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Matter Objectives

•Learn about the composition of matter. •Learn the difference between elements and compounds. •Learn to distinguish between physical and chemical properties and changes. •Learn to distinguish between mixtures and pure substances. •Learn two methods of separating mixtures.

The Particulate Nature of Matter

• Matter - Anything that has mass and occupies space. – All matter consists of tiny particles called atoms.

– We can only “see” atoms with powerful electronic microscopes.

• Mass - A measure of the quantity (amount) of matter in an object. – NOT the same as weight; we use grams.

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Elements & Compounds

• Atom - The smallest unit of an element that maintains the properties of that element. – Not all atoms are alike.

– There are a little over 100 different types.

• Element - A pure substance made of only one kind of atom. – Scientists use the Periodic Table to group elements.

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Elements & Compounds • Compound – A substance with constant composition that can be broken down into elements by chemical processes. – A compound always contains atoms of different

elements.

• Molecule - A bonded collection of two or more atoms of the same element or different elements. – Just as we can use a few letters to make thousands of

words, all matter is constructed from a few types of atoms.

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Compounds - Atom Combinations

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The States of Matter • Solid - Has a definite (fixed) shape and volume (cannot flow).

• Liquid - Definite volume but takes the shape of its container (flows).

• Gas – Has neither fixed shape nor fixed volume (flows).

• Plasma - High temperature, ionized phase of matter as found on the sun and other stars.

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States of Matter • The three states of water have distinctly different properties.

• All substances, like water, exist in the three states of matter.

• Solids and liquids are not really compressible while gases are.

• Vapor - A substance that is currently a gas but normally is a liquid or solid at room temperature.

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Physical & Chemical Properties and Changes

• Physical Property - A characteristic of a substance that can change without the substance becoming a different substance. – Some typical physical properties include a given substance’s odor, color, volume, state, density, melting point, and boiling point.

• Chemical Property - The ability of a sub-stance to change to a different substance. – Examples include a substance’s ability to rust, combust or react in some way. 2-8

Practice • Classify each of the following as a physical or a chemical property: – The boiling point of an alcohol is 78 °C

– Diamond is very hard

– Sugar ferments to form alcohol

– A metal wire conducts an electric current

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Physical & Chemical Changes • Physical Change - A change in the form of a substance, but not in its chemical nature; chemical bonds are not broken. – Phase changes such as melting and sublimation are examples of physical changes.

• Chemical Change - A change of substances through a reorganization of the atoms to fundamentally different substances; a chemical reaction. – The original substance no longer exists. – Electrolysis, burning fuel, and digesting food are a few examples of chemical changes. 2-10

Practice • Classify each of the following as a physical or a chemical change: – Iron metal is melted

– Iron combines with oxygen to form rust

– Wood burns in air

– A rock is broken into small pieces

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Mixture and Pure Substances

• Mixture - A material of variable composition that contains two or more substances. – While the composition of a mixture may vary, the composition of its compounds will always stay the same.

– For example, you can vary the amount of water or sugar when you make Kool-Aid, but the water will remain water and the sugar will remain sugar.

– The air we breathe is a mixture. 2-12

The composition of air.

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Chart examining

each substance of air.

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Mixtures and Pure Substances • Alloy - A substance that contains a mixture of elements and has metallic properties. – Some examples of alloys include Sterling silver (93% silver and 7% copper), pewter (85% tin, 7% copper, 6% bismuth, and 2% antimony).

– Brasses and bronzes are alloys of copper and zinc.

– Gold also has many different alloys.

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Twenty-four-karat gold is an element. Eighteen-karat gold is an alloy. Fourteen-karat gold is an alloy.

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Mixtures and Pure Substances

• Pure Substance - A substance with constant composition. – May either be elements or compounds..

– The properties of a pure substance make it possible to identify that substance conclusively.

– In theory mixtures can be separated into pure substances: elements and/or compounds.

– In reality, no matter how hard we try, some impurities will remain in each of the “pure substances.” 2-17

Representation of H2O molecules; a pure substance

(compound).

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Homogeneous & Heterogeneous Mixtures

• Homogeneous Mixture - A mixture that is the same throughout; a solution. – Salt water is an example: all regions of the mixture have the same properties.

• Heterogeneous Mixture - A mixture that has different properties in different regions of the mixture. – When sand is poured in water, the mixture has one region containing water and another containing mostly sand. 2-19

Practice • Classify each of the following as a pure substance, a homogeneous mixture, or a heterogeneous mixture: – Maple syrup

– The oxygen and helium in a scuba tank

– Oil and vinegar salad dressing

– Common salt (sodium chloride)

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Separation of Mixtures

• Distillation - A method for separating the components of a liquid mixture that depends on the differences in the boiling points (ease of vaporization) of the components. – Seawater is distilled to purify it. The water is boiled off, captured and condensed back into a liquid leaving the salt behind.

– Usually used when one substance is dissolved in another.

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The solution is boiled and steam

is driven off.

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Salt remains after all water is boiled off.

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No chemical change occurs when salt water is distilled.

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Separation of Mixtures • Filtration - A method for separating the components of a mixture containing a solid (not dissolved) and a liquid. – Usually a heterogeneous mixture.

– The mixture can be separated by pouring over filter paper allowing the liquid to pass through and leaving the solid behind.

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Filtration separates a liquid from a solid.

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Separation of a sand-saltwater mixture.

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