Chapter 2 (Part I)Chapter 2 (Part I)

Atoms, Molecules, and Ions Atoms, Molecules, and Ions

HistoryHistory GreeksGreeks Democritus and Leucippus - atomosDemocritus and Leucippus - atomos Aristotle- elementsAristotle- elements AlchemyAlchemy 1660 - Robert Boyle- experimental 1660 - Robert Boyle- experimental

definition of element.definition of element. Lavoisier- Father of modern chemistryLavoisier- Father of modern chemistry He wrote the book- used measurementHe wrote the book- used measurement

LawsLaws Conservation of MassConservation of Mass Law of Definite Proportion-Law of Definite Proportion- compounds compounds

have a constant composition by mass.have a constant composition by mass. They react in specific ratios by mass.They react in specific ratios by mass. Multiple Proportions-Multiple Proportions- When two elements When two elements

form more than one compound, the ratios of form more than one compound, the ratios of the masses of the second element that the masses of the second element that combine with one gram of the first can be combine with one gram of the first can be reduced to small whole numbers.reduced to small whole numbers.

What?!What?! Water has 8 g of oxygen per g of hydrogen.Water has 8 g of oxygen per g of hydrogen. Hydrogen peroxide has 16 g of oxygen per Hydrogen peroxide has 16 g of oxygen per

g of hydrogen.g of hydrogen. 16/8 = 2/116/8 = 2/1 Small whole number ratiosSmall whole number ratios

Example of Law Of Multiple Example of Law Of Multiple ProportionsProportions

Mercury has two oxides. One is 96.2 % Mercury has two oxides. One is 96.2 % mercury by mass, the other is 92.6 % mercury by mass, the other is 92.6 % mercury by mass.mercury by mass.

Show that these compounds follow the law Show that these compounds follow the law of multiple proportion.of multiple proportion.

Speculate on the formula of the two oxides.Speculate on the formula of the two oxides.

Your TurnYour Turn Nitrogen and oxygen form two compounds.Nitrogen and oxygen form two compounds.

Show that they follow the law of multiple Show that they follow the law of multiple proportionsproportions

Amount NAmount N Amount OAmount O

Compound ACompound A 1.206 g1.206 g 2.755 g2.755 g

Compound BCompound B 1.651g1.651g 4.714 g4.714 g

Dalton’s Atomic TheoryDalton’s Atomic Theory 1. Elements are made up of atoms1. Elements are made up of atoms 2. Atoms of each element are identical. 2. Atoms of each element are identical.

Atoms of different elements are different.Atoms of different elements are different. 3. Compounds are formed when atoms 3. Compounds are formed when atoms

combine. Each compound has a specific combine. Each compound has a specific number and kinds of atom.number and kinds of atom.

4. Chemical reactions are rearrangement of 4. Chemical reactions are rearrangement of atoms. Atoms are not created or destroyed.atoms. Atoms are not created or destroyed.

Gay-Lussac- under the same conditions of Gay-Lussac- under the same conditions of temperature and pressure, compounds temperature and pressure, compounds always react in whole number ratios by always react in whole number ratios by volume.volume.

Avagadro- interpreted that to mean Avagadro- interpreted that to mean at the same temperature and pressure, equal at the same temperature and pressure, equal

volumes of gas contain the same number of volumes of gas contain the same number of particlesparticles

(called Avagadro’s hypothesis)(called Avagadro’s hypothesis)

A Helpful ObservationA Helpful Observation

Experiments to determine what Experiments to determine what an atom wasan atom was

J. J. Thomson- used Cathode ray tubesJ. J. Thomson- used Cathode ray tubes

Thomson’s ExperimentThomson’s Experiment

Voltage source

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Thomson’s ExperimentThomson’s Experiment

Voltage source

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Thomson’s ExperimentThomson’s Experiment

Voltage source

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Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field he found that the By adding an electric field he found that the moving pieces were negative moving pieces were negative

+

-

Thomsom’s ModelThomsom’s Model Found the electronFound the electron Couldn’t find Couldn’t find

positive (for a while) positive (for a while) Said the atom was Said the atom was

like plum puddinglike plum pudding A bunch of positive A bunch of positive

stuff, with the stuff, with the electrons able to be electrons able to be removed removed

Millikan’s ExperimentMillikan’s Experiment

Atomizer

Microscope

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Oil

Millikan’s ExperimentMillikan’s Experiment

Oil

Atomizer

Microscope

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Oil droplets

Millikan’s ExperimentMillikan’s Experiment

X-rays

X-rays give some drops a charge by knocking offelectrons

Millikan’s ExperimentMillikan’s Experiment

+

Millikan’s ExperimentMillikan’s Experiment

They put an electric charge on the plates

++

--

Millikan’s ExperimentMillikan’s Experiment

Some drops would hover

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--

Millikan’s ExperimentMillikan’s Experiment

+

+ + + + + + +

- - - - - - -

Millikan’s ExperimentMillikan’s Experiment

Measure the drop and find volume from 4/3πr3

Find mass from M = D x V

++

--

Millikan’s ExperimentMillikan’s Experiment

From the mass of the drop and the charge on the plates, he calculated the charge on an electron

++

--

RadioactivityRadioactivity Discovered by accidentDiscovered by accident BequerelBequerel Three types Three types

– alpha- helium nucleus (+2 charge, large alpha- helium nucleus (+2 charge, large mass)mass)

– beta- high speed electronbeta- high speed electron

– gamma- high energy lightgamma- high energy light

Rutherford’s ExperimentRutherford’s Experiment Used uranium to produce alpha particlesUsed uranium to produce alpha particles Aimed alpha particles at gold foil by Aimed alpha particles at gold foil by

drilling hole in lead blockdrilling hole in lead block Since the mass is evenly distributed in Since the mass is evenly distributed in

gold atoms alpha particles should go gold atoms alpha particles should go straight through.straight through.

Used gold foil because it could be made Used gold foil because it could be made atoms thinatoms thin

Lead block

Uranium

Gold Foil

Florescent Screen

What he expected

Because

Because, he thought the mass was evenly distributed in the atom

What he got

How he explained it

+

Atom is mostly emptyAtom is mostly empty Small dense,Small dense,

positive piecepositive piece at centerat center

Alpha particles Alpha particles are deflected byare deflected by it if it if they get closethey get close enough enough

+

Modern ViewModern View The atom is mostly The atom is mostly

empty spaceempty space Two regionsTwo regions Nucleus- protons and Nucleus- protons and

neutronsneutrons Electron cloud- region Electron cloud- region

where you have a where you have a chance of finding an chance of finding an electronelectron

Sub-atomic ParticlesSub-atomic Particles Z - atomic number = number of protons Z - atomic number = number of protons

determines type of atomdetermines type of atom A - mass number = number of protons + A - mass number = number of protons +

neutronsneutrons Number of protons = number of electrons if Number of protons = number of electrons if

neutralneutral

SymbolsSymbols

XA

Z

Na23

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