Chapter 4 (Partial)
Structure of the Atom
4.1 Early Theories of Matter (& Early Chemistry
– Alchemy and Related)
4.2 Subatomic Particles & Nuclear Atom
4.2.5 Ultimate Structure of Matter – The
Standard Model (Not in Book)
Section 4.1 Early Ideas About Matter
The ancient Greeks tried to explain
matter, but the scientific study of the
atom began with John Dalton in the early
1800's.
• Compare and contrast the atomic models of
Democritus, Aristotle, and Dalton.
• Describe the activities related to the chemical sciences
that occurred between the time of Aristotle and the
early 19th century when Dalton’s theory was published.
• List the components of Dalton’s atomic theory.
• Explain how Dalton's theory explains the conservation
of mass.
Section 4.1 Early Ideas About Matter
(Cont.)
• Identify the components of Dalton’s theory that are not
strictly correct and provide examples of why they
aren’t.
• Name the two instruments that are routinely used to
obtain images of atoms.
• Describe the basic operational principles of the
Scanning Tunneling Microscope (STM).
Section 4.1 Early Ideas About Matter
Key Concepts
• Democritus was the first person to propose the
existence of atoms.
• According to Democritus, atoms are solid,
homogeneous, and indivisible.
• Aristotle did not believe in the existence of atoms.
• John Dalton’s atomic theory is based on numerous
scientific experiments.
• The scanning tunneling microscope (STM) and the
modified scanning transmission electron microscope
(modified STEM) are instruments capable of atomic
scale imaging.
Early Philosophers
Thought matter formed of:
• Earth
• Air
• Fire
• Water
History: Development of Atomic Model
Atomic Theory Timeline
Democritus
Aristotle
Boyle
Lavoisier
Dalton
J. Dalton
Empedocles
Aristotle
J. Proust
A. Lavoisier
Democritus
Leucippus
R. Boyle
Zeno
-500
-250
R. Bacon
0
250
500
750
1000
1250
1500
1750
2000
Democritus Greek, 460-370 BC
First to propose matter was not
infinitely divisible = concept of atom
Democritus, Greek Philosopher
(460-370 BC)
His theory: Matter could not be
divided into smaller and smaller
pieces forever, eventually the
smallest possible piece would
be obtained
This piece would be indivisible
Named the smallest piece of
matter “atomos,” meaning “not
to be cut”
Democritus – Atomic Theory
To him, atoms were small,
hard particles that were all
made of same material but
were different shapes and
sizes
Atoms were infinite in
number, surrounded by
empty space, and always
moving and capable of
joining together
Democritus’ Concept of Matter
•
•
•
•
•
Matter is empty space through which
atoms move
Atoms are solid, homogeneous,
indestructible, indivisible
Different kinds of atoms have different
sizes and shapes
Differing properties of matter are due to
atoms size, shape, & movement
Changes in matter result from changes
in groupings of atoms and not changes
in atoms themselves
Aristotle Greek Philosopher
(384-322 BC)
14 years old when Democritus
died
Believed matter made of 4
basic elements (earth, air, fire
and water)
Disagreed with Democritus believed matter was
continuous (did not accept
idea of the “void”)
His ideas endured for 2000 yrs
Alchemy for 2000 years
Aristotle believed any
substance could be
transmuted (transformed)
into any other substance
simply by changing
relative proportions of the
4 basic qualities
This mindset dominated
quest for new substances
done by the alchemists
Alchemy for 2000 years
During
Idea
of the
transmutation
search for ability
laid foundation
to transmute
for alchemy
matter
(e.g.,
change
leadsearching
into gold),forthey
did a lot
of
Alchemists
were
evolution
from
good
experimentation
that laid
for
ignorance
to enlightenment
by foundation
searching for:
modern
• elixir ofscience
life (source of eternal life/youth)
• philosopher’s stone (substance to turn base
metals into gold; also el. of life)
• aqua vitae (“water of life” – concentrated
ethanol solution – whiskey etc)
• panacea (substance meant to cure all
diseases)
Alchemy
"The hopeless pursuit of the
practical transmutation of
metals was responsible for
almost the whole of the
development of chemical
technique before the
seventeenth century, and
further led to the discovery
of many important
materials.”
http://www.levity.com/alchemy/
Alchemy
http://en.wikipedia.org/wiki/Alchemy
Popular belief is that Alchemists made
contributions to the "chemical" industries of
the day—ore testing and refining,
metalworking, production of gunpowder, ink,
dyes, paints, cosmetics, leather tanning,
ceramics, glass manufacture, preparation of
extracts, liquors, and so on
Alchemists contributed distillation to
Western Europe
Science During 1600’s to1800’s
Scientists were
discovering concepts and
relationships by doing
large, basic experiments
with stoves, pots, ovens,
and basic glassware,
much of which had been
developed by alchemists
With observable
properties came
explanations!
Robert Boyle 1627-1691
Sometimes referred to as
Father of Modern Chemistry
One of first to publish all
experimental details of his
work, including experiments
that did not work
Boyle revived Democritus’
ideas by proposing that a
substance was not element
if it were made of two or
more components
Robert Boyle ~ 1660
Best known for his quantitative work
with gases (Boyle’s Law)
Still believed in alchemy – that metals
could be converted into gold
Was first to propose existence of
elements in the modern sense
Boyle considered a substance to be an
element unless it can be broken down
into simpler substances
Marie-Anne and Antoine Lavoisier
1743-1794
Mother and father of
modern chemistry?
Studied various types of
reactions involving
oxygen: respiration,
burning, rusting
Antoine Lavoisier (France) ~1760
Studied chemical reactions
quantitatively
Credited with being first to propose law
of conservation of matter
Lavoisier
Was sure that air contained > one element
Was able to determine amount of “reacting
component” in air - named this component
oxygen
Lavoisier
Pictured experiment demonstrates Law of
Conservation of Mass
Lavoisier
Law of Conservation of Mass
There is no detectable change in total
mass of materials when they react
chemically to form new materials
Mass of products will equal mass of
reactants in a chemical reaction
During chemical reaction, matter
neither created nor destroyed
Joseph Proust (France, 1754-1826)
~1794 Studied chemical composition of
compound copper carbonate (CuCO3)
Found all samples of CuCO3 had same
relative composition of elements by mass:
5.3 parts Copper: 4 parts Oxygen: 1 part
Carbon
This finding led to law of definite proportion
John Dalton (1766-1844)
A schoolteacher!
Devised Law of
Multiple Proportions
“when two elements
form more than one
compound, they
come together in
whole number ratios”
John Dalton (1766-1844)
Used work of Lavoisier,
Proust, and Gay-Lussac
to revive Democritus’
idea that matter was
made of atoms
Based much of his
theory on
• Law of Conservation
of Mass
• Law of Constant
Composition
John Dalton’s Atomic Theory
Matter made up of atoms. Atoms of
given element identical.
Atoms can’t be created, destroyed or
divided.
All atoms of one element have the same
mass. Atoms of two different elements
have different masses.
Atoms may combine in the ratio of
small, whole numbers to form
compounds. In chemical reactions,
atoms are separated, combined, or
rearranged.
John Dalton’s Atomic Theory
1. Matter composed of extremely small
atoms
2. Atoms of given element are identical
3. Atoms of different elements are different
4. Can’t be created, divided, or destroyed
5. Different atoms combine in whole
number ratios to form compounds
6. In chemical reactions, atoms are
separated, combined or rearranged
Dalton’s Atomic Theory
Experimental evidence
• looked at mass ratios of compounds
Theory explained conservation of mass
Element A Element B
mass = mA mass = mB
Compound
AB2
mass =
mA + mB
Dalton’s Atomic Theory
Slightly wrong about
• Indivisibility of atoms (subatomic particles)
• All atoms of same element having identical
properties (isotopes)
• Although atoms themselves not created or
destroyed, slight changes in mass occur as
energy absorbed/released (thanks to
James Kong & A Einstein)
• “Exotic” matter (neutron stars, plasmas,
dark matter, etc) not composed of atoms
as such (thanks to Adam Sorrentino)
Atom Definition
Smallest particle of an element that
retains the property of the element
This simple definition does not deal
with the reality uncovered by modern
nanotechnology research – individual
atoms or small clusters of atoms of an
element do not always behave in the
same way as a bulk sample of the
element
Imaging Atoms
Atom diameters ~ 0.1 to 0.5 nm (water
molecule diameter ~0.3 nm)
Techniques exist to “image” atoms (not
really “seeing” them in the conventional
sense of the word)
Not readily available until STM
commercialized (see following)
http://en.wikipedia.org/wiki/Scanning_tunneling_microscope
Schematic of STM
http://www.iap.tuwien.ac.at/www/surface/STM_Gallery/stm_schematic.html
STM Operation
Based on “tunneling current”
• Starts to flow when sharp tip
approaches conducting surface at
distance of ~ 1 nm
• Current extremely sensitive to distance
Tip mounted on a piezoelectric tube
• Allows tiny movements by applying a
voltage at its electrodes
STM
Electronics control tip position so
tunneling current (tip-surface distance)
is kept constant while scanning a small
area of the sample
Movement recorded - displayed as an
image of the surface topography
Under ideal circumstances individual
atoms of a surface can be resolved
STM – Moving Atoms
Modified STM can be used as a tool for
picking up, moving, and putting down
atoms
Imaging Atoms: Modified Scanning
Transmission Electron Microscope
http://physicsworld.com/cws/article/print/23440
In 2002, IBM researchers and their
collaborators modified an electron
microscope; allowed clear images at the
atomic scale to be made
Modified electron microscope is second
major instrument to provide images of
atoms
Can’t be used to move atoms like STM type
instruments
Practice
Early & current theories of matter
Problems 1- 5, page 91
Problems 29 – 33, page 112
Chapter 4 (Partial)
Structure of the Atom
4.1 Early Theories of Matter
4.2 Subatomic Particles & Nuclear Atom
4.2.5 Ultimate Structure of Matter – The
Standard Model (Not in Book)
Section 4.2 Defining the Atom
An atom is made of a nucleus
containing protons and neutrons;
electrons move around the nucleus.
• Define atom.
• Distinguish between the subatomic particles in terms
of relative charge and mass.
• Describe the structure of the atom, including the
locations of the subatomic particles and the relative
sizes of the atom and the nucleus.
• Identify the scientists that contributed to the discovery
of the nature of the atom and be able to describe their
specific contribution and the experiment on which their
discovery was based.
Section 4.2 Defining the Atom
Key Concepts
• An atom is the smallest particle of an element that
maintains the properties of that element.
• Electrons have a 1– charge, protons have a 1+
charge, and neutrons have no charge.
• An atom consists mostly of empty space surrounding
the nucleus; the size of the atom relative to the size is
the nucleus is about 10,000.
Crookes (Cathode Ray) Tube
See page 92, Figure 4-7
Effect of Electric and/or Magnetic
Fields on Electron Trajectory
Discovering the Electron
From cathode ray
tube experiments, it
was determined that
rays:
• Were actually
stream of charged
particles
• Carried negative
charge
J J Thomson
Discovering the Electron
Thomson (1856-1940)
• Measured effect of electric and
magnetic fields on cathode ray to
determine ratio of charge to mass (q/m)
for electron
• From comparison with known (q/m)
values, concluded that electron mass
much less than hydrogen atom  must
be a subatomic particle
• Did not determine actual value of mass
Discovering the Electron
Millikan (1868-1953)
• Determined charge on electron

from oil drop experiment (see following)
• From mass/charge ratio (previously
determined by Thomson), calculated
electron mass, me
me = 1/1840 mass of hydrogen atom
Millikan’s Oil Drop Experiment
Ions produced by energetic radiation
(X-rays)
Some ions attach to oil droplets, giving
them a net charge
Fall of droplet in electric field between
the condenser plates is speeded up or
slowed down, depending on the
magnitude and sign of charge on
droplet
Millikan’s Oil Drop Experiment
Atom
izer
Electrically charged
condenser plates
Millikan’s Oil Drop Experiment
Analyzed data from a large number of
droplets
Concluded that the magnitude of
charge (q) on a droplet is an integral
multiple of electronic charge (e)
q=ne
(where n = 1, 2, 3, . . . ).
Plum Pudding Atomic Model
AKA “chocolate chip cookie dough” model
Proposed by Thomson
+
+
Electrons
(negative)
+
Smeared out “pudding”
of positive charge with
negative electron
“plums” imbedded in it
Nuclear Atom (Rutherford)
Rutherford devised test to distinguish
between plum pudding and nuclear
models
• Plum pudding – cloud of positive charge
• Nuclear – concentrated positive charge
Plum pudding model advantage:
+ charges can avoid each other
Alpha particle deflection from gold foil
Concluded that there must be nucleus
Rutherford’s Experiment
Alpha Particles
Striking Screen
Radioactive
Sample
Lead Box
Gold
Foil
Fluorescent
Screen
Rutherford Scattering Experiment
Some deflected
Most go straight
through
Some bounced
back!
Rutherford Scattering Experiment
Over 98% of alpha particles went straight
through
About 2% of alpha particles went through
but were deflected by large angles
About 0.01% of alpha particles bounced off
gold foil
“...as if you fired a 15” canon shell at a
piece of tissue paper and it came back
and hit you.”
Rutherford Scattering Experiment
Alpha particles
should pass right
through the atoms
with minimum
deflection
Expected Result
(plum pudding)
Rutherford Scattering Experiment
Expected Result
(plum pudding)
Actual Result
(nuclear model)
Rutherford Conclusions
Atoms contain a
positively charged,
small core, called
nucleus
Note: structure of
nucleus (as protons) not
yet known
Most of atom is empty
space
Discovery of Protons
Protons (discovered
1920 – Rutherford)
• Nucleus contained
positively charged
particles called
protons
• Charge equal and
opposite to that of
electron
Missing Anything?
Shouldn’t protons repel each other?
Since electrons weigh nothing compared to
protons…
If beryllium atom has 4 protons, mass
should be ~ 4 amu
Actual mass 9.01 amu! Where is extra
mass coming from?
Need more experiments!
Discovery of Neutron
Neutron (discovered 1932
– James Chadwick)
• Nucleus contained
subatomic particles
called neutrons
• No charge
• Mass nearly equal to
that of proton
General Features of the Atom
Nuclear Atom – Relative Sizes
If entire atom were
represented by a room,
5 m x 5 m x 5 m, the
nucleus would be
about the size of a
period in the textbook
Nucleus diameter is ~
1/10,000 diameter of
an atom
Atom Components
See table page 97, table 4-1
Particle Symbol
Electron
eProton
p+
Neutron
n0
Relative mass
1/1840
1.000
1.001
Summary: key events in discovery of
nature of matter for chemists
~400 BC
~350 BC
1803
1897
1910
1911
1919
1932
Democritus’ Atomic Theory (not accepted)
Aristotle elements: earth, air, fire, & water
John Dalton’s Atomic theory began forming
J. J. Thompson discovers electron
Robert Millikan determines charge on electron
Ernest Rutherford discovers positive nucleus
Ernest Rutherford discovers proton - evidence for
proton as a constituent of nucleus
James Chadwick discovers neutron
Practice
Subatomic particles & nuclear atom
Problems 6 - 9, page 97
Problems 34 - 46, page 112
Chapter 4 (Partial) - Structure of the Atom
4.1 Early Theories of Matter
4.2 Subatomic Particles & Nuclear Atom
4.2.5 Ultimate Structure of Matter – The
Standard Model (Not in Book)
Section 4.2.5 Ultimate Structure of Matter –
The Standard Model
The Standard Model describes the
fundamental particles of nature and the
forces that act between particles.
• List and describe the fundamental particles of nature.
• List the four fundamental forces and their relative
strengths; know that bosons are the carriers of force.
• Describe hadrons, baryons, mesons, quarks and
leptons and be able to identify their component
particles (if they are not themselves fundamental).
Section 4.2.5 Ultimate Structure of Matter –
The Standard Model
• List the 6 kinds of quarks and the 6 kinds of leptons.
• Describe how the proton, the neutron and the electron
fit into the classification of matter under the Standard
Model.
• Describe the nature of antimatter and the method by
which is was both predicted and experimentally
verified.
• Describe the role that large particle accelerators such
as the Large Hadron Collider (LHC) play in discovering
new information about the nature of matter.
4.2.5 Ultimate Structure of Matter – The
Standard Model (Not in Book)
Standard Model Intro – Particles & Forces
The Emptiness of Matter
Fundamental Forces
Sub-structure of particles
Matter and Anti-Matter
Tracing Development of Ideas via Nobel Prizes
Tools of the Trade – Fermilab and CERN (LHC)
Beyond proton/neutron/electron Picture
Textbook, page 114
“... scientists have determined that protons
and neutrons have their own structures.
They are composed of subatomic particles
called quarks. These particles will not be
covered in this textbook because scientists
do not yet understand if or how they affect
chemical behavior. As you will learn in later
chapters, chemical behavior can be
explained by considering only an atom’s
electrons .”
Beyond proton/neutron/electron Picture
(not in book)
To understand nucleus and how some
nuclear radiation processes occur,
need to examine both structure of
nucleons (proton, neutron) and forces
acting at nuclear distances
The standard model of physics
attempts to describe all known forces
and elementary particles
What Is Matter ?
Matter is all the “stuff” around you!
Big picture (from standard model):
Matter
Hadrons
Baryons Mesons
Quarks
Anti-Quarks
Leptons
Charged Neutrinos
Elementary
Particles
Forces
Gravity
Weak
Strong
EM
Standard Model Summary
The Standard Model (SM) is our current
best description of the particles of which
matter is made and the forces which govern
these particles
SM describes 4 fundamental forces
SM describes 12 elementary particles: 6
kinds of quarks and 6 kinds of leptons (not
counting anti-particles)
Particles come in two major categories:
hadrons and leptons
Hadrons
Particles Built from Quarks Hadrons
Hundreds of hadrons have been
observed
Except for proton & neutron, they are
unstable - half lives < 0.1 s
Free neutron (outside nucleus) is
unstable – half life 10.2 min
Particles in Standard Model
Six leptons are all elementary particles –
includes the electron
“Ordinary” matter
All other particles (hadrons) are composed
of combinations of quarks (6 kinds) –
isolated quarks are not permitted
Class of hadrons called baryons composed
of 3 quarks – includes proton & neutron
Class of hadrons called mesons composed
of 2 quarks (quark + anti-quark)
Dimensions of
Subatomic
Particles
Structure Within the Atom
If protons and neutrons were 10 cm across,
then quarks and electrons would be < 0.1
mm in size and entire atom would be ~ 10
km across
Space is mostly “empty space”
Atoms > 99.999% empty space
Electron
Nucleus
Protons & Neutrons are >
99.999% empty space
g
u
Proton
Quarks make up
negligible
fraction of
protons volume !!
u
d
The Universe
The universe and all the
matter in it is almost all
empty space !
(YIKES)
Why does matter appear
to be so rigid ?
Forces, forces, forces !!!!
Primarily strong and electromagnetic
forces which give matter its solid
structure
Strong force  defines nuclear size
Electromagnetic force  defines
atomic size
Standard Model
Four Fundamental Forces
In order of decreasing strength:
Strong – binds nucleons
Electromagnetic – “opposites attract”
Weak – involved in radioactive decay
(beta decay)
Gravity
Forces arise through exchange of a
mediating field particle (a boson)
Four Fundamental Forces
?
Forces and Particles
Gravity and electromagnetic force act
between all particles with mass and charge,
respectively
Leptons not composed of quarks, so aren’t
subject to strong force, but are subject to
weak force
Quarks subject to all four forces
Attractive force between nucleons (protons,
neutrons) is byproduct of strong force, since
nucleons are composed of quarks
The Nucleus
Proton Neutron
Concentrated positive charge in nucleus
Nucleus should repel and blow apart
But nucleons have a deeper structure
Standard Model - Forces
Neutrons and protons in nucleus held together
by strong force, which has a short range
Strong force able to overcome strong electric
repulsion of + charged protons
Electromagnetic (EM) force between charged
particles (electrons attracted to nucleus)
Weak force involved in neutron decay –
involves changing one type of quark into 2nd
type with electron emission
Matter mostly empty space; forces, especially
EM forces, make it seem like it isn’t
Forces In The Atom
Electrons held in
place by
electromagnetic
force
Nucleons held
together by
strong force
Force
Strong
Electromagnetic
Gravity
Carrier Particles
(Bosons)
Gluons
Photons
Gravitons?
Getting
weaker
Standard Model
Fundamental Particles and Force Carriers
All 6 quarks and 6
leptons have
corresponding
antiparticles with
opposite charge
Some particles
are their own
antiparticles
Standard Model - Generations
Higgs Boson
(gravitron)
??
EM
Strong
Weak
Standard Model Summary
Up & down quarks (in the form of neutrons
and protons) and electrons are constituents
of ordinary matter
Individual quarks cannot be isolated
Other leptons and particles containing
quarks can be produced in cosmic ray
showers or in high energy particle
accelerators; these particles are all shortlived
Each particle has corresponding antiparticle
Matter & Forces from Standard Model
Matter
Hadrons
Baryons Mesons
Leptons
Charged Neutrinos
Quarks
Anti-Quarks
Proton & neutron
in this group
Forces
Gravity
Weak
Electron in
this group
Strong
EM
Gen
I
II
III
Each
generation
is more
massive –
takes
higher
energy to
create
Gen
I
II
III
The Proton – Not Elementary
Proton made of three quarks
Two Up
Quarks
One Down
Quark
Up quark has charge +2/3 and mass of (approximately) 1/3
Down quark has charge –1/3 and mass of (approximately) 1/3
Mass = 1/3 + 1/3 + 1/3 = 1
Charge = 2/3 + 2/3 – 1/3 = +1
The Neutron – Not Elementary
Neutron also made of three quarks
Two Down
Quarks
One Up
Quark
Mass = 1/3 + 1/3 + 1/3 = 1
Charge = 2/3 – 1/3 – 1/3 = 0
Neutrons can decay
Matter - Elementary Particles
Proton & neutron are both baryons
Proton: 2 up quarks and 1 down quark
Neutron: 1 up quark and 2 down quarks
The three elementary particles that make up
ordinary matter (atoms) are the up quark,
the down quark, and the electron
Physicist’s perspective: ordinary matter is
composed of 2 kinds of baryons and one
type of lepton
Beta Decay In Neutron
neutron
proton
W– boson
electron
neutrino
Example of weak force, of which W– is the boson
Antimatter – Paul Dirac
In 1928, wrote down equation which combined
quantum theory (developed in 1920s by
Schrodinger and Heisenberg) and special
relativity (1900s, Einstein), to describe
behavior of electron
Equation could have two solutions, one for
electron with positive energy, and one for
electron with negative energy
But in classical physics (and common sense!),
energy of particle must always be a positive
number!
http://livefromcern.web.cern.ch/livefromcern/antimatter/history/AM-history01.html
Antimatter – Paul Dirac
Dirac interpreted this to mean that for every
particle that exists there is a corresponding
antiparticle, exactly matching the particle but
with opposite charge
For electron, for instance, there should be an
"antielectron" identical in every way but with a
positive electric charge
In Nobel Lecture, Dirac speculated on
existence of completely new Universe made
out of antimatter!
http://livefromcern.web.cern.ch/livefromcern/antimatter/history/AM-history01.html
Antimatter – Carl Anderson
1932, young professor at Caltech, studied
showers of cosmic particles in cloud chamber;
saw track left by "something positively charged,
and with the same mass as an electron"
After nearly 1 year of effort and observation,
decided tracks were actually antielectrons, each
produced alongside an electron from impact of
cosmic rays in cloud chamber
Called antielectron "positron", for its positive
charge. discovery gave Anderson the Nobel Prize
in 1936 and proved existence of antiparticles as
predicted by Dirac
http://livefromcern.web.cern.ch/livefromcern/antimatter/history/AM-history01-a.html
Antimatter – Carl Anderson
Anderson's cloud chamber picture of cosmic
radiation from 1932 showing for first time
the existence of anti-electron
Particle enters from
bottom, strikes lead
plate in middle and loses
energy as can be seen
from greater curvature of
upper part of track
http://www.aps.org/publications/apsnews/200408/history.cfm
http://livefromcern.web.cern.ch/livefromcern/antimatter/history/AM-history01-a.html
Standard Model Development
Developed and verified by careful
analysis of high energy physics
experiments (particle accelerators and
colliders) along with further
development and refinement of
quantum mechanics
Also requires improved experimental
equipment, methods, analysis
techniques
Current Work
Large accelerator experiments at Fermilab
(Illinois) [stopped operation Oct 2011] and
at CERN (Switzerland/France) in the Large
Hadron Collider (LHC) done to search for
new particles and test Standard Model
predictions
LHC
Technology Review (MIT) May/June 2008 By Jerome Friedman
The recently completed Large Hadron Collider,
the world's most powerful particle accelerator and
most ambitious scientific instrument, is being
readied to address some of the deepest
questions in physics.
Hundreds of feet below the surface of the earth,
straddling the Swiss-French border near Geneva,
it will smash counter-rotating, seventrillionelectron-volt beams of protons against one
another in a 27-kilometer ring of superconducting
magnets.
LHC
With this immense energy, the LHC will be
capable of producing new types of particles that
are thousands of times heavier than the proton.
And it will enable physicists to study phenomena
at one-ten-billionth the scale of the atom.
The science will be carried out with five
multisystem particle detectors, the most massive
of which are Atlas and CMS. Atlas is comparable
in size to a seven-story building, 135 feet long
and 75 feet wide; CMS, a somewhat smaller but
heavier detector, weighs more than one and a
half times as much as the Eiffel Tower.
Compact Muon Solenoid
CMS (high energy
particle physics detector)
at CERN lab (Geneva)
An example of one of the
LHC particle detectors
END