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Introduction to Chemistry &

Classifying Matter (Section 2.1)

Matter

• Anything that has mass and takes up space

• Comes in many different forms

Mass • A measurement reflecting

the amount of matter • Mass and weight are not the

same o Weight measures the

earth’s gravitational pull on

matter

Chemistry at Different Levels

• Macroscopic (very large) to Sub-Microscopic level (very small)

•  Chemistry explains how changes at the sub-microscopic level lead to changes at the macroscopic level

Stuff

Matter

Elements

Particles

Atoms

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Classifying Matter

•  Based on their compositions, materials can be divided into pure substances and mixtures

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Pure Substances •  Matter that always has exactly the same

composition •  Every sample of a given substance has the

same properties because a fixed, uniform composition

•  Substances can be classified into two categories o Elements o Compounds

Elements •  A substance that cannot be broken down into

smaller, simpler substances •  An atom is the smallest particle of an element •  An element has a fixed composition because it

contains only one type of atom o  No two different elements contain the same type of atom

•  91 naturally occurring elements, plus others developed in the lab

•  Each element has a unique name and symbol

•  Are not equally abundant

Symbols for Elements •  Symbols for elements are either

one or two letters •  The first letter is always

capitalized and the second letter is not

•  Symbols allow scientists from different countries to communicate without confusion

•  Examples: o  Aluminum = Al o  Hydrogen = H o  Calcium = Ca o  Silver = Ag

Compounds •  Is a substance that is made from two

or more simpler substances and can be broken down into those simpler substances

•  A compound always contains two or more elements joined in a fixed proportion

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Mixtures •  A combination of two or more

pure substances, in which each pure substance retains its individual properties

•  Heterogeneous Mixtures o Does not blend smoothly o Individual substances remain

distinct •  Homogeneous Mixtures o Constant composition

throughout

Solutions, Suspensions, &

Colloids •  The size of the particles in a mixture have

an effect on the properties of the mixture •  Based on the size of its largest particles, a

mixture can be classified as a solution, a suspension, or a colloid

Solutions •  Formed 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 o They do not separate into distinct layers o None of the substances get trapped when

passed through a filter o Light can pass through without being scattered in all directions

Suspensions •  Is a heterogeneous mixture that

separates into layers over time •  Suspended particles settle out

of a mixture or are trapped by a filter (larger particles than that in the solution)

•  Suspensions are cloudy because the larger particles can scatter light in all directions

Colloids

•  Contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension

•  Does not separate into layers •  Cannot use a filter to separate parts •  Light is scattered when going through a colloid o The scattering of light is a property that can

be used to distinguish colloids and suspensions from solutions

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