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Pearson Prentice Hall Physical Science: Concepts in Action

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1 Pearson Prentice Hall Physical Science: Concepts in Action
Chapter 2 Properties of Matter

2 2.1 Classifying Matter Objectives:
1. Explain why elements and compounds are classified as pure substances 2. Distinguish mixtures and pure substances 3. Analyze the main difference among solutions, suspensions & colloids

3 Definition: a pure substance is matter that always has exactly the same composition
Any particular pure substance always has the same properties because the substance has a fixed, uniform composition Definition: an element is a substance that cannot be broken down in simpler substances

4 Elements as pure substances
Elements contain only one type of atom Elements have a fixed composition (due to only one type of atom) Examples of elements: gold (Au), silver (Ag) and platinum (Pt) Names of elements have one or two letters If there is a second letter, it is not capitalized

5 Compounds as pure substances
Definition: a compound is a substance that is made from 2 or more simpler substances, AND can be broken down into simpler substances A compound always contains 2 or more elements joined in a fixed proportion Since compounds are matter that always contain the exact same elements in the exact same proportions, they are pure substances

6 Mixtures are not pure substances
Recall that a pure substance is matter that always has exactly the same composition Mixtures vary in composition so they are not pure The properties of a mixture can vary because the composition of the mixture is not fixed Example: salsa- one batch may have more onions, fewer tomatoes or tons of peppers compared to another batch

7 Different types of mixtures
Definition: a heterogeneous mixture is not the same throughout Example: fruit salad Definition: a homogeneous mixture is the same throughout Example: rubbing alcohol or milk Mixtures are also classified by the size of the largest particles as solutions, suspensions or colloids

8 Solutions, Suspensions & Colloids
Definition: a solution is substances that dissolve into each other to form a homogeneous solution (& do not separate into layers) Definition: a suspension is a heterogeneous mixture that separates into layers over time such as sand & water Definition: colloids are heterogeneous mixtures that are made of very tiny particles & some intermediate sized particles of pure substances disbursed in another substance that do not settle out or separate such as gelatin

9 Examples of physical properties
Definition: a physical property is any characteristic of a material that can be observed or measured without changing the composition of the material Here are some examples: Viscosity- resistance of a liquid to flowing Conductivity- ability of material to allow heat to flow

10 Malleability- ability of a solid to be hammered without shattering
Hardness- resistance to scratching Melting point- the temperature at which a substance changes form solid to liquid Boiling point- the temperature at which a substance boils Density- the ratio of mass to volume or m/v

11 2.2 Physical Properties Objectives:
1. Give examples of physical properties 2. Explain the usefulness of knowing physical properties 3. Describe how mixtures are separated 4. Evaluate when a physical change has occurred

12 Usefulness of Physical Properties
Physical properties are used to identify a material, to choose a material for a specific purpose or to separate substances from a mixture The methods often involve math since many physical properties are described by numbers (boiling point and melting point, for example)

13 Separating Mixtures There are several ways Here are some examples:
Filtration- separating substances based on the size of the particles (sand from water, for example) Distillation- separation of substances based on their boiling points (requires that the boiling points are different from each other)

14 Magnetism- using magnetic property of some metals to separate from nonmagnetic materials
Density- some substances may float (less dense) in water, while others sink: using density this way allows separation of less dense substances from more dense substances such as driftwood floating on water

15 Recognizing Physical Changes
Definition: a physical change is a change in the physical form or properties of a substance that occurs without a change in composition The substances in the material remain the same Size and shape might change but not composition

16 Words that describe physical change
Examples of physical change include cutting, grinding, bending, water changing to steam, melting of ice Some words that describe physical change: boil, freeze, dissolve, melt, condense, break, split, crack, crush and dissolve

17 2.3 Chemical Properties Objectives:
1. Discuss when chemical properties can be observed 2. Summarize which observations might indicate a chemical change has occurred 3. Judge the difference between a chemical and physical change

18 Physical or Chemical? When matter undergoes a chemical change, the composition of the matter changes When matter undergoes a physical change, the composition of the matter remains the same

19 Observing Chemical Properties
Definition: a chemical property is the ability to produce a change in the composition of matter Chemical properties can be observed only when substances in a sample of matter are changing into different substances

20 Two types of chemical properties include flammability and reactivity
Definition: flammability is a material’s ability to burn in the presence of oxygen Definition: reactivity is the ability of a substance to combine chemically with other substances

21 Observations of chemical change
Change in color, production of gas, formation of precipitate Definition: a precipitate is any solid that forms when 2 liquids are mixed Other examples of chemical change: Burn, rot, rust, decompose, ferment, explode and corrode

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