CHAPTER 2 PROPERTIES OF MATTER

BASED ON COMPOSITIONS, MATERIALS CAN BE DIVIDED INTO PURE SUBSTANCES OR MIXTURES.

PURE SUBSTANCE – matter that always has exactly the same composition – EVERY SAMPLE OF A GIVEN SUBSTANCE HAS THE SAME PROPERTIES BECAUSE A SUBSTANCE HAS A FIXED, UNIFORM COMPOSITION.

SUBSTANCES CAN BE CLASSIFIED INTO TWO CATEGORIES – ELEMENTS AND COMPOUNDS.

ELEMENT – an element is a substance that cannot be broken down into simpler substances AN ELEMENT HAS A FIXED COMPOSITION BECAUSE IT CONTAINS ONLY ONE TYPE OF ATOM. – NO TWO ELEMENTS CONTAIN THE SAME TYPE OF ATOM.

EXAMPLES OF ELEMENTS – AT ROOM TEMPERATURE MOST ELEMENTS ARE SOLIDS SUCH AS ALUMINUM AND CARBON. GOLD (Au) ALUMINUM (Al) CARBON (C) IODINE (I)

SYMBOLS FOR ELEMENTS – IN 1813 Jons Berzelius suggested that chemists use symbols to represent elements. – EACH SYMBOL HAS ONE OR TWO LETTERS THE FIRST LETTER IS ALWAYS CAPITALIZED THE SECOND LETTER IS ALWAYS LOWER CASE

COMPOUNDS – SUBSTANCE THAT IS MADE FROM TWO OR MORE SIMPLER SUBSTANCES AND CAN BE BROKEN DOWN INTO THOSE SIMPLER SUBSTANCES. – THE SIMPLER SUBSTANCES ARE EITHER ELEMENTS OR OTHER COMPOUNDS – THE PROPERTIES OF A COMPOUND DIFFER FROM THOSE OF THE SUBSTANCES FROM WHICH IT IS MADE EX. WATER (H2O)

A COMPOUND ALWAYS CONTAINS TWO OR MORE ELEMENTS JOINED IN A FIXED PROPORTION. – IF THE PROPORTION CHANGES THEN THE COMPOUND CHANGES.

MIXTURES – MIXTURES RETAIN SOME OF THE PROPERTIES OF THEIR INDIVIDUAL SUBSTANCES – THE PROPERTIES OF A MIXTURE ARE LESS CONSTANT THAN THE PROPERTIES OF A SUBSTANCE. – THE PROPERTIES OF A MIXTURE CAN VARY BECAUSE THE COMPOSITION OF A MIXTURE IS NOT FIXED

MIXTURES cont. – THERE ARE 2 TYPES OF MIXTURES HETEROGENEOUS MIXTURES HOMOGENEOUS MIXTURES

HETEROGENEOUS MIXTURE – THE PARTS OF THE MIXTURE ARE NOTICEABLY DIFFERENT FROM ONE ANOTHER EX. SAND

HOMOGENEOUS MIXTURES – THE SUBSTANCES ARE EVENLY DISTRIBUTED THAT IT IS DIFFICULT TO DISTINGUISH ONE SUBSTANCE IN THE MIXTURE FROM ANOTHER. HOMOGENEOUS MIXTURES APPEAR TO CONTAIN ONLY ONE SUBSTANCE. – EX. WATER IN SWIMMING POOL

SOLUTIONS, SUSPENSIONS, AND COLLOIDS – BASED ON THE SIZE OF ITS LARGEST PARTICLE, A MIXTURE CAN BE CLASSIFIED AS A SOLUTION, A SUSPENSION, OR A COLLOID.

SOLUTIONS – SUBSTANCES THAT DISSOLVE AND FORM A HOMOGENEOUS MIXTURE – SOLUTIONS DO NOT SEPARATE INTO LAYERS OVER TIME. – EX. WIPER FLUID TAP WATER

SUSPENSIONS – HETEROGENEOUS MIXTURE THAT SEPARATES INTO LAYERS OVER TIME. – SUSPENDED PARTICLES SETTLE OUT OF A MIXTURE OR ARE TRAPPED BY A FILTER BECAUSE THEY ARE LARGER THAN THE PARTICLES IN A SOLUTION. – EX. MUDDY WATER

COLLOID – CONTAINS SOME PARTICLES THAT ARE INTERMEDIATE IN SIZE BETWEEN THE SMALL PARTICLES IN A SOLUTION AND THE LARGER PARTICLES IN A SUSPENSION. – THEY DO NOT SEPARATE INTO LAYERS – CANNOT USE A FILTER TO SEPARATE THE PARTS OF A COLLOID – EX. FOG IN THE AIR

VISCOSITY, CONDUCTIVITY, MALLEABILITY, HARDNESS, MELTING POINT, BOILING POINT, AND DENSITY ARE EXAMPLES OF PHYSICAL PROPERTIES.

VISCOSITY – THE TENDENCY OF A LIQUID TO KEEP FROM FLOWING, ITS RESISTANCE TO FLOWING. – THE GREATER THE VISCOSITY THE SLOWER IT MOVES. – VISCOSITY DECREASES WHEN HEATED – VISCOSITY INCREASES WHEN COOLED

CONDUCTIVITY – MATERIALS ABILITY TO ALLOW HEAT TO FLOW – MATERIALS THAT HAVE A HIGH CONDUCTIVITY SUCH AS METALS ARE CALLED CONDUCTORS. – GOOD CONDUCTOR OF HEAT = GOOD CONDUCTOR OF ELECTRICITY

MALLEABILITY – ABILITY OF A SOLID TO BE HAMMERED WITHOUT SHATTERING. – MOST METALS ARE MALLEABLE EX. GOLDSMITHS, BLACKSMITHS – BY CONTRAST, ICE WILL SHATTER WHEN HIT WITH HAMMER.

HARDNESS – THE ABILITY OF ONE MATERIAL TO SCRATCH ANOTHER – STAINLESS STEEL IS HARDER THAN COPPER – DIAMOND IS THE HARDEST KNOWN MATERIAL

MELTING POINT – THE TEMPERATURE AT WHICH A SUBSTANCE CHANGES FROM A SOLID TO LIQUID – EX. ICE MELTING TO WATER

BOILING POINT – THE TEMPERATURE AT WHICH A SUBSTANCE BOILS. – SOME SUBSTANCES CHANGE FROM A LIQUID TO A GAS AT THIS POINT

DENSITY – MASS OF AN OBJECT DIVIDED BY ITS VOLUME – D=M/V – DENSITY CAN BE USED TO TEST THE PURITY OF A SUBSTANCE.

PHYSICAL PROPERTIES ARE USED TO IDENTIFY A MATERIAL,TO CHOOSE A MATERIAL FOR A SPECIFIC PURPOSE, OR TO SEPARATE THE SUBSTANCE IN A MIXTURE.

USING PROPERTIES TO IDENTIFY MATERIALS – STEP 1: DECIDE WHICH PROPERTIES TO TEST EX. DENSITY, MASS, MELTING POINT, BOILING POINT, ETC. – STEP 2: TEST THE UNKOWN SAMPLE – FINAL STEP: COMPARE THE RESULTS WITH THE DATA REPORTED FOR KNOWN MATERIALS

USING PROPERTIES TO CHOOSE MATERIALS – PROPERTIES DETERMINE WHICH MATERIALS ARE CHOSEN FOR WHICH USES. WOODEN SHOELACES METAL TIRES PAPER CHAINS

USING PROPERTIES TO SEPARATE MATERIALS – FILTRATION AND DISTILLATION ARE TWO COMMON SEPARATION METHODS.

FILTRATION – PROCESS THAT SEPARATES MATERIALS BASED ON THE SIZE OF THEIR PARTICLES. – EX. COFFEE FILTERS FILTER COFFEE GRAINS BUT ALLOW CAFFIENE AND SMALLER COFFEE GRAINS TO PASS THROUGH

DISTILLATION – PROCESS THAT SEPARATES SUBSTANCES IN A SOLUTION BASED ON THEIR BOILING POINTS. – EX. BOILING SEA WATER, CAPTURING THE WATER VAPORS, COOLING THE VAPORS AND COLLECTING THEM IN A SEPARATE CONTAINER…THIS PROVIDES FRESH WATER WITHOUT THE SALT.

RECOGNIZING PHYSICAL CHANGES – A PHYSICAL CHANGE OCCURS WHEN SOME OF THE PROPERTIES OF A MATERIAL CHANGE, BUT THE SUBSTANCES IN THE MATERIAL REMAIN THE SAME. EX. METLING BUTTER IN A PAN CAUSES THE BUTTER TO CHANGE FROM A SOLID TO A LIQUID BUT THE SUBSTANCES IN THE BUTTER DO NOT CHANGE. – SOME PHYSICAL CHANGES CAN BE REVERSED AND SOME CANNOT. EX. MELTING ICE AND REFREEZING IT (REVERSED) EX. REPLACING THE PEELING ON AN ORANGE AFTER YOU PEELED IT. (IRREVERSIBLE)

CHEMICAL PROPERTY – THE ABILITY TO PRODUCE A CHANGE IN THE COMPOSITION OF MATTER. – EX. THE ABILITY TO BURN. CHEMICAL PROPERTIES CAN BE OBSERVED ONLY WHEN THE SUBSTANCE IN A SAMPLE OF MATTER ARE CHANGING INTO DIFFERENT SUBSTANCES.

FLAMABILITY – MATERIAL ABILITY TO BURN IN THE PRESENCE OF OXYGEN REACTIVITY – THE PROPERTY THAT DESCRIBES HOW READILY A SUBSTANCE COMBINES CHEMICALLY WITH OTHER SUBSTANCES

RECOGNIZING CHEMICAL CHANGES – A CHEMICAL CHANGE OCCURS WHEN A SUBSTANCE REACTS AND FORMS ONE OR MORE NEW SUBSTANCES. EX. CAKE BAKING IN THE OVEN, LEAVES ON A TREE CHANGING COLORS

RECOGNIZING CHEMICAL CHANGE – THREE COMMON TYPES OF EVIDENCE FOR A CHEMICAL CHANGE ARE A CHANGE IN COLOR, THE PRODUCTION OF A GAS, AND THE FORMATION OF A PRECIPITATE.

A CHANGE IN COLOR – SILVER WILL DARKEN WHEN EXPOSED TO AIR – COPPER WILL CHANGE COLORS (COPPER TO GREEN) A CHANGE IN COLOR IS A CLUE THAT A CHEMICAL CHANGE HAS PRODUCED AT LEAST ONE NEW SUBSTANCE.

PRODUCTION OF GAS – IF THE COMBINATION OF TWO OR MORE SUBSTANCES PRODUCES A GAS A CHEMICAL CHANGE IS HAPPENING. EX. CARBONATION FIZZING IN SOFT DRINKS, BAKING SODA AND VINEGAR

FORMATION OF A PRECIPITATE – HAPPENS WHEN A SOLID FORMS AND SEPARATES OUT OF A LIQUID. EX. ADDING ACID TO MILK WILL CAUSE THE PROTEIN IN MILK TO CLUMP TOGETHER.

HOW TO DETERMINE IF A CHANGE IS CHEMICAL OR PHYSICAL: – WHEN MATTER UNDERGOES A CHEMICAL CHANGE, THE COMPOSITION OF HE MATTER CHANGES; WHEN MATTER UNDERGOES A PHYSICAL CHANGE, THE COMPOSITION OF THE MATTER REMAINS THE SAME.