CH. 3 - ATOMIC STRUCTURE

The Atom: From Philosophical Idea to Scientific TheoryOBJECTIVES

•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.

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

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Chapter 3The Atom: From Philosophical Idea to Scientific Theory

LAW OF CONSERVATION OF MASS

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

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Chapter 3

LAW OF MULTIPLE PROPORTIONS

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

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Chapter 3

LAW OF DEFINITE PROPORTIONS

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 WHOLE-NUMBER 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.

Chapter 3

• THE NUCLEI OF ATOMS OF DIFFERENT ELEMENTS DIFFER IN THEIR NUMBER OF PROTONS

• THUS, THE NUMBER OF PROTONS DETERMINES THAT ATOM’S IDENTITY.

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 TO AS SUBATOMIC PARTICLES.

• MOST OF THE ATOM IS EMPTY

Chapter 3

• Atoms are electrically neutral because they contain equal numbers of protons and electrons.

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.

Chapter 3

• 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 B.3.0 GC.2.66 G D.0.0 G

Review ????Review ????

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.

Chapter 3

MASS NUMBER

• MASS # = PROTONS + NEUTRONS

always a whole number

NOT on the Periodic Table!

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ISOTOPES

• ATOMS OF THE SAME ELEMENT WITH DIFFERENT MASS NUMBERS.

C126Mass #

Atomic #

Nuclear symbol:

Hyphen notation: carbon-12

ISOTOPES

C. Johannesson

© Addison-Wesley Publishing Company, Inc.

ISOTOPES

• CHLORINE-37

• ATOMIC #:

• MASS #:

• # OF PROTONS:

• # OF

ELECTRONS:

• # OF NEUTRONS:

17

37

17

17

20

Cl3717

AVERAGE ATOMIC MASS

• WEIGHTED AVERAGE OF ALL ISOTOPES

• ON THE PERIODIC TABLE

• ROUND TO 2 DECIMAL PLACES

100

(%)(mass(mass)(%) )

Avg.AtomicMass

Avg.AtomicMass

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.

100

(18)(0.20)(17)(0.04))(16)(99.76 16.00amu

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.AtomicMass

10

(37)(2)(35)(8)35.40 amu

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!!!!

1 mole of hockey pucks would equal the mass of the moon!

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!

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Chapter 3

THE MOLE

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

• ALUMINUM

• ZINC

12.01 g/mol

26.98 g/mol

65.39 g/mol

MOLAR MASS EXAMPLES• WATER

• SODIUM CHLORIDE

H2O

2(1.01) + 16.00 = 18.02 g/mol

NaCl

22.99 + 35.45 = 58.44 g/mol

MOLAR MASS EXAMPLES

• SODIUM BICARBONATE

• SUCROSE

NaHCO3

22.99 + 1.01 + 12.01 + 3(16.00)

= 84.01 g/mol

C12H22O11

12(12.01) + 22(1.01) + 11(16.00)

= 342.34 g/mol

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Chapter 3

AVOGADRO’S NUMBER

MOLAR CONVERSIONS

molar mass

(g/mol)

MASS

IN

GRAMS

MOLESNUMBER

OF

Atoms/molecules

6.02 1023

(atoms/mol)

SOLVING MOLE PROBLEMSChapter 3

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

•WHAT IS THE MASS IN GRAMS OF 3.50 MOL OF THE ELEMENT COPPER, CU?

Chapter 3MOLAR CONVERSION EXAMPLES

•THE MOLAR MASS OF COPPER FROM THE PERIODIC TABLE IS ROUNDED TO 63.55 G/MOL.

Chapter 3

MOLAR CONVERSION EXAMPLES

•HOW MANY GRAMS OF CARBON ARE IN 4.0 MOLES OF CARBON?

4.0 mol C 12.01 g C

1 mol C= 48 g C

MOLAR CONVERSION EXAMPLES

•HOW MANY MOLECULES ARE

IN 2.50 MOLES OF C12H22O11?

2.50 mol6.02 1023

molecules

1 mol

= 1.51 1024

molecules C12H22O11

MOLAR CONVERSION EXAMPLES

•FIND THE MASS OF 2.1 1024

MOLECULES OF NAHCO3.

2.1 1024

molecules 1 mol

6.02 1023

molecules

= 290 g NaHCO3

84.01 g

1 mol