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