2.1 Classifying Matter
Pure Substances
matter that always has exactly the same composition(also called simply substance)
- ex. table salt/sugar
KEY: Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.
Summary statement: key
Elements
Atom:smallest particle of an element
- Ex. Cutting copper wire into small pieces, eventually end up with extremely tiny copper atoms.
KEY: An element has a fixed composition because it contains only one type of atom
Element: A substance that cannot be broken down into simpler substances. - Ex. only about 100
- no 2 elements contain same type of atom
Summary statement: key
Examples of Elements
At room temp. elements are:
Most are solids
- Ex. aluminum, carbon
Some are gases
Only 2 liquids
- Bromine and mercury
- Both extremely poisonous
Summary statement: Elements come in different forms at room temperature, but most are solid.
Symbols for Elements
1813, Jons Berzelius suggested chemists use symbols to represent elements
Each symbol either has one or two letters
First letter always capitalized
Based on latin name of elements
Allow scientists who speak different languages to communicate
Summary Statement: Says element names and how they are set up
Sometimes name contains clue to its properties
Compound
click to edit
KEY: A compound always contains two or more elements joined in a fixed proportion.
Summary Statement: key
Definition: Substance that is made from two or more simpler substances and can be broken down into those simpler substances. Simpler substances either elements or other compounds.
Mixture:
Tend to retain some of the properties of their individual substances.
Can be classified by how well the parts of the mixture are distributed throughout the mixture.
KEY: The properties of a mixture can vary because the composition of a mixture is not filed.
Summary Statement: key
Heterogeneous Mixtures:
Define: parts of the mixture are noticeably different from one another
Ex. sand
Summary Statement: parts of mixture noticeably different
Homogeneous Mixture:
Define: substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another.
Ex. water from deep end and shallow end of pool
Appears to contain only one substance
Summary Statement: looks like it only has one substance
Solutions, suspensions, colloids:
KEY: Based on the size of it's largest particles, a mixture can be classified as a solution, suspension, or colloids.
Summary statement: key
Solutions:
Define: When substances dissolve and form a homogeneous mixture, that mixture that forms is the solution.
- Ex. spoonful of sugar in hot water
Liquid solutions:
Easy to recognize
Do not separate into distinct layers over time
Suspensions:
Define: is a heterogeneous mixture that separates into layers over time.
- Ex. if you shake up a container of sand and water , the sand mixes with the water and forms a suspension. Overtime, suspended particles of sand settle to the bottom of the container.
Colloids:
Define:Colloids: contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension.
- Ex. milk processed and not processed(cream), fog of water droplets in air
Do not separate into layers