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