Chapter 2 Properties of Matter

2.1 Classifying Matter

Pure Substances• Pure Substances: matter that always has

exactly the same composition– Every sample has the same properties because a

pure substance has a fixed, uniform composition– Ex: table salt & gold

Pure Substances

• There are 2 categories of Pure Substances:1. Elements

2. Compounds

Elements

• Element: a substance that cannot be broken down into simpler substances

• Elements contain only one type of atom– Ex: Copper wire is made up of only copper

atoms– More examples: carbon, gold, aluminum,

iodine (see the Periodic Table)

Elements

• Elements are represented with symbols– Ex: C = carbon, I = iodine, Au = gold

– Au ????? Well the Latin name for gold is aurum

Compounds

• Compound: a substance that is made up from 2 or more atoms chemically bonded together– A compound can be broken down, but only by

chemical means– Ex: NaCl = Sodium chloride or table salt

Elements

• The properties of the elements that make up a compound are different than the compound that they form– Ex: H2O water

– What are the properties of H & O when they are not bonded together?

Question

• Question: Can water have any other proportion than 2 hydrogen and 1 oxygen?– Can H3O be water?

Answer

• Of course not!! That’s because the elements that make up a compound are joined in a fixed proportion!

Mixtures

Now to the other side of the Map…

Mixtures• Mixture: contains parts that are combined

but the parts can be put together in varying amounts (it is NOT a fixed proportion)

• And…

• The parts retain their individual properties– Ex: Salsa

Types of Mixtures

• There are 2 kinds of mixtures:1. Heterogeneous

2. Homogeneous

• Mixtures are classified by how well mixed they are

Heterogeneous Mixtures• Heterogeneous Mixture: has parts that are

noticeably different from one another– Ex: Salsa and beach sand– Ex: Suspensions such a sand and water mixed

together• It will separate into layers over time• A filter could be used to separate because of larger

particles (Filtration)

Homogeneous Mixtures

• Homogeneous Mixture: is so well mixed that it is difficult to distinguish the parts

• In other words, it looks like a pure substance or like it is all the same stuff– Ex: a salt water mixture

Homogeneous Mixtures • Types of Homogeneous mixtures

– Solutions: substances dissolved together (smallest sized particles)

• Ex: sugar water, salt water, pool water

– Colloids: intermediate sized particles that are suspended between small sized particles that do not separate

• Ex: milk & fog

2.2 Physical Properties

Physical Property

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

Examples of Physical Properties

• Our textbook describes 6 physical properties, however there are many more!1. Viscosity

2. Conductivity

3. Malleability

4. Melting Point

5. Boiling Point

6. Density

Viscosity

• Viscosity: tendency of a liquid to keep from flowing – it’s resistance to flowing– The slower a substance moves, the higher its

viscosity– Viscosity decreases when it is heated– Example: Which has the higher viscosity: water

or honey?

Conductivity

• Conductivity: material’s ability to allow heat/electricity to flow– Which spoon should you choose for stirring a

pot of soup heating on the stove – a metal spoon or a wooden spoon? Why?

Conductivity• Conductors have HIGH conductivity

– Examples?

• Insulators have LOW conductivity– Examples?

• Which items are conductors? Insulators?

Malleability

• Malleability: ability of a solid to be hammered without shattering– What types of solids would be considered

malleable?

– What types of solids are brittle (the opposite of malleable)?

Hardness

• One way to compare the hardness of two materials is to see which of the materials can scratch the other.– Compare the hardness of various materials

Mohs Hardness Scale

Melting & Boiling Points

• Melting Point: temperature which a substance changes from a solid to liquid– For water, this occurs at what temperature in

Celsius?

• Boiling Point: temperature which a substance boils (liquid to a gas)– For water, this occurs at what temperature in

Celsius?

Density• Density is the ratio of the mass of a

substance to its volume.– Calculated by dividing the mass by the volume

• Density = Mass / Volume

• Used to test the purity of a substance

Using Physical Properties

• Physical properties can help us do the following:– Identify unknown materials– Choose appropriate materials

• Would you ever make shoelaces out of wood??!!

Separating Mixtures

• Some properties can be used to separate mixtures:– Filtration– Distillation

Filtration

• Filtration: physical process that separates materials based on the size of their particles– Examples: making coffee & tea, separating

sand from water

Distillation

• How can you separate the parts of a solution when all particles are small enough to pass through a filter?

• Distillation: physical process that separates the substances in a solution based on their boiling points.– Example: distillation of sea water to create

fresh water

Distillation

Physical Changes

• Physical Change: when some of the properties of a material change, but the substances in the material remain the same– Examples: braiding hair, cutting paper, melting

butter, boiling water

Reversible Physical Changes

• Some physical changes can be reversed.– Examples reversible physical changes:

– Examples of non-reversible physical changes:

2.3 Chemical Properties

Observing Chemical Properties

• Chemical properties can be observed only when the substances in a sample of matter are changing into different substances!

• Two examples include:– Flammability– Reactivity

Flammability

• Flammability: a material’s ability to burn in the presence of oxygen– Examples of flammable objects: paper &

gasoline

Reactivity

• Reactivity: how readily a substance combines chemically with other substances– Example: Rust – reaction that occurs when

oxygen reacts with iron and water

Reactivity

• QUESTION: Nitrogen & oxygen are the two most abundant gases in the atmosphere. Is it possible that both gases are highly reactive? Explain your answer…

Chemical Changes

• Chemical Change: occurs when a substance reacts and forms one or more NEW substances– Examples: baking a cake, leaves changing

colors in the fall, & food digested in your stomach

Recognizing a Chemical Change

• There are 3 common clues that a chemical change has taken place:– Change in color– Production of a gas– Formation of a precipitate

Change in Color

• EXAMPLES:– Over time a shiny silver bracelet that is exposed

to air will darken– As a match burns, it shrivels up and turns black– A new copper roof will turn green with time

• All of these are clues that a chemical change has occurred

Production of a Gas

• EXAMPLES:– Mixing vinegar and baking soda bubbles of

carbon dioxide (CO2)

– Baking power used when baking as the cake bakes, bubbles of CO2 expand and cause the cake to rise

Click HERE for video

Formation of a Precipitate

• Precipitate: any solid that forms and separates from a liquid mixture– If you add lemon juice or vinegar to milk, small

bits of white solid will separate from the liquid– When acid is added to milk, proteins in the

milk undergo a chemical change that alters their structure, causing them to stick together in clumps

Precipitates

Be CAREFUL With the Chemical Change Clues!!!

• Do the coils on a hot stove top mean a chemical change has occurred?

• When water boils on a stove, what are the bubbles that rise to the surface?

Chemical or Physical

• Before you decide if it was a chemical or physical change – ask yourself this question:– Are different substances present after the

change takes place…if not, then the change is physical, not chemical.

• When matter undergoes a chemical change, the composition of the matter changes! When matter undergoes a physical change, the composition of the matter remains the same!

Chemical Change Video Review