Chapter 22.1 Classifying Matter

Classifying Items• People classify objects for different reasons.

Classifying food into groups, such as grains, vegetables, and fruits help people plan meals that maintain a healthy diet. Biologists classify organisms into groups that have similar characteristics, which makes the relationships among organisms easier to see.▫Devise a classification system for the following items:

orange, lime, plum, apply, pear, rose, violet, daisy, gold, and silver.

▫Explain what criteria you used to place items into each category of your classification system. (Teacher Note: Try classifying by syllables)

2.1 Classifying Matter• Pure substances- Matter that always has exactly the same

composition. There is a fixed, uniform composition.• Substances can be classified into two categories:

▫ Elements A substance that cannot be broken down into simpler

substances. There are just over 100 elements.▫ Atom- The smallest particle of an element.

An element has a fixed composition because it contains only one type of atom.

• No two elements contain the same type of atom.

•Examples:

Pure Substances Con’t.• Compounds

▫ A substance that is made from two or more simpler substances and can be broken down into those simpler substances. The properties of a compound differ from those of the

substances from which it is made. A compound always contains two or more elements

joined in a fixed proportion.

Mixtures• Mixtures tend to retain some of the

properties of their individual substances. ▫ The properties of a mixture can

vary because the composition of a mixture is not fixed.

▫ Heterogeneous Mixtures - The parts of the mixture are noticeably different from one another. Examples: salads, salsa

Mixtures▫Homogeneous Mixtures - The substances

are so evenly distributed that it is difficult to distinguish one substance in the mixture from another. Examples: steel, salt water

Solutions, Suspensions, and Colloids

Solutions, Suspensions, and Colloids•Based on the size of its largest particles, a

mixture can be classified as a solution, suspension, or colloid.▫ Solution- Substances dissolve and form a

homogeneous mixture. Examples: tap water, windshield-wiper fluid.

▫ Suspensions- Heterogeneous mixture that separates into layers over time. Examples: sand and water, oil and vinegar.

Solutions, Suspensions, & Colloids• Colloids- Contains some particles that are

intermediate in size between the small particles of solutions and the large particles of suspensions. Colloids will not separate and cannot be filtered. However, colloids will scatter light. (Tyndall Effect) Example: fog.

Tyndall Effect

2.2

Section 2: Physical Properties

•Let’s play 20 Questions!QUESTIONS QUESTIONS

Section 2.2 Physical Properties•Physical property- Any characteristic of a

material that can be observed or measured without changing the composition of the substance in the material. Examples: viscosity, conductivity, malleability, hardness, melting point, boiling point, and density.

Physical Properties•Viscosity- The tendency of a

liquid to keep from flowing. A resistance to flowing. Example: Honey has a high viscosity.

•Conductivity- A material’s ability to allow heat to flow. Example: Metal spoon over a stove.▫Materials with a high

conductivity are called conductors. They are also a good conductor of electricity as well. Wood is a poor conductor.

Physical Properties•Malleability- The ability of a solid to be

hammered into thin sheets without shattering. Example: Most metals can be made into coins or foil.

Because gold is both malleable and beautiful, it is often used to make jewelry. These ancient gold medallions were made to form a necklace

Physical Properties• Hardness- One way to compare harness

of two materials is to see which of the materials can scratch the other. Stainless steel knife blades can scratch copper. Diamond is the hardest known material.

This Tlingit carver is using an adze to carve a canoe from Western red cedar. Red cedar is a relatively soft wood

Physical Properties• Melting Point- Temperature at which a substance

changes from a solid to a liquid. Example: Ice melts because the melting point of water is 0ºC (32ºF).

•  Boiling Point- Temperature at which a substance changes from a liquid to a gas or vapor.

The table lists the melting points and boiling points for several substances.

Physical Properties

• Density- Ratio of the mass of a substance to its volume. This can be used to test the purity of a substance. Examples: Silver has a density of 10.5 g/cm3.

Section 2: Physical Properties

•Density▫Describes the relationship between mass

and volume Density is the amount of matter in a given

amount of space, or volume

GOLF46 grams

PING PONG2 grams

Section 2: Physical Properties

•Solving for Density (d)

•Density can help identify substancesDensities of Common Substances

SUBSTANCE DENSITY (g/cm3) SUBSTANCE DENSITY (g/cm3)

Helium (gas) 0.00001663 Zinc (solid) 7.13

Oxygen (gas) 0.001331 Silver (solid) 10.50

Water (liquid) 1.00 Lead (solid) 11.35

Pyrite (solid) 5.02 Mercury (liquid) 13.55

DENSITY = MASS VOLUME

Section 2: Physical Properties

•Sample problem: What is the density of an object whose mass is 25g and whose volume is 10 cm3?

•Step 1: Write the formula

DENSITY = MASS

VOLUME

Section 2: Physical Properties

•Sample problem: What is the density of an object whose mass is 25g and whose volume is 10 cm3?

•Step 2: Identify the variables

25 g10 cm3

Section 2: Physical Properties

•Sample problem: What is the density of an object whose mass is 25g and whose volume is 10 cm3?

•Step 3: Put numbers in the equation

DENSITY = 25 g 10 cm3

Section 2: Physical Properties

•Sample problem: What is the density of an object whose mass is 25g and whose volume is 10 cm3?

•Step 4: Solve and circle answer

NO NAKED NUMBERS!

!

DENSITY = 25 g 10 cm3

Density= 2.5 g/cm3

Using Physical Properties•Physical properties are used to identify a

material, to choose a material for a specific purpose, or to separate the substances in a mixture. ▫Using properties to identify materials

First, decide which properties to test Second, do tests on the unknown sample Third, compare results with a known sample (This is used in crime scene investigations)

▫Using properties to choose materials Properties determine which materials are

chosen for which uses. Example: shoelaces wouldn’t be made from wood.

Using Physical Properties▫Using properties to

separate mixtures Filtration and distillation

are two common separation methods. Filtration- A process that

separates materials based on the size of their particles. Example: brewing coffee

Distillation- A process that separates the substances in a solution based on their boiling points.

Example: Separate freshwater from seawater.

Recognizing Physical Changes•Physical change- Occurs when some of

the properties of a material change, but the substances in the material remain the same. Examples: cutting paper, melting butter.

Braiding hair and cutting hair are examples of physical changes. Braiding is a reversible change. Cutting cannot be reversed

Physical & Chemical Properties

2.3 Chemical Properties•Chemical property- Any ability to produce a

change on the composition of matter. •Chemical properties can only be observed

when the substances in a sample of matter are changing into different substances. Examples: flammability and reactivity.

Chemical Properties

•Flammability- A material’s ability to burn in the presence of oxygen. Examples: Anything that can be used as a fuel. Wood, gas, paper.

•Reactivity- Describes how readily a substance combines chemically with other substances. Example: Iron with oxygen and water will form rust. If you leave your bike out in the rain.

Recognizing a Chemical Change•Chemical change- Occurs when a

substance reacts and form one or more new substances. Examples: baking cakes, food digesting.

•Three common types of evidence for a chemical change are a change in color, production of a gas, and formation of a precipitate.

Evidence for a Chemical Change

•Color Change▫Silver bracelets will darken.▫Matches burn and turn black.▫Copper roofs turn green.

Evidence for a Chemical Change•Production of a gas

▫Mixing vinegar with baking soda (carbon dioxide gas)

▫Cakes have gas bubbles in it

Gummy bear

Evidence for a Chemical Change•Formation of a

precipitate▫Precipitate-

Solids form and separate from a liquid mixture

▫Curdling of milk- adding lemon juice

Physical & Chemical Properties Song

Is a Change Chemical or Physical?• Sometimes gas bubbles or color change is not a chemical

change. You must ask yourself: Are different substances present after the change takes place.

• 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.

A blacksmith uses a hammer to shape a horseshoe that has been heated. Although the color of the iron horseshoe changes, no chemical change is occurring