are so small that they are best seen with a microscope  Solvent: substance in which the solute dissolves (often a liquid, like water)  Solute: the substance that dissolves in the solvent (often a powder)

 Alloys: one solid dissolved in another (they must be heated first, of course)  Examples: steel (iron and carbon), and bronze (copper and tin)

 Pure substances are composed of one substance only they have a constant composition Cannot be separated by physical means  There are two types: Elements Compounds

 Elements: Cannot be broken down by physical or chemical means Composed of one type of atom Elements combine to form all matter Examples: gold, aluminum, carbon, oxygen

 Compound: Two or more elements bonded together chemically They cannot be broken down by physical means but can be broken down by chemical means Examples: water, copper sulfate