compunds ch4.2 8th pdf

8/14/2019 Compunds Ch4.2 8th PDF

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Chapter 4 Section 2


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Objectives Explain how elements make up compounds

Describe the properties of compounds

Explain how a compound can be broken down into itselements

Give examples of common compounds


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Compounds: Made of Elements Most elements take part in chemical changes fairly

easily

Elements are rarely found alone in nature

Elements combined chemically with other elements

form compounds


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Compounds continuedA particle of a compound is called a molecule

Molecules of compounds form when atoms of 2 ormore elements join together


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Water (H20)

http://sayee.ca/image/water%20molecule.gif


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Properties of Compounds Each compound has its own physical and chemical

properties

Ex: hydrogen peroxide (H202) Why are hydrogen peroxide bottles opaque (dark

brown)?

http://www.passionatehomemaking.com/wp-content/uploads/2009/04/fam_hydrogen_peroxide_pint-4080.jpg

http://www.umesc.usgs.gov/aquatic/drug_research/hydrogen_peroxide/hydrogen_peroxide_structure_400.gif


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Properties:

Compounds vs. Elements Properties of compounds differ from elements they are

formed from

Ex: Table salt (NaCl)

Sodium reacts violently with water

Chlorine is a poisonous gas

Combined chemically, they are safe to eat! Dissolves in water without exploding

http://www.usavsus.info/Images6/S070327-02L.jpg


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Breaking Down Compounds Some compounds can be broken down by chemical

changes into simpler compounds or elemental form

Ex: Carbonic acid (gives soda its fizz)

When the can is opened, carbonic acid breaks down into

Carbon dioxide (C02) and water (H2O)

Co2 and H2O can be broken down further into theelements (C, H, O)


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Methods of Breaking Down

Compounds

Add energy

Heat energy

Electric current


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Compounds in your World In industry:

Aluminum (makes cans & airplanes)

Not found alone in nature

Aluminum Oxide (Al2O3) broken down

Ammonia (make fertilizers)

Combining elements nitrogen and hydrogen (NH3 )


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Compounds in Nature Proteins found in all living things

Nitrogen

Carbon dioxide (C02) important roles in life Carbon, Oxygen


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Quick Quiz

Compounds cannot be broken down by any means

(True/False?)

Compounds can be broken down only by chemicalchanges (True/False?)

Heating can break down some compounds(True/False?)

compunds ch4.2 8th pdf

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