Chapter 2 Notes
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Ch. 2 Learning Objectives
1. 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 Continued
5.
6.
7.
8.
9.
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.
I can describe the physical properties of matter. This
means that I know what each property is and how we can
identify them.
I can describe how to separate a mixture. This means
I can differentiate between filtration and distillation.
I can describe the chemical properties of matter.
This means I can list the different properties.
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.
Section 2.1:
Classifying Matter
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
Evidence of a chemical change
Change in color
Production of gas
Formation of precipitate
Ask yourself…
Are different substances
present after the change takes
place?
Key Point
When 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.
Homework
Page 58
Section 2.3 Assessment
Questions # 4-8