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Chapter 3

Chapter 3. Elements, Compounds & Mixtures. Compounds. compound = pure substance composed of > 2 elements that are chemically combined particle is formed when atoms of > 2 elements join together For elements to combine, they must react or undergo chemical D with one another.

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Chapter 3

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  1. Chapter 3 Elements, Compounds & Mixtures

  2. Compounds • compound = pure substance composed of >2 elements that are chemically combined • particle is formed when atoms of >2 elements join together • For elements to combine, they must react or undergo chemical D with one another. • Cmpd is different from elements that reacted to form it

  3. Compounds • Elements Combine in a Definite Ratio to Form a Cmpd • Not random combinations! • Elements join in specific ratio according to their masses • ex: mass of H & O for H2O = 1:8 • If mass ratio is different, it can’t be H2O • Every Compound Has a Unique Set of Properties • These allow you to distinguish them from other cmpds • Ea cmpd has its own physical properties – boiling/melting pt, density, color • Cmpds are ID’d by their chemical properties – reactivity with acid, reactivity when exposed to light • Cmpd has different properties than the elements that form it • Original elements lose their properties • NaCl – Na reacts violently w/ H2O, Cl is a poisonous gas

  4. http://www.youtube.com/watch?v=fLJ4FH7q0EQ

  5. Compounds • Compounds Can Be Broken Down into Simpler Substances • Some cmpds broken down into elements thru chemical D • ex: Mercury oxide  heated  Hg + O • ex: electric current & NaCl  Na + Cl • Some cmpds go thru chemical Ds to form simpler cmpds. These are broken down further by additional chemical Ds. • ex: carbonic acid (carbonated “fizz”)  CO2 + H2O  C + O + H • Cmpds can’t be broken down by physical Ds. • There’s ONLY ONE way… thru chemical D! • H2O thru a filter doesn’t D H2O • Grinding a solid doesn’t D the solid

  6. Compounds • Compounds in your world • Cmpds in nature • proteins – in all living things • N is needed to make proteins • Plants get N thru root structures, soil • Animals eat plants or other herbivores  nutrients are broken down into smaller cmpds thru digestion  yielding N • CO2 • Made by cells in metabolism  humans exhale • Plants take in thru photosynthesis to make sugars & other cmpds • Cmpds in industry • NH3, ammonia • fertilizers  source of plant N • Also medicines, food preservatives, synthetic fabrics • Cmpds in nature aren’t usually raw materials needed by industry • Must be broken down to provide elements • ex: Aluminum is found as aluminum oxide naturally & must be separated from oxygen to make it useable

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