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Ch. 4 Section 1 Substance either an element or a compound cannot be broken down into simpler components and still maintain the properties it had originally Element- a substance in which all atoms are alike Elements in nature are stable Elements from labs are unstable - exist only for short periods of time Aluminum- can be used as a blanket because it reflects radiation (a form of heat) Americium- used in smoke detectors- radioactive Tungsten- very high melting point- used in lightbulb filaments Titanium- very lightweight and strong metalused in frames for airplanes and in engines Lead- high density- makes it a good barrier for radiation- blocks particle movement Gold- used for coating space vehicles and other electronics Resists corrosion & reflects infrared Compounds- substance in which the atoms of two or more different elements are combined in fixed proportions Elements bond to form compounds Cannot be separated by physical means C Element - Atom S8 Element- Molecule H2O Compound Cl2 Element- Molecule H2O2 Compound Mixture- made up of two or more substances- can be separated by physical means Heterogeneous-made of materials that can be distinguished from each other Not uniform in composition Homogenous- contains two or more gaseous, liquid, or solid substance blended evenly throughout Solution- homogeneous mixtures containing particles so small they cannot be seen with a microscope and will never settle to the bottom of the container- tap water, salt water, food coloring and water Colloid- mixture with large particles that never settlefog, smoke, ink, glue, milk, cream, butter Colloid vs. Solution-pass a beam of light through the mixture If the beam is invisible- it is a solution If the beam is visible- it is a colloid The visible beam through the colloid is called the Tyndall effect Suspension- heterogeneous mixture containing a liquid in which visible particles settle out over time – like dirty water http://www.docbrown.info/page12/gifs/Ele CpdMixALL.gif How can you tell the difference between mixture and compound? Mixture can be separated physically and keep its properties Compound can only be separated chemically and does NOT keep its properties Ch. 4 Section 2 Physical Property- any characteristic of a material that you can observe or attempt to observe without changing the identity of the substance For example: color, shape, size, melting point, and boiling point. Behavior of substances- magnetism, ductility- ability of metal to be drawn into wires; malleabilityability of metal to be shaped- pounded into sheets; ability to flow Physical Change- IDENTITY DOES NOT CHANGE a change in size, shape, or state of matter may or may not involve energy changes and color changes Distillation- separating a mixture through evaporating a liquid and re-condensing its vapor. Vapors from the liquid with the lowest boiling point form first and are condensed and collected Chemical Property- characteristic of a substance that indicates whether it can undergo a certain chemical change Chemical Change- change in identity- changes the COMPOUND or SUBSTANCE Dark bottles- block light- prevents change in identity Indications that a chemical change MAY have occurred: Smell, heat, light, sound, color change, production of gas or precipitate Color change does not always indicate a chemical change Example: blue and yellow make green- physical change- just a mixture http://www.ric.edu/faculty/ptiskus/chemica l/ Chemical changes can be used to separate substances- done in labs- metals can be removed from ore this way Weathering Physical change when rocks split as water freezes or as erosion occurs Chemical change when acidic water reacts with limestone and results in a new substance that dissolves in water and washes away. Mass cannot be created or destroyed Burning a log seems to make mass disappear “missing” mass is actually present in the gases that are produced as the log burns http://www.quia.com/quiz/303980.html