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  with one another. –Cmpd is different from elements that reacted to form it

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 H 2 O = 1:8 –If mass ratio is different, it can’t be H 2 O 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/ H 2 O, Cl is a poisonous gas

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Compounds Compounds Can Be Broken Down into Simpler Substances –Some cmpds broken down into elements thru chemical  ex: Mercury oxide  heated  Hg + O ex: electric current & NaCl  Na + Cl –Some cmpds go thru chemical  s to form simpler cmpds. These are broken down further by additional chemical  s. ex: carbonic acid (carbonated “fizz”)  CO 2 + H 2 O  C + O + H –Cmpds can’t be broken down by physical  s. There’s ONLY ONE way… thru chemical  ! –H 2 O thru a filter doesn’t  H 2 O –Grinding a solid doesn’t  the solid

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 –CO 2 »Made by cells in metabolism  humans exhale »Plants take in thru photosynthesis to make sugars & other cmpds –Cmpds in industry NH 3, 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