Chapter 2: Properties of Matter
(Matter: all of the stuff that makes up everything.)
· There are different types of changes in matter that happen.
2.1: Classifying Matter: anything that has mass and takes up space.
The Big Question: There’s a lot of different kinds of “stuff” in this great big world; how do we tell or describe what’s what?
I. Pure Substances: Matter that always has exactly the same composition, or simply a substance.
· Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.
· Substance can be classified into two categories: elements & compounds.
A: Elements: a substance that cannot be broken down into simpler substances.
· An atom is the smallest particle of an element.
· An element has a fixed composition because it contains only on type of atom.
B: Compounds: 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 elements or other compounds.
· A compound always contains 2 or more elements joined in a fixed proportion.
II. Mixtures: tend to retain some of the properties of their individual substances.
· The properties of a mixture can vary because the composition of a mixture is not fixed.
· There are 2 types of mixtures: heterogeneous & homogeneous
A: Heterogeneous Mixtures: the parts of the mixture are noticeably different from one another.
B: Homogeneous Mixtures: the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another.
Summary of the Types of MatterType of Matter / Definition (own words) / Examples
Homogeneous
Mixture
Heterogeneous
Mixture
Element
Compound
III. Solutions, Suspensions, and Colloids: based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid.
A: Solutions: when substances dissolve and form a homogeneous mixture.
· The particles in a solution are too small to settle out of the solution, be trapped by a filter, or scatter light.
B: Suspensions: is a heterogeneous mixture that separates into layers over time.
· Because the particles are larger they can scatter light, look cloudy, the particles settle out and can be filtered.
C. Colloids: contains some particles that are intermediate is size between the small particles in a solution and the larger particles in a suspension.
· The particles cannot be separated by a filter, they do not settle out or form layers and they scatter light.
Properties of solutions, suspensions, and colloidsApproximate size of solute particles / Solute particles
Settle / Can be separated by filtering / Particles scatter light
Solutions / 0.01 – 1.0 nm
Colloids / 1.0 – 1,000 nm
Suspensions / >1000 nm
2.2 Physical Properties
The Big Question: What observations will help us describe all of this stuff?
I. Examples of Physical Properties:
· A physical property is any characteristic of a material that can be observed or measured without changing the composition of the substances in the material.
· Those properties include size, shape, and state of the matter.
A: Viscosity: the tendency of a liquid to keep from flowing, its resistance to flowing.
· Thick liquids (corn syrup, honey) have a high viscosity.
· Thin liquids (water, vinegar) have a low viscosity.
· Colder temp = more viscous
· Warmer temp = less viscous
B: Conductivity: a material’s ability to allow heat to flow.
· If a material is a good conductor of heat, it is usually also a good conductor of electricity.
· Metals are good conductors of heat.
· Wood is not a good conductor of heat, it would be an insulator.
C: Malleability: is the ability of a solid to be hammered without shattering.
· Most metals are malleable.
· Ice cubes & glass are not malleable.
· Solids that shatter when struck are brittle.
D: Hardness: measures a solid’s resistance to scratching.
· Diamond is the hardest natural substance found on Earth.
E: Melting and Boiling Points:
· Melting Point: the temperature at which a substance changes from solid to liquid.
· Boiling Point: the temperature at which a substance boils.
F: Density: the ratio of the mass of a substance to its volume.
Using Physical Properties: they are used to identify a material, to choose a material for a specific purpose, or to separate the substances in a mixture,
Using Physical Properties to Separate Mixtures: 2 common methods are:
A. Filtration: a process that separates materials based on the size of their particles.
B. Distillation: a process that separates the substances in a solution based on their boiling points.
Recognizing Physical Changes: they occur when some of the properties of a material change, but the substances in the material remain the same.
2.3 Chemical Properties
The Big Question: Sometimes when you mix stuff together, stuff happens. What’s going on?
I. Observing Chemical Properties:
· A chemical property is 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.
· Flammability and reactivity are 2 examples of chemical properties.
A: Flammability: a material’s ability to burn in the presence of oxygen.
B: Reactivity: the property that describes how readily a substance combines chemically with other substances.
· The element oxygen is a highly reactive element.
· The element nitrogen has an extremely low reactivity.
II. Recognizing Chemical Changes
· A chemical change occurs when a substance reacts and forms one or more new substances. The breaking of bonds in one
or more substances, and the reforming of new bonds to create new substances.
· You know a chemical change has occurred when one or more starting substances are mixed and you get products (stuff) that appear to be different from those starting substances.
· Atoms are rearranged when chemical changes occur.
· You can use your powers of observation to determine that a chemical change has taken place.
· All chemical reactions involve the rearrangement of atoms
Some clues/evidence that a chemical change has occurred.
A: Change in Color: You mix some stuff together and the turns a completely different color (mix reactants, a reaction occurs and you get a product).
B: Production of a Gas: (Think of eating a lot of Bean Burritos!) You mix some stuff and bubbles, a gas appears (mix reactants, a reaction occurs and you get a product).
C: Formation of a Precipitate: You mix 2 liquids together and a solid forms and separates (mix reactants, a reaction occurs and you get a product).
· Precipitate: any solid that forms and separates from a liquid mixture
D: Temperature Change: You mix 2 or more things and they get hotter or colder (mix reactants, a reaction occur and you get a product).
E: Others:
III. So what is it: A Physical Change or a Chemical Change?
The Big Question: What’s the difference between a physical change and a chemical change in matter? There are different types of changes in matter that happen.
· You need to ask yourself: are different substances present after the change takes place?
o If YES: It’s a chemical change.
o If NO: It’s a physical change.
· Physical Change: When mater undergoes a physical change, the composition of the matter remains the same.
· Chemical Change: When matter undergoes a chemical change, the composition of the matter changes.
· You know a chemical change has occurred when one or more starting substances are mixed and you get products that appear to be different from those starting substances.
Vocabulary Terms You Need To KnowPure substance / Physical property / Chemical property
Element / Viscosity / Flammability
Atom / Conductivity / Reactivity
Compound / Malleability / Chemical change
Heterogeneous mixture / Melting point / Precipitate
Homogeneous mixture / Boiling point
Solution / Filtration
Suspension / Distillation
Colloid / Physical change