Compounds Student Learning Objectives: define what a compound is define what a compound is compare elements and compounds compare elements and compounds describe how compounds differ from the elements they are made from describe how compounds differ from the elements they are made from 1

Matter Concept Map MATTER Can it be physically separated? Homogeneous Mixture (solution) Heterogeneous MixtureCompound Element MIXTUREPURE SUBSTANCE yesno Can it be chemically decomposed? noyes Is the composition uniform? noyes ColloidsSuspensions 2

What do these have in common? ElementCompound What is different about them? Discuss with your partner. 3

Pure Substance Pure Substance  Substance in which there is only one type of particle  Particles are the same as other particles in that substance. Element particle  atom Element particle  atom Compound particle  molecules Compound particle  molecules Water is a compound because it is made of molecules that are all the same. Water is a compound because it is made of molecules that are all the same. 4

Elements  Pure substance that cannot be broken down into simpler substances by chemical or physical means.  Composed of the same atoms.  Represented by a chemical symbol 5

Compounds  Two or more elements that are chemically combined and can be broken down  Pure substances, made of molecules  Represented by a chemical formula: water = H 2 O water = H 2 O 6

Compounds have a Specific Ratio of Elements  The molecules have same number of atoms of each element that makes up the formula.  The subscript tells the number of atoms of each element in the molecule Examples: Water: H 2 O = 2 H atoms and 1 O atom Water: H 2 O = 2 H atoms and 1 O atom Peroxide: H 2 O 2 = 2 H atoms and 2 O atoms Peroxide: H 2 O 2 = 2 H atoms and 2 O atoms Carbon dioxide: CO 2 = 1 C atoms and 2 O atoms Carbon dioxide: CO 2 = 1 C atoms and 2 O atoms Carbon monoxide: CO = 1 C atom and 1 O atom Carbon monoxide: CO = 1 C atom and 1 O atom  Different ratio of the same elements makes a different compound 7

Compounds have Unique Properties  Compounds and their elements have different properties Na + Cl = NaCl (salt) Na + Cl = NaCl (salt) (soft, silvery, reactive metal) + (green poisonous gas) = (white, crystalline, edible solid)  Compounds can be identified by their properties Salt is a white crystalline solid with a high mp Salt is a white crystalline solid with a high mp 8

Discuss  2H  2H 2 O  Discuss with your partner the properties of hydrogen and oxygen and how they compare to the properties of water  Hydrogen: clear, colorless, odorless, explosive gas  Oxygen: clear, colorless, odorless gas that supports burning  Water: clear, colorless, odorless liquid that is used to put out fires. 9

Compounds CAN Be Broken Down  Compounds can be broken down by chemical change such as Chemical reactionChemical reaction HeatingHeating ElectrolysisElectrolysis  Compounds cannot be broken down by physical change such as crushing or boiling.crushing or boiling. 10

Discuss  Discuss with your partner what happens when you boil water? Is boiling a physical or chemical change?  When water is boiled, it changes to water vapor (same substance, H 2 O) so boiling is a physical change. 11

Ionic Compounds  Metal + nonmetal  Electrons are transferred from metal to nonmetal forming + and - ions  Opposite charges attract  Formula: + ion comes first  Properties of ionic compounds: Hard, brittle, high MP & BP 12

Discuss  Discuss examples of ionic compounds with your partner.  Examples: Na + Cl - or NaCl Sodium Chloride Na + Cl - or NaCl Sodium Chloride Mg +2 O -2 or MgO Magnesium Oxide Mg +2 O -2 or MgO Magnesium Oxide Li 2 +1 S -2 or Li 2 S Lithium Sulfide Li 2 +1 S -2 or Li 2 S Lithium Sulfide 13

Covalent Compounds  Nonmetal + nonmetal  NO ions formed  Electrons are shared  Soft, Low MP and BP  Discuss examples with your partner CO 2 Carbon dioxide CO 2 Carbon dioxide H 2 O Water (Dihydrogen monoxide) H 2 O Water (Dihydrogen monoxide) NH 3 Ammonia (Nitrogen trihydride) NH 3 Ammonia (Nitrogen trihydride) 14

321 Review  Complete the 321 Review 15