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Download II. Masses of Atoms
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CH. 3 - ATOMIC STRUCTURE The Atom: From Philosophical Idea to Scientific Theory OBJECTIVES • EXPLAIN THE LAW OF CONSERVATION OF MASS, THE LAW OF DEFINITE PROPORTIONS, AND THE LAW OF MULTIPLE PROPORTIONS. • SUMMARIZE THE FIVE ESSENTIAL POINTS OF DALTON’S ATOMIC THEORY. • EXPLAIN THE RELATIONSHIP BETWEEN DALTON’S ATOMIC THEORY AND THE LAW OF CONSERVATION OF MASS, THE LAW OF DEFINITE PROPORTIONS, AND THE LAW OF MULTIPLE PROPORTIONS. Chapter 3 FOUNDATIONS OF ATOMIC THEORY • THE TRANSFORMATION OF A SUBSTANCE OR SUBSTANCES INTO ONE OR MORE NEW SUBSTANCES IS KNOWN AS A CHEMICAL REACTION. • LAW OF CONSERVATION OF MASS: MASS IS NEITHER CREATED NOR DESTROYED DURING ORDINARY CHEMICAL REACTIONS OR PHYSICAL CHANGES Chapter 3 The Atom: From Philosophical Idea to Scientific Theory LAW OF CONSERVATION OF MASS Click below to watch the Visual Concept. Visual Concept Chapter 3 FOUNDATIONS OF ATOMIC THEORY, CONTINUED • LAW OF MULTIPLE PROPORTIONS: IF TWO OR MORE DIFFERENT COMPOUNDS ARE COMPOSED OF THE SAME TWO ELEMENTS, THEN THE RATIO OF THE MASSES OF THE SECOND ELEMENT COMBINED WITH A CERTAIN MASS OF THE FIRST ELEMENT IS ALWAYS A RATIO OF SMALL WHOLE NUMBERS Chapter 3 LAW OF MULTIPLE PROPORTIONS Click below to watch the Visual Concept. Visual Concept FOUNDATIONS OF ATOMIC THEORY, CONTINUED • LAW OF DEFINITE PROPORTIONS: A CHEMICAL COMPOUND CONTAINS THE SAME ELEMENTS IN EXACTLY THE SAME PROPORTIONS BY MASS REGARDLESS OF THE SIZE OF THE SAMPLE OR SOURCE OF THE COMPOUND Chapter 3 LAW OF DEFINITE PROPORTIONS Click below to watch the Visual Concept. Visual Concept Chapter 3 DALTON’S ATOMIC THEORY • ALL MATTER IS COMPOSED OF EXTREMELY SMALL PARTICLES CALLED ATOMS. • ATOMS OF A GIVEN ELEMENT ARE IDENTICAL IN SIZE, MASS, AND OTHER PROPERTIES; ATOMS OF DIFFERENT ELEMENTS DIFFER IN SIZE, MASS, AND OTHER PROPERTIES. • ATOMS CANNOT BE SUBDIVIDED, CREATED, OR DESTROYED. • ATOMS OF DIFFERENT ELEMENTS COMBINE IN SIMPLE WHOLENUMBER RATIOS TO FORM CHEMICAL COMPOUNDS. • IN CHEMICAL REACTIONS, ATOMS ARE COMBINED, SEPARATED, OR REARRANGED. Chapter 3 MODERN ATOMIC THEORY • SOME IMPORTANT CONCEPTS REMAIN UNCHANGED. • ALL MATTER IS COMPOSED OF ATOMS. • ATOMS OF ANY ONE ELEMENT DIFFER IN PROPERTIES FROM ATOMS OF ANOTHER ELEMENT. • NOT ALL ASPECTS OF DALTON’S ATOMIC THEORY HAVE PROVEN TO BE CORRECT. WE NOW KNOW THAT: • ATOMS ARE DIVISIBLE INTO EVEN SMALLER PARTICLES. • A GIVEN ELEMENT CAN HAVE ATOMS WITH DIFFERENT MASSES. Chapter 3 THE STRUCTURE OF THE ATOM • AN ATOM IS THE SMALLEST PARTICLE OF AN ELEMENT THAT RETAINS THE CHEMICAL PROPERTIES OF THAT ELEMENT. • THE NUCLEUS IS A VERY SMALL REGION LOCATED AT THE CENTER OF AN ATOM. • THE NUCLEUS IS MADE UP OF AT LEAST ONE POSITIVELY CHARGED PARTICLE CALLED A PROTON AND USUALLY ONE OR MORE NEUTRAL PARTICLES CALLED NEUTRONS. • THE NUCLEI OF ATOMS OF DIFFERENT ELEMENTS DIFFER IN THEIR NUMBER OF PROTONS • THUS, THE NUMBER OF PROTONS DETERMINES THAT ATOM’S IDENTITY. Chapter 3 FORCES IN THE NUCLEUS • WHEN TWO PROTONS ARE EXTREMELY CLOSE TO EACH OTHER, THERE IS A STRONG ATTRACTION BETWEEN THEM. • A SIMILAR ATTRACTION EXISTS WHEN NEUTRONS ARE VERY CLOSE TO EACH OTHER OR WHEN PROTONS AND NEUTRONS ARE VERY CLOSE TOGETHER. • THE SHORT-RANGE PROTON-NEUTRON, PROTON-PROTON, AND NEUTRON-NEUTRON FORCES THAT HOLD THE NUCLEAR PARTICLES TOGETHER ARE REFERRED TO AS NUCLEAR FORCES. Chapter 3 THE STRUCTURE OF THE ATOM, CONTINUED • SURROUNDING THE NUCLEUS IS A REGION OCCUPIED BY NEGATIVELY CHARGED PARTICLES CALLED ELECTRONS • PROTONS, NEUTRONS, AND ELECTRONS ARE OFTEN REFERRED • Atoms are electrically neutral because they contain equal TO AS SUBATOMIC PARTICLES. numbers of protons and electrons. • MOST OF THE ATOM IS EMPTY Chapter 3 PROPERTIES OF SUBATOMIC PARTICLES Chapter 3 THE SIZES OF ATOMS • THE RADIUS OF AN ATOM IS THE DISTANCE FROM THE CENTER OF THE NUCLEUS TO THE OUTER PORTION OF ITS ELECTRON CLOUD. • BECAUSE ATOMIC RADII ARE SO SMALL, THEY ARE EXPRESSED USING A UNIT THAT IS MORE CONVENIENT FOR THE SIZES OF ATOMS. • THIS UNIT IS THE PICOMETER, PM. • WHAT IS THE CHARGE OF A NEUTRON? • MOST OF AN ATOM IS ___________ • WHERE ARE ELECTRONS FOUND? • WHAT IS THE NUCLEUS OF AN ATOM MADE UP OF? • A MOLECULE OF CARBON MONOXIDE, CO, HAS ONE ATOM OF OXYGEN WHILE A MOLECULE OF CARBON DIOXIDE, CO2, HAS TWO. IN A SAMPLE OF CO CONTAINING 1 G OF CARBON, 1.33 G OF OXYGEN WILL COMBINE WITH THE CARBON TO FORM THE MOLECULE. WHAT IS THE MASS OF OXYGEN IN A SAMPLE OF CO2 CONTAINING 1 G OF CARBON? A.1.33 G C.2.66 G B.3.0 G D.0.0 G Chapter 3 ATOMIC NUMBER • ATOMS OF DIFFERENT ELEMENTS HAVE DIFFERENT NUMBERS OF PROTONS. • ATOMS OF THE SAME ELEMENT ALL HAVE THE SAME NUMBER OF PROTONS. • THE ATOMIC NUMBER OF AN ELEMENT IS THE NUMBER OF PROTONS OF EACH ATOM OF THAT ELEMENT. MASS NUMBER • MASS # = PROTONS + NEUTRONS always a whole number NOT on the Periodic Table! Publishing Company, Inc. ISOTOPES • ATOMS OF THE SAME ELEMENT WITH DIFFERENT MASS NUMBERS. Nuclear symbol: Mass # Atomic # Hyphen notation: carbon-12 12 6 C ISOTOPES C. Johannesson © Addison-Wesley Publishing Company, Inc. ISOTOPES • CHLORINE-37 • ATOMIC #: 17 • MASS #: 37 • # OF PROTONS: 17 • # OF ELECTRONS: 17 • # OF NEUTRONS: 20 37 17 Cl AVERAGE ATOMIC MASS • WEIGHTED AVERAGE OF ALL ISOTOPES • ON THE PERIODIC TABLE • ROUND TO 2 DECIMAL PLACES Avg. Atomic Mass (mass)(% ) (mass )(% ) 100 AVERAGE ATOMIC MASS • EX: CALCULATE THE AVG. ATOMIC MASS OF OXYGEN IF ITS ABUNDANCE IN NATURE IS 99.76% 16O, 0.04% 17O, AND 0.20% 18O. Avg. (16)(99.76 ) (17)(0.04) (18)(0.20) 16.00 Atomic 100 amu Mass AVERAGE ATOMIC MASS • EX: FIND CHLORINE’S AVERAGE ATOMIC MASS IF APPROXIMATELY 8 OF EVERY 10 ATOMS ARE CHLORINE-35 AND 2 ARE CHLORINE-37. Avg. Atomic Mass (35)(8) (37)(2) 35.40 amu 10 CH 3- THE MOLE COUNTING ATOMS WHAT IS THE MOLE? • A COUNTING NUMBER (LIKE A DOZEN) DESCRIBES THE NUMBER OF PARTICLES • AVOGADRO’S NUMBER (NA) • 1 MOL = 6.02 1023 ITEMS A large amount!!!! n 1 mole of hockey pucks would equal the mass of the moon! n 1 mole of basketballs would fill a bag the size of the earth! • 1 MOLE OF PENNIES WOULD COVER THE EARTH 1/4 MILE DEEP! Chapter 3 THE MOLE Click below to watch the Visual Concept. Visual Concept MOLAR MASS • MASS OF 1 MOLE OF AN ELEMENT OR COMPOUND. - MOLAR MASS • EQUAL TO ATOMIC MASS UNITS PER ATOM (AMU) FOUND ON PERIODIC TABLE • WRITTEN IN UNITS GRAMS PER MOLE (G/MOL) MOLAR MASS EXAMPLES • CARBON 12.01 g/mol • ALUMINUM 26.98 g/mol • ZINC 65.39 g/mol MOLAR MASS EXAMPLES • WATER H2O 2(1.01) + 16.00 = 18.02 g/mol • SODIUM CHLORIDE NaCl 22.99 + 35.45 = 58.44 g/mol MOLAR MASS EXAMPLES • SODIUM BICARBONATE NaHCO3 22.99 + 1.01 + 12.01 + 3(16.00) = 84.01 g/mol • SUCROSE C12H22O11 12(12.01) + 22(1.01) + 11(16.00) = 342.34 g/mol Chapter 3 AVOGADRO’S NUMBER Click below to watch the Visual Concept. Visual Concept MOLAR CONVERSIONS molar mass 6.02 1023 MASS NUMBER MOLES IN GRAMS OF Atoms/molecule s (g/mol) (atoms/mol) Chapter 3 SOLVING MOLE PROBLEMS MOLAR CONVERSION EXAMPLES • HOW MANY MOLES OF CARBON ARE IN 26 G OF CARBON? 26 g C 1 mol C 12.01 g C = 2.2 mol C Chapter 3 MOLAR CONVERSION EXAMPLES •WHAT IS THE MASS IN GRAMS OF 3.50 MOL OF THE ELEMENT COPPER, CU? Chapter 3 •THE MOLAR MASS OF COPPER FROM THE PERIODIC TABLE IS ROUNDED TO 63.55 G/MOL. MOLAR CONVERSION EXAMPLES • HOW MANY GRAMS OF CARBON ARE IN 4.0 MOLES OF CARBON? 4.0 mol C 12.01 g C = 48 g C 1 mol C MOLAR CONVERSION EXAMPLES • HOW MANY MOLECULES ARE IN 2.50 MOLES OF C12H22O11? 6.02 1023 2.50 mol molecules 1 mol = 1.51 1024 molecules C12H22O11 MOLAR CONVERSION EXAMPLES • FIND THE MASS OF 2.1 1024 MOLECULES OF NAHCO3. 2.1 1024 84.01 g molecules 1 mol 6.02 1023 1 mol molecules = 290 g NaHCO3