is 240: discovering the atom dr. dean johnston department of chemistry and biochemistry dr. david...

IS 240: Discovering the Atom

Dr. Dean Johnston

Department of Chemistry and Biochemistry

Dr. David Robertson

Department of Physics and Astronomy

Course Overview

• Science as a “way of knowing”• Focus on the atomic structure of matter

– How do we know about it?

– What does it tell us?

– Is there anything inside them?

• A multi-disciplinary perspective – chemistry and physics

• Includes laboratory exercises• Builds a foundation for later IS science courses

Course Structure

• Periodically split into two groups (A and B) for lab work in parallel tracks lasting two weeks

• Each split session involves one chemistry and one physics lab

• Each group spends one week at each, swapping in between

• “Joint” sessions glue things together

Course Materials

• Text: The Last Sorcerers: The Path From Alchemy to the Periodic Table, by Richard Morris

• Other readings provided as handouts or on line• Course web page:

http://www.otterbein.edu/home/fac/dvdgrbrt/is240/– Notices, lecture notes, the syllabus, online resources, grades,

and more…

• On reserve at the library:– The Blair Handbook– The Everyday Writer

http://www.otterbein.edu/home/fac/dvdgrbrt/is240/

Modes of Inquiry• “Ways of knowing” – ways to ask (and answer)

questions– Are there regularities in the natural world? If so, what are they?

– What are the basic things that exist in the world?

– Was there a creator?

– What is the nature of good and evil?

– Is there such a thing as beauty?

– How can human societies best be organized?

• Different modes may be more or less appropriate for different questions

• Most people use all of them

Philosophical

• Study of the ultimate reality, causes, and principles underlying being and thinking

• Esthetics, ethics, politics, metaphysics, logic, epistemology (nature and origin of knowledge)

• A search for wisdom based on logic and principle• May be based in part on observation, though often

speculative

Philosophy is a hypothetical interpretation of the unknown, or of the inexactly known. It is the front trench in the siege of truth, while science is the captured territory.

–Will Durant

Theological• Knowledge is revealed, through

– Scriptures

– Personal revelations, prayer

– Contemplation and interpretation of mystics

• Modern religious interpretations focus mainly on ethical questions– How should you live your life?

– What are right and wrong?

• Historically, theology has not always considered science to be a valid way of knowing

Scientific

• Conclusions based on systematic observation and manipulation of the natural world

• Only deals with the natural world!– Excludes the “supernatural” by definition

• Systematized by Bacon, Descartes and Galileo in the 17th century

• Aims to give conclusionsthat are independent of theindividual

The task of science is both to extend the range of our experience and to reduce it to order.

–Niels Bohr

The Scientific “Method”

The whole of science is nothing more than a refinement of everyday thinking.

–Albert Einstein

A Classical Example

• Aristotle observes that during lunar eclipses the Earth’s shadow on the moon is curved

A Lunar Eclipse

A Classical Example, cont.

• He assumes it will be curved for all eclipses

• A hypothesis that explains this: the earth is round

• A prediction of this hypothesis is that the location of the stars in the sky should be different for observers at different latitudes

• This is confirmed by additional observations– E.g. Canopus is visible in Egypt but not further north

Local Sky

• Depending on your location you see completely different stars!

N

North Pole

South Pole

Polaris

Solar Eclipse

• Umbra – region of total shadow

• Penumbra – region of partial shadow

Observations

• Scientific Fact (AAAS): An observation that has been repeatedly confirmed

• Examples:– The sky is blue

– Humans have 46 chromosomes in somatic cells under normal conditions

– The sun rises in the east and sets in the west

• Always subject to reconsideration (in principle) but in practice assumed to be true

• Some are better established than others– At the “cutting edge” the facts may not be so clear (yet)

Experimental vs. Historical Observations

• Experimental– Tests/observations can be repeated with different conditions

– Hypotheses can be refined after further testing

– Physics, chemistry, molecular biology, etc.

• Historical– Evidence that something happened in the past

– Reconstruction of the past

– Forensic science, geology, paleontology, cosmology, much of biology, etc.

• Different sciences rely to different degrees on the two kinds of observations

Scientific Theories

• The word “theory” connotes “uncertainty” to non-scientists, but this is incorrect in the scientific context

• AAAS Definition: “A well substantiated explanation of some aspect of the physical world”

• The highest rank of scientific explanation!– Not “just” a theory

• Substitute “body of knowledge known as...” for “theory of...” (e.g., “body of knowledge known as relativity” rather than “theory of relativity”)

• Use “hypothesis” for an untested idea

What is the aim of (experimental) science?

• A search for order or patterns in nature– The “scientific method” sets out the rules for the search

• In physics and chemistry these patterns are generally expressed mathematically– E.g. for falling bodies, d is proportional to t2

– Water is composed of hydrogen and oxygen in a mass ratio of 1:8

• (At least) two amazing facts:– That such patterns exist at all!

– That so much can be explained by so few basic ideas (patterns)

• Much of the history of science has involved the search for ever more general, all-encompassing patterns in nature

Johannes Kepler (1571–1630)

• Key question: How are things happening?

• Major Works:– Harmonices Mundi (1619)

– Rudolphian Tables (1612)

– Astronomia Nova

– Dioptrice

Kepler’s Beginnings

• Astrologer and mystic

• Tried to find “music in the heavens”

• Attempted to explain distances to the five known planets by nested spheres resting on the five “Platonic” solids

• Pre-scientific

Johannes Kepler

Manuscript: trying to disentangleThe mystery of Mars’ orbit

Kepler’s First LawThe orbits of the planets are ellipses, with the Sun at one “focus”

Kepler’s Second LawAn imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal times

Kepler’s Third Law

The square of a planet’s orbital period is (in appropriate units) equal to the cube of its orbital semi-major axis: P2 = a3

Planet Orbital Semi-Major Axis Orbital Period P2/a3

(au) (Earth years)Mercury 0.387 0.241 1.002Venus 0.723 0.615 1.001Earth 1.000 1.000 1.000Mars 1.524 1.881 1.000Jupiter 5.203 11.86 0.999Saturn 9.539 29.46 1.000Uranus 19.19 84.01 0.999Neptune 30.06 164.8 1.000Pluto 39.53 248.6 1.001

Isaac Newton (1642–1727)

• Key question: Why are things happening?

• Invented calculus and physics while on “vacation” from college

• His three Laws of Motion, together with the Law of Universal Gravitation, explain the motion of planets and of objects on Earth (and more!)

• Later in life he was Master of the Mint, dabbled in alchemy, and spent a great deal of effort trying to make his personal enemies miserable

Newton’s Laws of Motion

A general framework for describing any motion

1. Every body continues in a state of rest or in a state of uniform motion in a straight line unless it is compelled to change that state by forces acting on it (Law of Inertia)

2. The change of motion (acceleration) is proportional to the force applied (F = ma where m is the mass of the object)

3. For every action (force), there is an equal and opposite reaction

Law of Universal Gravitation

MEarth Mman

R

2Earth ManGM M

FR

Orbital Motion

Cannon “Thought Experiment”

The Unity of Nature

• Newton showed that the orbital motion of planets reflects the same pattern in nature as does motion on Earth (balls rolling down planes, cannonballs, falling apples, etc.)

• Also explained the ocean tides– Due to gravitational attraction of the moon

• Many apparently different phenomena are thus related!

• Later, Einstein showed that Newton’s Laws are an approximation to an even deeper, more subtle pattern

• That new pattern incorporates everything Newton does, plus more – including the structure of the universe itself!

Scientific Theories

• Must be falsifiable (Karl Popper)– There must be some way the theory could fail

– Appeals to, e.g., supernatural influences are not allowed!

• Should make predictions– The more, the better!

• Theories that are very well tested and have the widest applicability are often known as “laws of nature”

• Always subject to revision or modification, though

• Occam’s Razor: simpler is usually better!

Experiments

• Experiments must be repeatable – Others must be able to duplicate your results!

• Possible outcomes of an experiment:– The experiment may support the theory

• We then continue to make predictions and test them

– The experiment may falsify the theory• We need a new theory that describes both the original data and the

results of the new experiment

• Since we cannot do every possible experiment, a theory can never be proven true; it can only be proven false

The aim of science is not to open the door to everlasting wisdom, but to set a limit on everlasting error.

–Bertolt Brecht, in The Life of Galileo

Other Characteristics

• Science is cumulative and progressive– The new absorbs the old

– Successful theories are never “merely” wrong, even when overthrown

• They are usually seen to be approximations of the new, deeper principle

• Science is self-correcting– Scientific work is open – scientists make their work available to

others so that they may test it

– Outright fraud is rare, and (usually) quickly detected

– Mistakes are uncovered by independent checks

“Science is the systematic enterprise of gathering knowledge about the world and organizing and condensing that knowledge into testable laws and theories.

[American Association of Physics Teachers, Am. J. Phys. 67 (8), p. 659 (1999)]

Summary

“The success and credibility of science is anchored in the willingness of scientists to:

1. expose their ideas and results to independent testing and replication by other scientists; this requires the complete and open exchange of data, procedures and materials;

2. abandon or modify accepted conclusions when confronted with more complete or reliable experimental evidence.

Adherence to these principles provides a mechanism for self-correction that is the foundation of the credibility of science.”

The Domain of Science

• Science deals with natural phenomena, and only allows natural explanations– Remember, theories must be falsifiable!

• Some questions are not answerable in this way– Is there life after death?

– Do we have souls?

– Is abortion wrong?

– Should capital punishment be allowed?

– What is the best form of government?

– …

• However, science may provide input for these questions, e.g. by predicting consequences

Science and Religion

• Often seen as being in conflict– Copernicus vs Ptolemey; Galileo

– Evolution

• Whether or not there is a conflict, and if so what it entails, is a philosophical judgment that each person must make– Many scientists are religious

– Many churches accept scientific findings

– The converses are true also!

“Same World” Model

• Science and Religion deal in principle with the same subjects

• Conflicts are hard to resolve since science cannot accept evidence on faith and religion need not accept scientific explanations– Example: What is the age of the Earth?

• Usually results in a claim that one is right and the other wrong– Fundamentalists

– Some scientists who see religion as unnecessary and regressive

“Separate World” Model

• Science and Religion deal in principle with different subjects

• Therefore no overlap or conflict; can co-exist peacefully– Science deals with the natural world

– Religion deals with the spiritual world, ethics

– There may be conflict in a few areas, which vary from person to person

• The position of many churches and scientists

Measurements: The Metric System

• Units of length: – The meter (m) 3 ft. 4 in.

– The kilometer (km) = 1000 m or about 0.6 mi.

• Units of mass:– The kilogram (kg). 1 kg weighs about 2.2 lbs. (The lb. is a unit

of weight)

• Units of time: – The second, same as in the English system

Scientific Notation• 108 means multiply by 10 eight times

– 108 is 1 followed by 8 zeroes

– Example: 1.5 108 km = 1.5 100,000,000 = 150,000,000 km

– 100 is a 1 followed by no zeroes, i.e. just 1

• A negative exponent means divide instead of multiply:– 10–6 means divide by 10 six times

– Example: 2 10–6 m = 2/1,000,000 = 0.000002 m

• To multiply numbers, add exponents:– Example: 104 1023 = 104 + 23 = 1027

• To divide, subtract exponents:– Example: 104 / 1023 = 104 – 23 = 10–19

– Note: 1 / 104 = 100 / 104 = 10–4

Exercises

• Evaluate the following:1. 102 1017

2. 100 10–4

3. 102/108

4. (1.5 103) (2 1023)

= 1019

= 10–4

= 10–6

= 3 1026

“Fermi Problems”

• (Very!) rough estimation

• Looking basically for the right power of 10 in the answer– Is the answer more like 10 or 100 or 1000…?

– Round off, drop fractions, estimate needed information to the nearest power of 10

• No single “right” answer; only more or less reasonable ones

• The Classic: How many piano tuners are there in Chicago?

Example

• How long would it take a person to run from New York to LA? (A week? A year? Several years?)– Assume good runner: maybe 6 mph for 5 hours a day

– Hence about 30 miles per day• Probably too optimistic, but in the right ballpark

– Distance from NY to LA about 3000 miles, so

T = (3000 mi)/(30 mi/day)

or about 100 days

• If another person arrived at 123.45 days, that’s fine – it has the same “order of magnitude” (power of 10)

• Need to know some basic quantitative facts about the world

Problems

1. About how many pizzas are consumed in the US each day?

• Say 300 million people in the US (3 108)

• Maybe 2/3 of these eat pizza regularly (2 108)

• Say these people eat half a pizza every three weeks– Likely more for students , less for some others

• So every three weeks about 1 108 pizzas are eaten

• About 1 108 /20 = 1 108 5 10–2 = 5 106 per day

Problems

1. Estimate the total amount of human blood in the world. If Lake Erie were emptied of water and filled with this blood, about how deep would it be?

• Say 6 billion people in the world (6 109)

• Say each has about 5 pints of blood on average (30 109

pints total)

• A pint is half a quart, or about 30 cubic inches

• Assume Lake Erie a rectangle about 200 mi by 80 mi– Surface area about 6 1013 square inches

• Depth = (volume of blood)/(area) would be about (30 109 30)/ 6 1013 = 30 5 10–4 = 1.5 10–2 inches

The probability that a woman of age 40 has breast cancer is about 1%. If she has breast cancer, the probability that she tests positive on a screening mammogram is 90%. If she does not have breast cancer, the probability that she nevertheless tests positive is 9%. What are the chances that a woman who tests positive actually has breast cancer?

Powers of Ten – From Man to Universe –

100 meters

=1 meter

The Human

Scale


101 meters

=10 meters

Pond with

lilly pads


102 meters

=100 meters

Japanese Tea

Garden


103 meters = 1000 m= 1 km

Golden GatePark


104 meters

=10 km

San Francisco


105 meters

=100 km

SF Bay area


106 meters

=1000 km

California


107 meters

=10,000 km

North and

Central America


108 meters

=100,000 km

Earth in

Space


109 meters

=1,000,000 km

Earth and

Moon


1010 meters

Part of Earth’s

Orbit around

the Sun


1011 meters

1 A.U.(an “Astronomical Unit”)

Venus, Earth

and Mars


1012 meters

Orbit of

Jupiter


1013 meters

The Solar

System


1014 meters

Solar System

in Space


1015 meters

The Sun -

“a bright star”


1016 meters

1 lyr(light year)

The Sun -

“just another star”


1017 m

10 lyr

The Nearest

Stars


1018 m =

100 lyr

Stars within

50 lyr


1019 m =

1,000 lyr

A cloud of Stars- making up constellations


1020 m

10,000 lyr

Spiral Arm of

the Milky Way


1021 m

100,000 lyr

The Milky Way

– Our Galaxy


1022 m

1,000,000 lyr

The Local

Group


1023 m

10 x 106 lyr

The Virgo

Cluster


1024 m

= 108 lyr

Clusters

of Galaxies


1025 m 109 lyr

The ObservableUniverse:Many clusters of galaxies – and even more empty space


100 meters

=1 meter

The Human

Scale


10–1 m

= 0.1 m

Lilly and bee


10–2 m

= 0.01 m

Bee’s head


10–3 m

=1 mm

=1 millimeter

A bee’s eye


10–4 m

= 0.0001 m

=100 micrometers

Pollen grain


10–5 m

= 0.00001 m

= 10 m

Bacteria


10–6 m

= 1 m

Virus on a

Bacterium


10–7 m = 0.1 m= 100 nanometers= 100 nm

A virus


10–8 m

= 10 nm

DNA in a virus


10–9 m

= 1 nm

Molecules of

DNA


10–10 m = 1 Angstrom= 1 Å

Carbon’s outerelectron shell


10–11 m = 10 picometers= 10 pm

The inner electron cloud


10–12 m = 1 picometer= 1 pm

Within the electron cloud


10–13 m

=100 femtometers

=100 fm

The nucleus


10–14 m

= 10 fm

Carbon nucleus


10–15 m

= 1 fm

Inside the

proton


10–16 m

= 100 attometers

= 100 am

Quarks and gluons

A Short History of Atomic Ideas

• Earliest formulation of the idea due to the Greeks– “atom” = a-tom, Greek for “not divisible”

– Pre-scientific, i.e. no scientific reason for believing it!

• In Rome: Epicurus and Lucretius (95 to 55 B.C.)

• Out of favor (along with much other learning and scholarship) for almost 2000 years

• 18th century: Re-introduced by Daniel Bernoulli, Roger Boscovitch

• Dalton discovers Laws of Definite and Multiple Proportions– Rules for combining elements to make compounds

• Kinetic Theory (Clausius, Maxwell, Boltzmann; 19th century)– Description of matter in terms of randomly moving particles (atoms)

• Brownian Motion (Brown, Einstein; early 20th century)

Democritus (~460–380 B.C.)

• Lived in northern Greece• Thought experiment: Subdivide a piece of gold

– Each part is still gold after every division– Can you subdivide for ever?– Claimed there must be some limit; matter is made of particles that

cannot be further divided

• These “atoms” move endlessly in all directions in “the void”

• Also: smelling bread from a distance– Particles from the bread must break off and travel to our noses

• Determinism?– A relief from capricious and cruel gods

Lucretius (~95–55 B.C.)

• Roman philosopher and poet; student of Epicurus

• Manuscript De Rerum Natura (On the Nature of Things) re-discovered in late 14th century

• Contemporary of Julius Caesar; beginning of Rome’s decline

• Allegedly driven mad by a “love potion” given to him by his wife, and committed suicide

• Atheistic and deterministic

Lucretius…clothes hang above a surf swept shoregrow damp; spread them in the sun they dry again.Yet it is not apparent to us howthe moisture clings to the cloth, or flees the heat.Water, then, is dispersed in particles,atoms too small to be observable.…For surely the atoms did not hold council, assigningorder to each, flexing their keen minds with questions of place and motion and who goes where.But shuffled and jumbled in many ways, in the courseof endless time they are buffeted, driven along,chancing upon all motions, combinations.At last they fall into such an arrangementas would create this universe…

–Lucretius, De Rerum Natura

Early Objections

• Some quasi-religious or philosophical, of course, but some “scientific” ones as well

• How can atoms continue moving for all time without stopping?– According to Aristotle, moving objects come to a halt unless

something intervenes to keep them moving

• The “void” in which atoms supposedly move cannot exist, according to some philosophers:– For anything to exist it must have a name, which refers to

something rather than nothing

– Since “nothing” cannot have such a name, it therefore cannot exist

The Medieval Setting

• Dominant church

• ~ 1000 years of relative stagnation in the west

• Experimental research greatly reduced

• To answer a question:

“Study the Bible or Aristotle!”

The Renaissance Setting

• Invention of the printing press (1450) by Gutenberg– Books become widely available!

• End of the Church’s domination in the Middle Ages

• Back to the roots (renaissance means “rebirth”)

• Intellectual movement

The Baroque Setting

• Counter-reformation in the 1600s; church much stricter

• G. BRUNO (Italian; 1548) proposes that the Sun is just one of an infinite number of stars; burned at the stake for heresy (1600)

• 30 Years War (1618-1648) between religions

• Many new inventions: telescope, air pump, etc.

Dalton

Modern Terminology

• Most substances can be chemically decomposed into other substances– E.g. water can be decomposed into hydrogen and oxygen

• Substances that cannot be decomposed are called elements

• An “atom” is the smallest indivisible unit of an element

• A “molecule” is a group of atoms stuck together – The smallest unit of a compound

• In some cases where it doesn’t matter, we may speak of a particle, which might actually be an atom or molecule

What is Heat?

• A central part of the mystery• Majority view around 1800: heat is a fluid, called caloric• It flows from hotter bodies to colder ones

– E.g. we drop a hot horseshoe in water; caloric flows from the shoe into the water, cooling the shoe and heating the water

• Mysterious, undetectable (?)• In the atomic theory, heat has to do with the (random)

motion of the particles– Faster speeds on average means higher temperature

• Rudolf Clausius: The Kind of Motion We Call Heat (1857)• A consequence: There is a lowest temperature! (Davy)

Kinetic Theory

• A description of matter in terms of randomly moving particles (atoms)

• Response to Aristotle (how can atoms stay moving forever?) given by Newton

• For a gas, for example– Pressure is due to the particles

colliding with the container walls

– Temperature (warmth) is a measure of the average speed of the particles

Ludwig Boltzmann (1844–1906)• Professor in Vienna

– Also Graz, Munich, Heidelberg, Berlin, Leipzig

• Brings kinetic theory on a firm foundation – “statistical mechanics”– Independently: J. W. Gibbs

• Ongoing battles with Ernst Mach and others over atomic and kinetic theory

• Moody, depressed, highly sensitive to criticism

• Suicide (perhaps) due to despair at lack of acceptance of his ideas

The Conflict With Mach

• Mach’s view: “Positivism” (a particularly strong version!)

• Science should be based only on observable facts– The pressure exerted by a gas on the walls of its container is an

acceptable fact

– “Explaining” that pressure in terms of invisible particles is unacceptable, since the particles cannot be seen

– Heat is also a primary phenomenon

– Explaining it in terms of the motion of unseen particles is unacceptable

• For Mach, science is more description than understanding– Just study the relation between T and P, e.g. how does P change as

T is increased? Then make a catalog of results…

Boltzmann’s View

• Truth in science need not be seen directly, but is what can be consistently inferred from observations– Even though we cannot see atoms directly, the atomic hypothesis

makes predictions, e.g. about how P changes if T is increased

– If those predictions are confirmed by experiment, it provides support to the atomic hypothesis

– If many predictions that follow from the atomic hypothesis are confirmed, we may believe in the existence of atoms

• Assuming no predictions are found to be wrong!

– In effect, we “see” atoms by their effects

– Not really so different from “seeing” anything!

• This is the modern attitude

• Plus, today we can see atoms directly!

Electron Microscope Images

•

Iron on CopperXenon on Nickel

Boltzmann and Philosophy

• After Mach retired, Boltzmann returned to Vienna and was given Mach’s philosophy course to teach

• These lectures became famous, in part for their attacks on various philosophies and philosophers

• Proposed title of a talk for the VPS:– “Proof that Schopenhauer is a stupid, ignorant philophaster,

scribbling nonsense and dispensing hollow verbiage that fundamentally and forever rots people’s brains”

(These were actually Schopenhauer’s own words regarding Hegel!)

Brownian Motion

• Discovered in 1828 by Robert Brown, a botanist• He observed that microscopic pollen grains suspended in a

liquid move around erratically, even though the liquid itself has no observable motion

• Possible explanation: the grains are being jostled and buffeted by unseen atoms

• In 1905, Albert Einstein calculated the details of this process and made several predictions– E.g. how fast a collection of pollen grains should spread out

• Quickly confirmed by experiments• This convinced the remaining atom skeptics!

Einstein’s “Miraculous Year”

• In addition to the paper on brownian motion, AE published two other papers in 1905, on– The theory of relativity (including E = mc2)

• A revolutionary new view of space and time

– The “photoelectric effect” • This paper won him the 1921 Nobel Prize

• Any one of these would have made his reputation as a great scientist; together they were astounding

Case Study: “Cold Fusion”

• A (fairly) recent example of scientific practice

is 240: discovering the atom dr. dean johnston department of chemistry and biochemistry dr. david...

Documents

curved slide

astronomy slide

durant slide

lunar eclipse slide

everyday writer slide

albert einstein slide

niels bohr slide

valid way of knowing