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?