Ch. 2 Learning Objectives1. I can classify pure substances. This means that I
know the difference between an element and a compound.
2. I can describe the characteristics of an element. This means that I know how elements are identified by using chemical symbols.
3. I can describe the characteristics of a compound. The means that I know the difference between a compound and other pure substances.
4. I can distinguish a pure substance from a mixture. This means that I know what makes them different.
Learning Objectives Continued5. I can classify mixtures. This means that I know what a
homogeneous and heterogeneous mixture is. I also know what a solution, suspension, and colloid is.
6. I can describe the physical properties of matter. This means that I know what each property is and how we can identify them.
7. I can describe how to separate a mixture. This means I can differentiate between filtration and distillation.
8. I can describe the chemical properties of matter. This means I can list the different properties.
9. I can describe how to tell that a change has a occurred. This means I can state the three ways to tell a change has happened.
Pure Substances Matter that always has exactly the same composition is
classified as a pure substance.
Examples: salt and sugar
**Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.
Substances are classified into two categories: elements and compounds.
Elements An element is 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 1 type of atom.
No two elements contain the same type of atom.
Examples of Elements
Solid elements at room temperature
Aluminum
carbon
Gas elements at room temperature
Oxygen
Nitrogen
Liquid elements at room temperature
Bromine
Mercury
Symbols for Elements Jons Berzelius, a Swedish chemist, suggested that
chemists use symbols to represent elements.
Characteristics of symbols:
1 or 2 letters (First letter is always capitalized)
Still used on the periodic table today.
Why is using symbols important?
So there is a universal symbol for all languages.
Compounds Water is composed of the elements hydrogen and
oxygen
Compounds
Are made from two or more simpler substances that can be broken down into those simpler substances.
Always contain 2 or more elements joined in a fixed proportion.
Mixtures **Properties can vary because the composition of a
mixture is not fixed. (this means the composition can change)
Mixtures In a heterogeneous mixture, the parts of the mixture
can be classified and noticeably different from one another.
Mixtures continued In a homogeneous mixture, substances are so evenly
distributed that it is difficult to distinguish one substance from another in the mixture.
Appears to be only one substance.
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
Solutions When substances dissolve and form a homogeneous
mixture, the mixture that forms is called a solution. Example: sugar and water
Liquid Solutions
Do not separate
Can not be filtered
Clear
**The particles in a solution are too small to settle out of the solution, be trapped by a filter, or scatter light
Suspensions Is a heterogeneous mixture that separates into layers
over time.
Example: sand and water
Can a suspension be filtered?
Colloids A colloid contains some particles that are intermediate
in between small particles in a solution and the larger particles in a suspension.
Do not separate into layers
Can not be filtered
Examples: Fog
Physical Properties A physical property is any characteristic of a material
that can be observed or measured without changing the composition of substances in a material.
Examples of Physical Properties Viscosity
Conductivity
Malleability
Hardness
Melting point
Boiling point
Density
Viscosity The resistance to flow
The greater the viscosity the slower the liquid moves
High viscosity liquids: honey, corn syrup
Low viscosity liquids: vinegar , water
Viscosity will decrease when the liquid is heated.
Conductivity Ability to allow heat to flow
Materials with high conductivity are called conductors.
Example: Metals
Other Properties Malleability – the ability of a solid to be hammered
without shattering.
Hardness – diamond is the hardest know material
Density – is used to test purity of a substance
Melting and Boiling Points
When a material has reached its melting point the material changes from a solid to a liquid
Using Physical Properties How are physical properties used:
To identify a material
To choose a material for a specific purpose
To separate substances into a mixture
Using Properties to Identify Materials What are the three steps used to identify a material?
Decide which properties to test
Test on the unknown sample
Compare results with data for known materials
Why is identifying a material important?
To solve crimes
Using Properties to Separate Mixtures What are the two separation methods?
Filtration- the process that separates materials based on the size of the particles.
Distillation- process that separates the substances in a solution based on their boiling points.
Example: providing fresh water
Recognizing Physical Changes When does a physical change occur?
When some of the properties of a material change, but the substances in the material stay the same.
Two examples: ice melting and hair styles
Observing Chemical Properties What is a chemical property?
Any ability to produce a change in the composition of matter.
When can a chemical property be observed?
Only when the substances in a sample of matter are changing into different substances.
What are the two examples of chemical properties?
Flammability – material’s ability to burn in the presence of oxygen
Reactivity – how readily a substance combines chemically with other substances.
Oxygen is a highly reactive element and nitrogen has an extremely low reactivity.
Recognizing Chemical Changes When does a chemical change occur?
When a substance reacts and forms one or more new substances.
Examples of a chemical change
Baking a cake
Ripening bananas
Leaves on a tree changing color
Key PointWhen matter undergoes a chemical
change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter stays the same.
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