Download Na has an atomic mass of 22.989769 u. Using the information below

Unit 4A: ATOMIC STRUCTURE
 Describe matter as containing discrete positive and negative charges
Periodic Table: Theories of atomic structure began with an attempt to explain the
chemical properties (reactivity) of the elements. Mendeleev was able to arrange
the 63 known elements in his time, into a table. Horizontally the elements were
arranged according to increasing atomic mass. Vertically the elements were
arranged according to chemical properties. Today the horizontal arrangement is
by atomic number rather than atomic mass.
Scientific experiments help develop our modern theory of the atom. We will
explore those different experiments and how the atom’s model changed.
CATHODE RAYS:
 Explain how the discovery of cathode rays contributed to the development
of atomic models
 Explain J.J. Thomson’s experiment and the significance of the results for
both science and technology
 Perfom an experiment, or simulation, to determine the charge-to-mass
ratio of the electron
 Determine the mass of an electron and/or ion, given appropriate empirical
data
 Derive a formula for the charge-to-mass ratio that has input variables that
can be measured in an experiment using electric and magnetic fields.
The invention of cathode ray tubes (discharge tubes) in the mid 1800’s led to the
discovery of the electron. With CRT’s scientists were able to investigate electric
discharge across a spark gap.
CRT:
The tube contains a low pressure gas.
Discharge tubes always discharge from the cathode. Cathode rays were found to
have a number of characteristics – some are similar to EMR and some different:
Similar:
 Cathode rays travel in straight lines
 Cathode rays cause similar chemical reactions to light.
Different:
 Cathode rays could be deflected by magnetic fields
 Cathode rays could be deflected by electric fields
 The characteristics of cathode rays are always the same, regardless of the
material comprising the cathode.
Because of the differences, it was determined that cathode rays were NOT EMR.
Two scientists associated with cathode rays are;
Crookes who believed that cathode rays consisted of particles and
J.J. Thomson who measured the charge to mass ratio of cathode rays as q/m =
1.76 x 1011 C/kg.
Cathode rays became known as electrons!
Thomson passed high energy/high speed cathode rays through a circular anode
with a hole in the center. The rays then passed through a magnetic field which
deflected them in a circular arc. The centripetal force causing the ray to travel in
a circular arc is given by:
The centripetal force is caused by the magnetic field so that Fc= Fm:
B and r were easy to measure but v could not be measured directly.
Thomson adjusted the experiment by adding a section in which he passed the
electrons through BOTH electric and magnetic fields FIRST. The fields were
adjusted until the forces were equal, causing the electrons to travel in a straight
line: mathematically:
Since both the electric field strength E and the magnetic field strength B could be
found, Thomson was able to find the speed of the electrons. Knowing the
electrons speed Thomson was able to use the relationship from above to
calculate the q/m (e/m) ratio for an electron.
Pg 285-288 (#1-7 )
Thomson Model of the Atom
After doing his experiment with CRT and finding the q/m ratio for the particles,
Thomson formulated a theory on the structure of the atom. In Thomson’s model
the atom was full of a positive fluid. The ‘electrons’ (negative particles of the
cathode ray) were embedded in the positive fluid. Thomson’s model was
otherwise known as the ‘raisin bun model’ or the ‘plum pudding model’.
If you recall Millikan’s experiment where he balanced the gravitational forces with
the electrostatic forces on oil drops, Millikan was able to determine the
elementary charge (smallest possible charge).
By combining the two experimental results of Thomson and Millikan, one could
find the mass of the negative cathode particles – electrons – assuming that they
are elementary particles and therefore have the elementary charge! The mass of
the electron has now been theorized!
Workbook page 120 #4-12
Rutherford’s Scattering Experiment
 Explain, qualitatively, the significance of the results of Rutherford’s
scattering experiment, in terms of scientists’ understanding of the relative
size and mass of the nucleus and the atom.
In 1911, Ernest Rutherford and his associates did a series of experiments in which
they fired alpha particles from a radium source contained in a lead block. The
alpha particles were directed at a thin gold foil. If the Thomson model were true,
the alpha particles should have passed through the foil with very little deflection
since the mass of the Thomson’s atom is evenly distributed.
However, in Rutherford’s experiment, some of the particles were scattered at
quite large angles and some even bounced backwards! This did not fit with
Thomson’s model.
Rutherford concluded that the mass of the atom was not evenly distributed
through the atom as in Thomson’s model. In order for the large angles of
deflection, the mass must be concentrated in a very small region of the atom
which he called the nucleus. Rutherford suggested that alpha particles passing
close to the nucleus could be deflected through large angles due to electrostatic
repulsion and momentum. Alpha particles hitting the nucleus could be deflected
backwards.
Rutherford was also able to determine that the nucleus contained all the positive
charge of the atom.
To prevent the electrons from collapsing in to the nucleus (due to electrostatic
attraction), it was theoretically necessary that the electrons orbit the nucleus like
the earth orbits the sun.
Rutherford’s model had a serious physical problem. According to classical
physics, a particle in orbit has centripetal acceleration; and according to
Maxwell’s theory of EMR, any charged particle accelerating should emit energy
(EMR). If it emits energy continuously, then the electron should eventually lose
its orbit and fall into the nucleus.
Draw Rutherford’s model (Classical Model of atom) and name 3 new conclusions
that Rutherford incorporated into his atomic model.
Pg 285-288 (rest)
Spectra and atomic models
 Describe that each element has a unique line spectrum
 Explain, qualitatively, the characteristics of, and the conditions necessary to
produce continuous line-emission and line-absorption spectra
 Predict the conditions necessary to produce line-emission and lineabsorption spectra
 Observe spectra
 Identify elements represented in a sample line spectra by comparing them
to representative line spectra of elements
The spectrum of hydrogen gas led to the explanation of the problem with the
Rutherford model and the development of the Bohr model.
There are 3 types of spectra:
1. Continuous: this spectra is produced when the light from a heated/glowing
solid is passed through a prism or diffraction grating. In this spectrum all
frequencies are given off and one color fades into another continuously as
in a rainbow.
2. Emission: (Bright-line spectra) produced when the light from an excited gas
passes through a diffraction grating or prism. The spectrum consists of
certain frequencies only, so there is no continuous rainbow, but rather
specific bands of color. Each gaseous element is unique in that it has its
own spectrum. This is used in chemical analysis to determine what types of
elements are present.
3. Absorption: (Dark-line spectra) produced when light from a glowing solid
passes through a cooler unexcited gas before passing though a diffraction
grating or prism. The continuous spectrum that would ordinarily be
produced has dark lines (absorption lines or Fraunhofer lines) because the
gas absorbs certain frequencies. This is seen with solar spectrum and
allows us to determine the atmosphere around solar objects.
What is most interesting is that the emission spectra and the absorption
spectra of the same gas are completely opposite. The dark lines of the
absorption match the bright lines of the emission for the same gas.
See pg 749-752.
Hydrogen spectra:
http://csep10.phys.utk.edu/astr162/lect/light/absorption.html
Bohr atom:
 Explain, qualitatively, how emission of EMR by an accelerating charged
particle invalidates the classical model of the atom
 Explain, qualitatively, the concept of stationary states and how they explain
the observed spectra of atoms and molecules
 Calculate the energy difference between states, using the law of
conservation of energy and the observed characteristics of an emitted
photon.
 Predict the possible energy transitions in the hydrogen atom, using a
labelled diagram showing energy levels
The emission spectra for hydrogen gas became known as the BALMER series.
Bohr’s theory came mainly for the explanation of the spectrum for hydrogen.
Niels Bohr developed a theory about atomic structure to explain why orbiting
electrons do not collapse into the nucleus. Bohr’s model was based on two
conclusions:
1. There are certain allowed orbits around the nucleus in which the electron
can move without giving off energy. This means that the energy of the
electron is quantized. (start of the Quantum model)
2. In order for the electron to occupy a given orbit, it must have the energy
allowed for that orbit.
In this model, the electron can move up to a higher energy level (orbit) by
absorbing energy or down to a lower energy level (orbit) by emitting energy; but
it cannot be found between energy levels (orbits).
http://www.upscale.utoronto.ca/PVB/Harrison/BohrModel/Flash/BohrModel.ht
ml
The Bohr model states that only photons of certain frequency can be absorbed or
emitted. It also explains why the atom does not collapse as only certain orbits are
allowed.
There are numerous possible transitions even for the hydrogen atom of only one
electron.
The visible light seen in the emission spectra is called the Balmer series but many
others exist and produce EMR of other forms.
Conservation of Energy can be used to calculate the energies involved in the
electron transitions. An electron in the first energy level for hydrogen is -13.6 eV
or -2.18 x 10-18 J.
What would the negative sign mean?
If red light of 654 nm is given off in the Balmer transition from level 3 to level 2,
and level two has an energy of -3.4 eV, what is the energy of level 3?
The important point to remember is that the energy an electron gains or loses during a
transition is the result of a loss or gain by another particle or photon.
Transition energy(often EMR) = energy of upper level-energy of lower level
The energy of any other orbit in hydrogen can be calculated using the formula En=E1/n2. The
squared function should be a reminder that the energy between levels is NOT uniform, but
exponential.
Bohr’s model was also used to explain the periodicity of the periodic table. Bohr suggested
that chemical properties depended on the number of electrons in the outer energy level (orbit).
The outer orbit is called the valence orbit and the electrons in this orbit are called valence
electrons. Only certain numbers of electrons are allowed in a given level.
Elements that have the same number of valence electrons in their outer orbit have similar
chemical properties.
The Bohr model has both strengths and weaknesses.
Strengths:
1. It explained the repetition of chemical properties in the periodic table and is very easy
to draw and useful to use in Chemistry
2. It explained the hydrogen spectra
Weaknesses:
1. It could not explain the spectra of elements other than hydrogen.
2. It could not explain why only certain orbits were allowed.
3. It could not explain why spectral lines are split into several lines in the presence of an
electric or magnetic field.
4. It could not explain the differences in the brightness of spectral lines.
The Bohr model was improvement on earlier models but it was not the final model.
292-295
QUANTUM MODEL OF THE ATOM
 Explain, qualitatively, how electron diffraction provides experimental
support for the deBroglie hypothesis
 Describe, qualitatively, how the two-slit electron interference experiment
shows that quantum systems, like photons and electrons, may be modelled
as particles or waves, contrary to intuition.
In unit 3 we looked at how DeBroglie explained that particles could exhibit wave
behavior.(this is only significant for sub-atomic particles)
By applying this to electrons, it is explained that electrons can only exist in certain
orbits because they need to form a standing wave (no destructive interference
amoung each other).
Therefore: C = 2πrn which needs to = nλ : 2πrn= nλ for orbitals
By substituting De Broglie’s definition for wavelength of particles λ=h/mv into the
orbital equation you get:
2πrn = nh/mv
The wave nature of matter provides a natural explanation for the quantized
energy levels.
The wavelength of the electron gets longer in each successive energy level
because the electron’s speed decreases as the radius of the orbit increases.
Schrodinger derived an equation for determining how electron waves behave in
the electric field surrounding the nucleus. The equations involve functions. Max
Born interpreted these functions to involve probability of distribution of the
electrons. An orbital is now defined as the probability distribution of an
electron in an atom.
Unlike the Bohr model, the quantum model does not have electrons orbiting at
precisely defined distances, but behaving as waves which do not have a precise
location. This is called quantum indeterminacy – Heisenberg uncertainty
principle.
Disadvantage: the quantum model cannot be visualized like the Bohr model.
http://plus.maths.org/content/schrodinger-1
Read pg 782
Compare and contrast, qualitatively, the classical and quantum models of the
atom.
Debroglie 296-298
Pg 300-302
Unit 4B
Radioactivity:
Radioactivity was discovered in 1896 by Henri Becquerel.
Rutherford discovered the nucleus in 1911.
Henry Moseley discovered the charge on the nucleus was always a multiple of the
same charge of an electron in 1913.
Frederick Soddy discovered isotopes and Chadwick discovered the neutron in
1932.
So, by 1932, a fairly good understanding of the nucleus and elementary particles
was underway.
Three Elementary particles as of 1932:
Electron
Proton
Neutron
Charge (C)
Mass (kg)
-1.60 x 10-19
+1.60 x 10-19
0
9.11 x 10-31
1.673 x 10-27
1.675 x 10-27
Atomic Mass
Units (u)
0.000549
1.0073
1.0087
1u = 1.660 x 10-27kg
Protons and neutrons are both contained in the nucleus and are known
collectively as nucleons.
The nucleus of an atom may be represented using:
X = symbol of element
A = mass number  number of nucleons
Z = atomic number  number of protons
Isotopes:
Isotopes are atoms of the same element that differ in the number of neutrons.
Because they belong to the same element, they must have the same number of
protons.
Eg.
Pg 313
Mass Spectrometers
A mass spectrometer separates particles according to their masses. The
spectrometer has four basic components:
Ion source
velocity selector
ion separation region and ion
detector
Ions are produced by heating or electrical discharge. The ions are accelerated by
an accelerating voltage.
Because the ions have different velocities, a velocity selector is used. The velocity
selector consists of magnetic and electric fields which deflect particles that do not
have the right velocity. Particles which are not deflected (pass straight through)
have a velocity given by:
After the velocity selector, the ions enter a perpendicular magnetic field which
deflects the particles in a circular path given by
If the mass of particles is different, then the radii will be different.
If the charge of particles is different, then the radii/direction of deflection will be
different.
(remember the CRT tube experiment of Thomson – very similar)
Pg 154-159
Forces
 Relate, qualitatively and quantitatively, the mass defect of the nucleus to
the energy released in nuclear reactions, using Einstein’s concept of massenergy equivalence.
 Express mass in terms of mega electron volts per c2 when appropriate
Binding neutrons and protons together in a nucleus requires a very large force to
overcome the electrostatic repulsions of protons. This force is called the strong
nuclear binding force. It is one of the four natural forces in the Universe that
scientist have identified.
1.
2.
3.
4.
Gravitational forces
Electromagnetic forces (electric, magnetic, and contact forces)
Strong nuclear forces
Weak nuclear forces
http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html
The strong nuclear force is not fully understood but it does have a very limited
range (1 x 10-15 m) and it is by far the STRONGEST of the four forces. Sometimes
even this force is not adequate to keep the nucleus together and the nucleus
either disintegrates and /or rearranges itself. This activity is known as
radioactivity.
Radioactivity often releases some of the energy involved in holding the nucleus
together (binding energy).
How to measure binding energy:
We take the difference in mass when the nucleus is together versus the mass of
separate individual particles. The difference between the two numbers tells us
the MASS DEFECT. According to Einstein, mass defect and energy can be equated
with his famous formula:
E=mc2
Where m= mass defect
The energy involved in binding the nucleus lowers the relativistic mass of the
atom as compared to the mass of the individual particles.
mdefect = mindividual particles- mrelativistic (measured)
( or Ebinding= Enucleons- Enucleus)
Whenever the nucleus undergoes some change, some mass is converted into
energy (heat).
Eg1. Sodium
23
Na
11
has an atomic mass of 22.989769 u. Using the
information below;
1u=1.660539 x 10-27
1p=1.007825 u
1n= 1.008665 u
c=2.997925 x 108m/s
a. find the mass defect for this nucleus.(in kg)
b. Find the binding energy.(in J)
Energy equivalence for a particle is often expressed in MeV/c2. This is the
calculated energy using E=mc2.
Eg. 1u=931.4941 MeV (communicated as MeV/c2)
Prove :
Therefore if you find the mass defect for the question above, in ‘u’, a shortcut is
to just multiply it by 931.4941:
Pg 333-336
Types of Radioactivity
 Describe the nature and properties, including the biological effects, of
alpha, beta and gamma radiation
 Write nuclear equations, using isotope notation, for alpha, beta-negative
and beta-positive decays, including the appropriate neutrino and
antineutrino
 Use the law of conservation fo charge and mass number to predict the
particles emitted by a nucleus
 Predict the penetrating characteristics of decay products
 Interpret common nuclear decay chains
The radiation given off when a nucleus changes comes in 3 types:
1. Alpha rays2. Beta rays3. Gamma raysBiological damage is caused when radiation deposits its energy in living tissue.
The nature and size of the charge on the three types of radiation affect their
damaging abilities. Alpha particles will interact more strongly, then beta, while
gamma interactions are NOT described by electrical interactions (no charge).
Factor 1-Electrically charged radiation (alpha and beta) deposit energy
continuously, but not uniformally, as they travel through tissue.
-Beta are much less massive than alpha and are therefore more easily
scattered during interactions with atomic nuclei (less direct paths through
materials). (a fly through a crowded room) Much lower ionization effects.
-Alpha particles ionize virtually every molecule they pass. (a tank through a
crowded room)
Factor 2- Energy content in the radiation also affects the tissues. Gamma
radiation damage is determined by the energy it has.
-Gamma radiation has to be high enough to free an electron and therefore
ionize molecules.
Three ionization effects:
1. Production of free radicals from water (unstable charges)
2. Breaking bonds in large molecules destroying their function.
3. Genetic damage to DNA molecules
They differ in terms of penetrating ability with gamma rays being the most
penetrating and alpha rays being the least penetrating.
When an unstable nucleus rearranges itself, one or more of these radiation types
are emitted. The atom changes from one element to another if alpha or beta rays
are emitted. The atom is then said to have transmuted or decayed.
Bioeffects pg 310-311
Safety is improved when working with radioactive material by:
 Decreasing exposure time
 Increasing distance between people and the radioactive material
 Increasing the shielding used.
1. Alpha decay
2. Beta decay
Gamma decay
With just a gamma decay the nucleus emits a high-energy photon but does not
change element – therefore there is no reaction to write. However, gamma rays
are generally associated with the other forms of decay because it is believed that
the atom is in an excited state when it decays and that it emits a photon as it
drops to a lower state.
In alpha and beta decay, the original nucleus is called the parent nucleus and the
product is called the daughter nucleus:
Often during the decays the daughter isotope is also radioactive (unstable)
leading to further decays. The decay process continues until a stable isotope is
reached. This is called a decay series and is often graphed:
http://en.wikipedia.org/wiki/File:Radioactive_decay_chains_diagram.svg
pg 315-318
Half-life
 Perform simple, nonlogarithmic half-life calculations
 Graph data from radio-active decay and infer an exponential relationship
between measure radioactivity and elapsed time
The rate of radioactive decay may be expressed as the ‘half-life’ or ‘activity’ of the
substance.
1. Activity – the number of nuclei that change in a given period of time. This is
often measured with a Geiger-Mueller counter for radiation.
2. Half-life – the time required for ONE HALF of a radioactive
sample to decay.
To calculate the amount remaining after a given time has passed, we can use a
formula that involves the half-life:
Amount remaining can be measured in a variety of units as the N/No is a ratio and
the units only have to match each other. The ratio of N/No may be made in terms
of activity, mass of the substance, or a % remaining.
http://mcat-review.org/atomic-nuclear-structure.php
pg 320-328
Other types of Nuclear Reactions:
 Compare and contrast the characteristics of fission and fusion reactions
 Compare the energy released in a nuclear reaction to the energy released
in a chemical reaction on the basis of energy per unit mass of reactants.
1. Artificial Transmutation
In 1919 Rutherford was the first scientist to artificially transmute an atom.
He did so by bombarding nitrogen-14 with an alpha particle to produce
oxygen-17.
Today particle accelerators are used to accelerate bombarding particles to
high speed. All elements beyond Uranium in the periodic table are the
result of artificial transmutation.
http://www.lhc.ac.uk/
2. Fission
Nuclear fission was discovered in 1938 when Fermi bombarded Uranium
with low energy neutrons. This process split the uranium nucleus into two
roughly equal parts and released large amounts of energy. The energy is
produced because some of the mass is changed into energy during the
transmutation.
The amount of energy produced may be calculated using Einstein’s
equation!
In this nuclear reaction 3 neutrons are also freed:
These three neutrons can cause further splitting –the beginning of a chain
reaction.
In a reaction where the 3 neutrons are NOT controlled an EXPLOSION
(nuclear bomb) occurs. If the 3 neutrons are controlled you have a
nuclear reactor. Read Pg 812
In a nuclear reactor 1.0 kg of U235 produces 2million times as much
energy as burning 1 kg of coal!!!
One of the major problems with nuclear fission is that it produces
radioactive isotopes which produce harmful alpha, beta and gamma
radiation. This means that the spent fuel must be stored for centuries.
http://www.howstuffworks.com/nuclear-power.htm
3. Fusion
Fusion is the opposite of fission. In fusion small nuclei are joined together
to form a larger nucleus.
Pg814 (above process)
This reaction occurs in the sun. High temperature are needed for fusion
reactions (100million K) because the positive charges of the nuclei naturally
repel one another and it takes great energy to get the nuclei close enough
for the strong nuclear force to bond them together.
Pg 330-331, 337
PAIRS PRODUCTION:




Explain how the analysis of particle tracks contributed to the discovery and identification of the
characteristics of subatomic particles
Predict the characteristics of elementary particles, from images of the tracks in a bubble
chamber, within an external magnetic field
Analyze, qualitatively, particle tracks for subatomic particles other than proton, electron and
neutrons
Use hand rules to determine the nature of the charge on a particle
Positrons were discovered in 1929 by Carl Anderson (Nobel Prize): an electron and a positron may be
created when high energy photons (gamma rays or high energy X-rays) collide with matter. For law of
conservation of charge, when an electron is produced, a positron must also be produced with it. In a
magnetic field these two particles would deflect in opposite directions (opposite charge) but with the
same radius (mass is the same).
The photon produces an electron and positron! Energy is converting to mass! With modern physics it is
possible to observe other pairs-production (energy to mass); production of a pair with opposite
charge/equal mass.
Calculate the energy that must be in the photon to produce the electron/positron pair: E=mc2
m=2x9.11 x 10-31kg E=1.64 x 10-13 J or 1.02 MeV
therefore since 2 particles of equal mass are produced their unit for mass could be 0.51 MeV/c2. m=E/c2
this is the common unit for mass of subatomic particles. Electron =0.511 MeV/c2 ;proton = 938.3
MeV/c2 ;and neutron=939.6MeV/c2
1 MeV/c2=1.7827 x 10-30 kg
The opposite must also be true too! (Mass to energy) and is termed annihilation. When the two
antiparticles meet they annihilate each other and become energy.
Building Blocks of Matter

Explain, qualitatively, in terms of the strong nuclear force, why high-energy particle accelerators
are required to study subatomic particles
Particle Accelerators:
Must have-a source of charged particles, a means of accelerating them, and a tube or container
in which they accelerate.
Particle Detectors: read pg830-831 pearson
cloud chambers (1910-1960); a device that uses trails of droplets of condensed vapour to show the
paths of charged particles. The chamber is dust-free air supersaturated with vapour from a liquid such
as water or ethanol. A charged particle speeding through will ionize some molecules along its path.
These trigger condensation forming a cloud along the path of the particle. Like a jet-liner through the
air.
Bubble chamber (developed in 1952); contains a liquefied gas like hydrogen, helium, propane, or xenon.
Ions form by a charged particle zipping through and causing it to boil. It forms a trail of tiny bubbles or
what is known as particle tracks. These particle tracks can be analyzed and a charge-to-mass ratio
obtained from them.
Neutral particles do not create tracks in either chamber! Pg339 workbook
Pg 339-343
Standard Model:



Describe the modern model of the proton and neutron as being composed of quarks
Compare and contrast the up quark, the down quark, the electron and the electron neutrino,
and their antiparticles, in terms of charge and energy (mass-energy)
Describe beta-positive and beta-negative decay, using first-generation elementary fermions and
the principle of charge conservation
-in the 1950’s more elementary particles were discovered and our view of the atom as having 3 particles
became confusing. This is due to the particle collision research using particle accelerators and pairsproduction.
1. Elementary particles (proton,neutron, electron) are made up of smaller particles called quarks-The
standard model. It is consistent with quantum theory and special theory of relativity.
2. There are two kinds of elementary particles:
fermions and bosons
fermions-responsible for matter
bosons-responsible for forces
3. fermions have two kinds: quarks and leptons
quarks:
symbol
u
d
s
c
b
t
Up
Down
Strange
charm
Bottom
Top
Charge
2/3
-1/3
-1/3
2/3
-1/3
2/3
There are also six antiquarks –have a line over the symbol and an opposing charge. *All elementary
particles have an antiparticle.
-protons, neutrons, and pions are called hadrons and are made up of quarks. A quark can not
be isolated, it just exists inside a hadron.


If they consist of 3 quarks they are called a baryon eg. Proton and neutron.Proton: uud
note the charge!
Neutron: udd *write the neutron to proton/electron reaction using the quark
model
If they consist of a quark and antiquark they are called mesons eg. Pion:ud
Leptons: can be isolated. Also six types:
Electron
Muon
Tau
Electron neutrino
Muon neutrino
Tau neutrino


Symbol
e


e


charge
-1
-1
-1
0
0
0
The only stable lepton is the electron. The neutrinos have no charge and almost no
mass.
They too have antileptons (line over top of the symbol and opposite charges-if
applicable)
4. Of the four fundamental forces, they all act within the atom except gravitational forces. These forces
have carriers (Bosons) that are other particles:



The force carrier for the electromagnetic forces is the photon.
The force carrier for the strong nuclear force is the gluon
The force carrier for the weak nuclear force is the W+, Wo, and Z bosons
The standard model is not complete as it does not include the gravitational force. Another theory that
tries to unify the description of the universe as forces is the string theory; elementary particles are
thought of as very short strings (one-dimensional) that can vibrate in different modes. Each mode
corresponds to a certain particle.
(‘New periodic table’ in folder)
Pg 346-350 workbook