Pearson Prentice Hall Physical Science: Concepts in Action

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

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

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

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 • http://www.chemicool.com/

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

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

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

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

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

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

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

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)

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)

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

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

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

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

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

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

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

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

Pearson Prentice Hall Physical Science: Concepts in Action