Properties or Matter

2.1 Classifying Matter Why are elements and compounds classified as pure substances? How do mixtures differ from pure substances? What is the main difference among solutions, suspensions, and colloids?

Pure Substances = substances -matter that has exactly the same composition (fixed and uniform) -table salt and table sugar Compound: Dry Ice Element: Gold Matter can be pure, such as an element (gold), or a compound (water).

Elements Cannot be broken down into simpler substances by ordinary chemical changes Only about 100 known An atom is the smallest particle of an element that has the chemical properties of that element. (An element consists of atoms of only one type.) At room temperature, most elements are solids. Al - Aluminum (aluminum foil, soft drink cans) C- Carbon (main element in pencil lead) Some elements are gases at room temp. Oxygen and nitrogen Two elements are liquids at room temperature Bromine and mercury (both extremely poisonous) Turn to page 39 in your textbook. What are some characteristics of the elements pictured here?

Elements are represented by Symbols 1813 - Jons Berzelius (Swedish chemist) suggested chemists use symbols (Class participation points opportunity!!!) Symbols allow scientists to communicate without confusion (regardless of language)

A molecule is a group of atoms that are held together by covalent bonds so that they move as a single unit.

Compounds A substance made from two or more simpler substances joined in a fixed proportion (A substance made up of two or more different types of atoms bonded together.) Water (H2O) Properties differ from those of the substances from which the compound is made O and H are gases at room temperature, H can fuel fire, O can keep it burning Water is a liquid at room temperature but does not burn or help other substances to burn

Comparing and Contrasting Molecules and Compounds

Coming Soon!

Mixtures Properties can vary Composition is not fixed Matter can be a mixture. Mixtures are a combination of two or more substances that do not combine chemically but remain the same individual substances. Mixtures can be separated by physical means. Mixtures contain two or more pure substances. Properties can vary can retain some properties of their individual substances but properties are less constant than properties of a substance Composition is not fixed Think of a salad Heterogeneous and Homogeneous Mixtures Hetero – parts are noticeably different(sand=light and dark parts) Homo – parts are difficult to distinguish(stainless steel=iron, chromium and nickel) How can you tell sand is a heterogeneous mixture?

Mixtures can be solutions, suspensions and colloids Mixtures can be solutions, suspensions and colloids. Mixtures are classified by the size of their largest particles. Solutions – sugar water, windshield wiper fluid –homogenous mixture –will not separate over time Suspensions – sandy water, Italian salad dressing – heterogeneous mixture – separates into layers over time – scatters light Colloids – fog, homogenized milk – homogeneous or heterogeneous depending on approach – water, sugar, proteins, fats – do not separate into layers *What happens to suspended particles over time? *How does a mask prevent a worker from inhaling particles of plastic suspended in the air after they’ve been sanded from a surfboard ? *Consider creating a three part Venn diagram on mixtures.

Delving Deeper into Mixtures Solutions Suspensions Colloids A solution is a homogeneous mixture of two or more components. The dissolving agent is the solvent. The substance which is dissolved is the solute. The components of a solution are atoms, ions, or molecules, which makes them 10-9 m or smaller in diameter. The particles in suspensions are larger than those found in solutions. Components of a suspension can be evenly distributed by a mechanical means, like by shaking the contents, but the components will settle out. Particles intermediate in size between those found in solutions and suspensions can be mixed such that they remain evenly distributed without settling out. These particles range in size from 10-8 to 10-6 m in size and are termed colloidal particles or colloids. The mixture they form is called a colloidal dispersion. A colloidal dispersion consists of colloids in a dispersing medium. Example: Oil and water, Fine sand in water, Paint, Dust in air, Droplets of oil in air Examples: Sugar dissolved in water, Salt dissolved in water Carbon dioxide or oxygen in water, Water vapor in air, Hexane in paraffin wax, Mercury in gold Example: Aerosol (liquid dispersed in a gas - fog, mist, clouds) Foam (gas dispersed in a liquid - soda (CO2 dissolved in water), whipped cream) Solid Foam (gas dispersed in a solid - Styrofoam, plaster) Emulsion (liquid dispersed in a liquid - butter, milk)

Processing the Concepts

Matter Anything with mass and volume. Substance Matter with constant composition Mixture Matter with variable composition Element Substance made up of only one type of atom Compound Two or more elements that are chemically combined Heterogeneous Mixture Mixtures that are made up of more than one phase Homogeneous Mixtures Also called solutions. Mixtures that are made up of only one phase Examples - gold, silver, carbon, oxygen and hydrogen Examples - water, carbon dioxide, sodium bicarbonate, carbon monoxide Examples - sand, soil, chicken soup, pizza, chocolate chip cookies. Examples - salt water, pure air, metal alloys, seltzer water.

Data Analysis: Do the Contents of Two Cans of Mixed Nuts meet FDA Regulations? (p 42) How are the two brands of mixed nuts alike? How are they different? What is the percent by mass of each type of nut in each can? Do the contents of each can meet the FDA regulations? Explain On the Brand A label, the nuts are listed in this order: peanuts, Brazil nuts, almonds, cashews, pecans, and hazelnuts. What do you think determines the order?

2.2 Physical Properties When can physical properties be observed? What observations might indicate that a physical change has occurred?

A physical property is any characteristic of a material (substance) that can be observed or measured without changing the compositions (identities) of the substances in the material. (See pages 45-47.) Viscosity Conductivity Malleability Hardness Melting point Boiling point Density Consider a Layered Foldable Reflection

Using Physical Properties To Identify Materials To Choose Materials To Separate Mixtures Filtration Distillation

• Physical properties can be observed without changing the substance. • Physical changes can change some physical properties but do not change the substance.

Recognizing Physical Changes Some of the properties change but substances in the material remain the same Water Liquid Gas Butter (solid) in a pan (heated) liquid butter Crumpling or slicing changes size and shape but not composition Some physical changes can be reversed and others cannot (braids and ice, verses sliced tomatoes or peeled oranges)

2.3 Chemical Properties When can chemical properties be observed? What observations might indicate that a chemical change has occurred? What is the difference between chemical and physical changes?

Observing Chemical Properties Chemical properties have the ability to produce a change in the composition of matter. Can only be observed changing into different substances Flammability (combustion) Reactivity rusting(oxidation) tarnishing

Recognizing Chemical Changes Change in color Production of a gas Forming a precipitate

Comparing and Contrasting Physical and Chemical Properties Do you have ideas for how this information could be organized using a tool a scientist might use? Physical or chemical change?

Compare and Contrast Physical or Chemical Changes Use a Venn Diagram, Table or T – chart One Example: Physical Change Chemical Change Composition of matter remains the same Composition of matter changes Some can be reversed and some cannot Can be reversed but it’s not easy

What Should Be Done With Arsenic-Treated Wood? Another opportunity for class participation credit… Read Research Complete a Current Event form