chapter 3 elements, compounds & mixtures. compounds compound = pure substance composed of >2...
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Chapter 3Elements, 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 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
http://www.youtube.com/watch?v=fLJ4FH7q0EQ
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”)
CO2 + H2O C + O + H
– Cmpds can’t be broken down by physical s.• There’s ONLY ONE way… thru chemical
!– H2O thru a filter doesn’t H2O– 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
– 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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