Properties of Matter

Chapter 2

Physical Science CIA

Classifying Matter

Section 2.1

Pure Substances

• Matter that always has exactly the same composition is called a pure substance.

• Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.

• Substances can be either:

Elements OR

Compounds

Elements

• Millions of substances…only ~ 100 elements.

• Elements cannot be broken down into simpler substances

• An atom is the smallest particle of an element.

• Elements contain only one type of atom.

Elements, ctd.

• At room temp (20oC), most elements are solids. (Ex. aluminum, copper, carbon…)

• Some are gases at room temp. (Ex. oxygen, nitrogen…)

• Only 2 are liquids at room temp. (Bromine & Mercury)

Elements, ctd.

• We use symbols to represent elements

• Symbols have either one or two letters, the first is capitalized, the second (if present) is not.

• What are the advantages of using symbols?

Compounds

• A compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances.

• The simpler substances are either other compounds or elements.

Compounds, ctd.

• The properties of a compound differ from those of the substances from which it is made.

• A compound always contains 2+ elements joined in a fixed proportion.– Ex: H2O, SiO2, CO, CO2

Mixtures

• Mixtures tend to retain some of the properties of their individual substances

• The properties of a mixture aren’t always as constant as those of a pure substance.

• The properties of a mixture can vary because the composition of a mixture is not fixed.

Mixtures, ctd.

• Mixtures are classified by how well the parts of the mixture are distributed throughout.

1. Heterogeneous: parts of the mixture are noticeably different from one another (ex. sand, salsa,…)

2. Homogeneous: substances are evenly distributed; tough to distinguish one from the other (ex. steel, tap water…)

Solutions, Suspensions, Colloids

• Mixtures can also be classified by the size of its largest particles

• These classifications are:1. Solutions

2. Suspensions

3. Colloids

Solutions

• Solution: when substances dissolve and form a homogeneous mixture

– Do not separate into layers over time

– Cannot be filtered

– Light can pass through easily

– Particles are SMALL!

Suspensions

• Suspension: A heterogeneous mixture that separates into layers over time

– Can be filtered– Particles do settle out– Scatters light (appears cloudy)– Particles are BIG! (relatively speaking)

Colloids

• Colloids: contain some particles that are in the middle of the small particles of solutions and the big particles of suspensions.

– Do not separate into layers– Can’t be filtered– Do scatter light

Physical Properties

Section 2.2

Physical Properties

• Physical Property: A characteristic of a material that can be observed or measured without changing the composition of the substances in the material.

Physical Properties, ctd.

• Phys. Properties can be used to:

–Identify materials (ex. CSI)

–Choose materials (ex. nylon shoelaces, gold in teeth, steel for cars…)

Interest GrabberDistinguishing FeaturesPhysical characteristics can be used to describe and distinguish a person from other people. An accurate physical description can often be used to identify a person in a crowd. Practice identifying physical characteristics with the animals listed below. Your teacher will supply you with pictures of each animal.

lion cheetahocelot leopardtiger bobcat

1. What characteristics make these animals similar?

2. What characteristics make them different?

Section 2.2

Lion ocelot cheetah

Tiger leopardbobcat

Physical Properties Examples

• Viscosity• Conductivity • Malleability• Hardness

• Melting point • Boiling point

• Density

Viscosity

Physical Properties

• Viscosity is the resistance to flowing. The greater the viscosity, the slower the liquid moves.– Heating the liquid decreases the viscosity.– Corn syrup and honey have a high viscosity.

Conductivity

Physical Properties

• Conductivity is the ability to allow heat or an electric current to flow.– Materials with a high conductivity include

metals.– Wood is a poor conductor.

Malleability

Physical Properties

• Malleability is the ability of a material to be hammered into thin sheets.– Gold is used in jewelry because of its

malleability.– Glass is not malleable and will shatter when

hammered because it is brittle.

Hardness

Physical Properties

• Hardness is one way to compare 2 materials, to see which one scratches the other.

Density

Physical Properties

• Density is the amount of matter (mass) in a specific space (volume)– Most substances are then compared to pure

water which has a density of 1g/cm3 or 1g/mL

Physical Changes

• Physical Change: some of the properties of a material change, but the substances in the material remain the same

• Examples:– Melting or boiling

– Crumpling or slicing

– SOME physical changes can be reversed

Physical Properties

• Melting and boiling points are specific to different substances.– The melting point is the temperature at which

a solid changes into a liquid.– The boiling point is the temperature at which a

liquid changes into a gas.

Melting and Boiling Points of Some Substances

Figure 12

Reading StrategyBuilding Vocabulary

Section 2.2

a. The tendency of a liquid to resist flowing b. The ability of a solid to be hammered without shattering c. The temperature at which a substance changes from a solid to liquid.

Chemical Properties

Section 2.3

Chemical Properties

• Chemical Property: the 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.

Chemical Properties

Examples

• Flammability – ability to burn in presence of O2

• Reactivity – how readily a substance combines chemically with other substances. NaCl video

Chemical Changes

• Chemical Change: occurs when a substance reacts and forms one or more new substances

• Evidence for chemical changes:– Color change– Production of gas– Formation of precipitate (= a solid that forms

and separates from a liquid mixture)

Chemical or Physical Change?

• If the composition of the matter changes, it is a chemical change.

• If the composition of the matter remains the same, it is a physical change.