Classifying Matter Ch. 2

Matter Pure Substance- matter that always has exactly the same composition. – Ex: every pinch of salt tastes equally as salty Substances can be classified into two groups: – Elements and Compounds

Elements Elements- a substance that cannot be broken down into simpler substances. – There are about 100 known elements – An Atom is the smallest particle of an element. – Each element contains only one atom! – Find these different elements on the periodic table.

Elements Examples of elements you may come into contact with everyday: – Aluminum – Carbon – Oxygen – Carbon dioxide – Nitrogen

Elements Elements on the periodic table are labeled with a symbol. – Symbols allow scientists who speak different languages to communicate with ease. – Symbols are based on the Latin name and first letter is always capital while second is lower case. Ex: Gold, Au = aurum Iron, Fe= ferric

Compounds Compound- two or more simpler substances put together. – Water= compound of hydrogen and oxygen Properties of a compound can differ from those substances which make it up. – Ex: Water is a liquid, but hydrogen and oxygen are gases

Mixtures Mixture- different substances mixed together – Tend to retain some of the properties of their individual substances Two types of mixtures – Heterogeneous mixtures- different, particles are noticeably different from one another – Homogeneous mixtures- same, particles are so evenly distributed its hard to distinguish one substance from another.

Solutions When substances dissolve and form a homogeneous mixture, the mixture that forms is called a solution. – Ex: dissolve sugar in water – Will not settle out – Can not be trapped by filter – Can not scatter light

Suspensions A heterogeneous mixture that separates into layers over time. – Ex: mix sand and water, let sit, and it will separate – Can use a filter to separate, – Will settle out, and – Can scatter light

Colloids Colloids contain particles that are intermediate in size. – Can not be filtered, and – Can not separate into layers, but – Can scatter light – Ex: fog

Physical Properties Any characteristic of material that can be observed or measured without changing the composition of the substances in the material. – Ex: Viscosity, conductivity, malleability, harness, melting point, boiling point, and density

Viscosity/ Hardness The tendency of a liquid to keep from flowing. – The greater the viscosity, the slower the liquid flows. Ex: honey and syrup – Viscosity tends to decrease as the liquid is heated Hardness is how hard a material is – Check by seeing if one material can scratch the other – Ex: diamond ring can scratch glass (it’s the hardest know material.)

Conductivity/ Malleability A material’s ability to allow heat to flow – High conductivity= metals (aka conductors) – Poor conductor= wood The ability of a solid to be hammered without shattering – Most metals are malleable.

Melting/ Boiling Point MP- temp at which a substance changes from solid to liquid. – Ex: Water changes normally at 0ᵒC BP- temp at which a substance boils. – Ex: water starts to boil at 100ᵒC

Density Can be used to test the purity of a substance – Ratio of the mass of a substance to the volume D= m/v – Ex: If silver has a density of 10.5 g/cm3, and you measure a coin to be 9.9 g/cm3, then the coin may not be made from silver or may have other substances added in.

Physical Properties Used to identify a material – Ex: Crime scene To choose a material for a specific purpose – Ex: what material to make shoelaces from To separate the substances in a mixture. – Ex: filtration and distillation

Filtration Separates materials based on the size of their particles. – Ex: coffee filter separates the brewed coffee from the coffee grounds.

Distillation Process that separates the substances in a solution based on their boiling points. – Ex: Boil salt water Water has a lower boiling point than compounds dissolved in seawater. Water is boiled until it turns into a gas, then the gas is cooled and collected in a different container

Recognizing Physical Change Occurs when some of the properties of the material change, but the substance in the material remain the same. – Changing states of matter – Slicing a tomato – Peeling an orange

Chemical Properties Any ability to produce a change in the composition of matter. Chemical properties can be observed only when the substances in a sample of matter are changing into different substances. Examples: – Flammability and reactivity

Flammability/ Reactivity Flammability is a material’s ability to burn in the presence of oxygen. Examples: – Burning candle, automobile gasoline, campfire Reactivity is the property that describes how readily a substance combines chemically with other substances. – Oxygen is a highly reactive element. – Nitrogen has an extremely low reactivity. Examples: – Rusty automobile

Recognizing Chemical Changes A chemical change occurs when a substance reacts and forms one or more new substances. The common types of evidence for a chemical change are: – change in color – the production of gas – formation of a precipitate Precipitate is any solid that forms and separates from a liquid mixture

Chemical Changes Examples: – ripening banana – leaves on trees changing color – vinegar and baking soda – a baking cake – food digested in your stomach – vinegar and milk

Chemical or Physical Change? Ask yourself: – Are different substances present after the change takes place? If no, then the change is physical. – When matter undergoes a physical change, the composition of the matter remains the same. If yes, then the change is chemical. – When matter undergoes a chemical change, the composition of the matter changes.

Which is it?