Prentice Hall Physical Science Chapter 2 Properties of Matter 2.1 Classifying Matter Composition is what the material is made of Composition determines if a material is a pure substance or a mixture A. Pure Substances • Matter that is exactly the same throughout is a pure substance; it has the same composition throughout 1. Elements • - a substance that cannot be broken down into simpler substances • it contains only one type of atom; all of the atoms in a sample of an element are exactly the same • at room temperature, most elements are solids • each element name is represented by a symbol • - each symbol is one or two letters and the first letter is always capitalized • - ex: sodium is Na • carbon is C • gold is Au • 2. Compounds • a substance made of two or more simpler substances (elements or other, simpler compounds) that be broken down into those substances with a chemical reaction • the properties of the compounds are different than the properties of the elements that make them up B. Mixtures • Mixtures are combinations of two or more substances where each substance maintains its own properties The properties vary The composition varies because the substances can be mixed in any proportion Mixtures CAN be separated into their part without a chemical reaction • 1. heterogeneous mixtures – the parts of the mixture are noticeably different from one another (ex: beach sand, chili, vegetable soup) • 2. homogeneous mixtures – the parts of the mixture cannot be distinguished from one another (ex: alloys, ocean water, cake batter) • 3. solutions – substances that dissolve to form a homogeneous mixture (ex: salt water, kool-aid) • liquid solutions do not separate and cannot be filtered • light passes straight through them without being scattered • the particles in them are too small to settle or be trapped • 4. suspensions – a heterogeneous mixture that separates into layers over time (ex: muddy water, Italian salad dressing) • a filter can separate the parts • the particles are too larger to dissolve or be trapped • 5. colloids – contains particles that are intermediate in size caught between smaller particles (homogenized milk) • the particles do not settle out Prentice Hall Physical Science Chapter 2 Properties of Matter 2.2 Physical Properties A physical property is one that can be observed or measured without changing the composition of the material A. Examples of Physical Properties • Viscosity – the tendency of a liquid to keep from flowing (resistance to flow) • the greater the viscosity, the slower the liquid flows ex: honey has a very high viscosity, water has a low viscosity viscosity decreases as a liquid is heated • Conductivity – a material’s ability to allow heat to flow through it • materials with a high conductivity are called conductors and will get hot when heated (ex:metals) a material that is a good conductor of heat is usually a good conductor of electricity • 3. Malleability – the ability of a solid to be hammered with out shattering (ex: metals) • 4. Hardness • 5. Melting and Boiling point • • • - melting point is the temperature at which a solid changes to a liquid boiling point is the temperature at which a liquid changes to a gas by boiling each substance has its own unique melting and boiling point (fig. 12, p. 47) 6. Density – mass/volume • can be used to test the purity of a substance because each substance has its own unique density • B. Using Physical Properties - physical properties are used to identify a material, choose a material for a specific purpose, or to separate the substance in a mixture • - Using Properties to Identify Materials • - perform tests on an unknown sample and compare the result with data for known materials to see if they match - Using properties to choose materials • - if you know what you want a material to do, you can choose materials that have those properties C. Using Properties to Separate Mixtures - Filtration - uses the sizes of particles to separate them - large particles are caught in the filter paper, strainer, etc. - Distillation - separates substances based on their boiling points • - ex: a mixture of alcohol and water can be separated by boiling the mixture. Since alcohol and water have different boiling points, the one with the lower boiling point will boil first. Its gas can be collected, cooled until it becomes liquid again. D. Recognizing Physical Changes • a physical change is one in which some of the properties of a material may change, but the substances stay the same; the chemical composition stays the same • a lot of physical changes can be reversed • ex: freezing water, sawing a log, crashing a car, cutting hair Prentice Hall Physical Science Chapter 2 Properties of Matter 2.3 Chemical Properties a chemical property is the ability to cause a change in the composition of matter; it is how one substance interacts with another chemical properties can only be observed when a substance is changing into a different substance A. Observing Chemical Properties - Flammability – the ability to burn in the presence of oxygen • - Reactivity – how readily a substance combines chemically with another substance - ex: oxygen is highly reactive, nitrogen is not very reactive B. Recognizing Chemical Changes • a chemical change occurs when a substance reacts to form one or more new substances (ex: iron rusting, paper burning, baking soda and vinegar giving off a gas) changing color, producing a gas, and forming a precipitate are all evidence tat a chemical change has taken place • a precipitate is a solid that forms and separates from a liquid mixture C. Is a Change Chemical or Physical? • Are different substance present after the change or is it still the same material? Ex: burning paper • • • • Cutting down a tree Coloring hair Painting a house Sugar dissolving in water