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Ch. 2 - Properties of Matter

Composition à A putting together; combining of parts into a whole. Substances are either pure or mixtures.

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Pure substances = matter that has the same composition throughout; any piece of a pure substance will have the same properties

Two types of pure substances:

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1. Element à Can't be broken down into simplersubstances. The smallest unit of an element is an atom. Elements contain only1 type of atom

EX: aluminum foil, pencil lead (carbon),Oxygen gas, gold

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2. Compounds à a substance that is made from2 or more simpler substances, always in a fixed ratio, and can be broken down into these substances. The properties of a compound are often very different than the properties of its components.

EX: Oxygen and hydrogen are gases, yetproduce liquid water (H20) when combined.

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Mixtures = Combination of different substances; the ratio of these substances can vary; the properties will vary based on the distribution of the components.

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Two types of mixtures:

1. Heterogeneous mixture à the parts of the mixture are noticeably different from eachother. (hetero = different, genus = kind)

EX: sand, salsa, Chex mix

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2. Homogeneous mixture à substances are soevenly distributed that the mixture appearsthe same throughout - appears to only containone substance.

EX: Pepsi, swimming pool water, stainless steel and other alloys

Some substances are more difficult to classify!

The size of the particles in a mixture can affect the properties of the mixtures. We classify these mixtures based on the size of the largest particles:

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1. Solutions à a homogeneous mixtures where onesubstance is completely dissolved in another. These:

~don't separate into distinct layers over time, ~ can't be filtered, and don't scatter light. ~Has the smallest particles. Ex: salt water, Kool-Aid, tap water

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2. Suspensions à a heterogeneous mixtures thatseparates into layers over time, can befiltered and can scatter light (whichis why they appear cloudy). Has thelargest particles.

Ex: dust in air, sand in water

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3. Colloids à contains medium sized-particles thatdo not separate into layers, can't befiltered and DOES scatter light.

Ex: Fog in air, homogenized milk

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Section 2.2 - Physical Properties

Physical property = a characteristic of a material that can be measured or observed withoutchanging the composition of the material.

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Types of physical properties: 1. viscosity = resistance of a liquid to flowing. As a substance is heated, what usually happens to viscosity?

2. conductivity = ability to allow heat to flow. Metals are usually good heat conductors (as well as good electrical conductors), while wood is a poor conductor

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3. malleability = ability of a metal to be hammered without shattering. Most metals are malleable (whereas glass is not!)

4. hardness = ability to scratch another substance. Diamonds are the hardest known material.

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5. melting and boiling points = melting point is when a substance changes from solid to liquid; boiling point is when a substance changes from liquid to gas.

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6. Density = ratio of the mass of a substance to its volume. Can be used to determine the purity of a substance (its how nuggets were determined to be gold back during the gold rush!)

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Physical properties can be used to:1. Identify a materialà decide the properties to test, test theunknown, compare results to known results(this is how much crime scene evidence isidentified!)

2. Choose a material for a specific purposeà read about how sculptures are made on p.

49!3. To separate the substances in a mixtureà Filtration = separates materials based on the size of their particlesà Distillation = separates substances of a

solution based on their boiling points.

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If you were stranded on a boat, how could you use physical properties to separate the materials in salt water to obtain fresh drinking water?

Where do we get our drinking water from?

Analyze the diagram on p. 52-53 and write a short explanation of the steps involved in purifying drinking water.

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Section 2.3 - Chemical Properties

Chemical property = can be observed only when the substances in a sample of matter are changing into different substances.

Types of chemical properties:

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1. Flammability à material's ability to burn in the presence of oxygen

EX: gasoline, wax, paper

2. Reactivity à how readily a substance combines chemically with other substances.

EX: oxygen is highly reactive, while nitrogen is not

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What substance reacts with oxygen to form rust?

What would be a way to prevent iron ships, that often store seawater in the bottom of their decks to help maintain balance, from rusting on the inside?

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Chemical changes à a substance reacts and forms one or more new substances.

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Signs of chemical changes include:

1. Change in color = silver tarnishing, copper "greening"

2. Production of gas = bubbles form; cake rises, vinegar + baking soda = gas production

3. Formation of a precipitate = a solid forms and separates from a liquid mixture; milk curdling

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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.

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