• • Know: • Definitions of photon and Planck’s Constant.

• Energy/mass relationship equation. Only certain energy levels are permitted in atoms. Definitions of: hadron; baryon; meson; lepton; and quark. • • • • • • • • • • • Understand • The manner in which the Photoelectric Effect demonstrates the particle nature of light. • The connection between energy and mass and the fact that energy and mass can be converted into one another. An atom may be ionized (lose an electron) if it absorbs a photon with great enough energy. An electron may jump to a higher energy level if it is hit with a photon with the correct energy to make the transition – this causes atoms to ABSORB photons with very specific energies. • An electron in an excited state will naturally decay to a lower energy state, releasing a photon with energy equal to the difference in energy between the levels – this causes atoms to EMIT photons with very specific energies. All particles have corresponding anti-particles with equal mass and opposite charge. A baryon is a collection of three quarks. A meson is a pairing of a quark and an anti-quark. Leptons are indivisible and have a charge of -1 or 0. Strong nuclear force holds the nuclei of atoms together and is carried by gluons. Weak nuclear force is involved in beta decay and is carried by bosons. Electromagnetic force governs interactions between atoms; forms molecules; gives matter its shape; and is carried by photons.

Gravitational force is not explained by the Standard Model. • • • • • • • • • • • • • • • • Be able to • Determine the energy of a photon based on its frequency and/or wavelength. Determine a photon’s ‘type’ using the EM Spectrum chart. Use/interpret a graph of photon energy vs. frequency and/or frequency vs. wavelength. Determine the energy contained in a given amount of mass. Convert universal mass units MeV. Use/interpret a graph of energy vs. mass. Determine the energy needed to liberate an electron from an atom. Determine the photon energy needed to make an electron jump to a higher energy level. Determine the photon energy released when an electron drops to a lower energy level. Determine if it is possible for a particular photon to be emitted by a specific energy transition. Determine the number of possible photon energies emitted during a specific set of transitions to a lower energy state. Explain why a hot gas will have a ‘bright line’ emission spectrum. Explain why a cold gas will have a ‘dark line’ absorption spectrum. Determine the charge on a baryon; meson; or lepton. Build a baryon or meson with a specific charge. Explain the relationship between matter and anti-matter. Explain the phenomenon of beta decay.

• •

Light as a wave

Light is an electromagnetic wave produced by an oscillating _______________________. The vibrating charges produce alternating _________________________________which are perpendicular to the direction of the wave’s motion. This waves can travel through vacuum in vast space. Light is a wave because 1. Light have

wave characteristics

such as _________________________________________________ 2. Light exhibit

wave behavior

such as • However, the wave model of light

can not explain

interactions of light with matter

An unusual phenomenon was discovered in

Waves have a particle nature

An unusual phenomenon was discovered plates, a current flow is measured. A current in the early 1900's. is simply a flow of electrons in a metal, such Photoelectric_Effect If a

beam of light

is pointed at the negative end of a pair of charged plates,

a current flow is measured

which means the beam of light must be electrons from one metal plate, which are attracted to the other plate by electrostatic forces.

liberating

However, the observed phenomenon was that the current flow

varied

strongly with the

frequency

of light such that there was a

sharp cutoff

and no current flow for smaller frequencies. Only when the frequency is above a certain point (threshold frequency), the current flow

increases with

light

strength

.

Photoelectric Effect

example

Which graph best represents the relationship between the intensity of light that falls on a photo-emissive surface and the number of photoelectrons that the surface emits?

1 2 3 4

example

• When the source of a dim orange light shines on a photosensitive metal, no photoelectrons are ejected from its surface. What could be done to increase the likelihood of producing photoelectrons?

1. Replace the orange light source with a red light source. 2. Replace the orange light source with a higher frequency light source. 3. Increase the brightness of the orange light source. 4. Increase the angle at which the photons of orange light strike the metal.

example

A beam of monochromatic light incident on a metal surface causes the emission of photoelectrons. The length of time that the surface is illuminated by this beam is varied, but the intensity of the beam is kept constant. Which graph below best represents the relationship between the total number of photoelectrons emitted and the length of time of illumination?

1 3 2 4

Einstein explains photoelectric effect

•

..\..\RealPlayer Downloads\Photoelectric Effect and Photoelectric Cell.flv

•

Einstein

successful explained the photoelectric effect within the context of the new physics of the time,

quantum physics

developed by

Max Planck

. • Quantum theory assumes that electromagnetic energy is emitted from and absorbed by matter in

discrete amounts

of packets. Each packet carries a

quantum

of energy.

• The quantum, or basic unit, of electromagnetic energy is called a

photon

. A photon is a mass-less particle of light, it carries a quantum of

energy.

Energy:

E = h∙f

Energy:

E = h∙f

•

since f = c/λ E = h∙f = h∙c/λ

• The amount of energy

E

of each photon is

directly

proportional to the frequency

f

of the electromagnetic radiation, and

inversely

proportional to the wavelength

λ.

–

E

is energy of a photon, in Joules, or eV, – 1 eV = 1.60x10

-19 J – –

f h

is

Planck’s constant

, 6.63 x 10 -34 is frequency of the photon, in hertz J∙s – –

c λ

is the speed of light in vacuum, c = 3.00x10

is wavelength, in meters 8 m/s

E E f λ

example

• Which characteristic of electromagnetic radiation is directly proportional to the energy of a photon?

1. wavelength 2. period 3. frequency 4. path

Example

• The energy of a photon is 2.11 electronvolts 1. Determine the energy of the photon in Joules 2. Determine the frequency of the photon 3. Determine the color of light associated with the photon.

example

• 1.

The slope of a graph of photon energy versus photon frequency represents Planck’s constant 2. the mass of a photon 3. the speed of light 4. the speed of light squared

The Compton effect: photon-particle

•

collision

• In 1922 Arthur Compton was able to bounce an X-ray photon off an electron. The result was an electron with more kinetic energy than it started with, and an X-ray with less energy than it started with. A photon can actually interact with a particle! A photon has

momentum!!

- another proof that photon is a particle.

During the collision, both energy and momentum are conserved.

The momentum of a photon

• A photon, although mass-less, it has momentum as well as energy. All photons travel at the speed of light,

c.

The momentum of photon is

p = h/λ = h∙f/c

Where

p

is momentum,

h

is plank’s constant,

λ

is the wavelength • Momentum

p

is

directly proportional

to the frequency light, and

inversely proportional to the wavelength

.

p = h/ λ = h∙f/c E = hc/ λ = h∙f

example

• A photon of light carries 1. energy, but not momentum 2. momentum, but not energy 3. both energy and momentum 4. neither energy nor momentum

example

• All photons in a vacuum have the same 1. speed 2. wavelength 3. energy 4. frequency

example

• The threshold frequency of a photo emissive surface is 7.1 x 10 14 hertz. Which electromagnetic radiation, incident upon the surface, will produce the greatest amount of current?

1. low-intensity infrared radiation 2. high-intensity infrared radiation 3. low-intensity ultraviolet radiation 4. high-intensity ultraviolet radiation

• In conclusion, light has both wave and particle nature.

• Wave nature: – Exhibit wave characteristics: _______________________________________________________ – Exhibit wave behavior: – _______________________________________________ • Particle nature: – ________________________________________ – _________________________________ – _________________________________

Particles have

wave

nature

• Just as radiation has both wave and particle characteristics,

matter

in motion has

wave

as well as

particle

characteristics. • The wavelengths of the waves associated with the motion of

ordinary object is too small

to be detected.

• The waves associated with the motion of particles of

atomic

or

subatomic

size, such as

electrons,

can produce diffraction and interference patterns that can be observed.

All Matters have wave nature

• • All matters have wave nature.

Louis de Broglie

( French physicist and a Nobel laureate ) assumed that any particle--an electron, an atom, a bowling ball, whatever--had a "wavelength" that was equal to Planck's constant divided by its momentum...

λ = h / p

In summary

•

Waves has particle nature, it has momentum just like a particle:

p = h / λ

•

Particle has wave nature, it has a wavelength just like a wave:

λ = h / p

models of an atom

1. Describe Thompson’s model 2. Explain the strengths and weaknesses of Rutherford’s model of the atom 3. Describe Bohr model of an atom 4. Describe cloud model

• About 440BC, a Greek scientist named He called this particle an

atom Democritus

the idea that eventually, all objects could be reduces to a single particle that could not be reduced any further.

came up with , from the Greek word

atomos

which meant “

not able to be divided

matter – was born.

.” From this, the idea of the atom – the basic building block of all • Around 1700, scientists understanding of molecular composition of matter had grown considerably. They had figured out that elements combine together in specific ratios to form compounds. In 1803, British chemist

John Dalton

came up with a theory about atoms: – All substances are made of small particles that can’t be created, divided, or destroyed called atoms. – Atoms of the different elements are different from each other. (So, atoms of gold are exactly like gold atoms, but different than aluminum atoms).

same element

are

exactly alike

, and atoms of – Atoms join with other atoms to make new substances.

• In 1897, a British scientist named

JJ Thomson

discovered that

electrons

are relatively low-mass, negatively charged particles present in atoms. • Because atoms are neutral, he proposed a model - the "atom" was made of negatively-charged particles (electrons) dispersed among positively-charged particles (protons) like raisins in "

plums in a pudding

". • In 1909, British scientist

Ernest Rutherford

decided to test the Thomson theory, and designed an experiment to examine the parts of an atom.

Rutherford’s model

• In his experiment, He fired alpha particles (2 positive charges) beam at extremely thin

gold foil

.

• He expected alpha particles travel in

straight

line unaffected because the net electric force on the alpha particle would be relatively small. • However, he found a small number of particles were scattered at large

angles

.

• Rutherford explained this phenomenon by assuming the following: – Most particles were not affected due to the

vast empty space

inside the atom – Only a few particles were scattered due to the repulsive force between the

concentrated positive charge

inside the atom and the particle.

• Rutherford’s model of the atom – most of the mass was concentrated into a compact

nucleus

(holding all of the positive charge), with

electrons

occupying the bulk of the atom's space and orbiting the nucleus at a distance.

• In Rutherford’s model of the atom, electrons orbit the

nucleus

in a manner similar to planets orbiting the sun.

•

example

The diagram represents alpha particle

A

approaching a gold nucleus.

D

is the distance between the path of the alpha particle and the path for a head-on collision. If

D

is decreased, the angle of deflection θ of the alpha particle would 1. decrease 2. increase 3. remain the same

example

•

A. 1 B. 2 C. 3

Which diagram shows a possible path of an alpha particle as it passes very near the nucleus of a gold atom?

D. 4

example

• In Rutherford's model of the atom, the positive charge 1. is distributed throughout the atom's volume 2. revolves about the nucleus in specific orbits 3. is concentrated at the center of the atom 4. occupies most of the space of the atom

Limitation of Rutherford model

• According to Rutherford, electrons

accelerate

due to centripetal force, and the accelerating charges radiate electromagnetic waves,

losing

energy. So the radius of electron’s orbit would steadily

decrease

.

• This model would lead a rapid

collapse

of the atom as the electron plunged into the nucleus.

•

The Bohr Model of the hydrogen atom

Danish physicist

Niels Bohr

attempted to explain the problems in Rutherford’s model. He proposed in 1913 that electrons move around the nucleus of an atom in

specific paths

, on

different levels of energy.

1. All forms of energy are

quantized.

2. The electron in an atom can

occupy

certain specific orbits and no other.

only 3. Electrons can

jump

from one orbit to another by emitting or absorbing a

quantum of energy

in the form of photon.

4. Each allowed orbit in the atom corresponds to a specific

energy level

. The orbit

nearest

nucleus represents the smallest amount of the energy that the electron can have. The electron can remain in this orbit with out

losing

energy even though it is being accelerated.

• When electron is in any particular orbit, it is said to be in a

stationary state

. Each stationary state represents an

energy level

. The successive energy levels of an atom are assigned integral numbers, denoted by n=1, 2, 3… • When the electron is in the lowest level (

n=1

), it is said to be in the

ground state

.

• For a hydrogen atom, an electron in any level above the ground state is said to be in an

excited state.

• When electron goes up from lower to higher level, the atom

absorbs

the form of a photon. a

quantum

of energy in • When electron goes down from higher to lower level, the atom

emits

form of a photon. a quantum of energy in the

• If the energy of the photon of light is

just right

, it will cause the electron to

jump to a higher level

.

• When the electron

jumps back down

, a

photon is emitted

each jump down.

for • A photon

without the right amount

of energy (the pink one) passes through the atom with

no effect

. • Photons with

too much energy

ejected which

ionizes

the atom will cause the electron to be

Energy levels

•

excitation

: any process that raises the energy level of electrons in an atom.

• Excitation can be the result of

absorbing

the energy of colliding particles of matter, such as electrons, or of photons of electromagnetic radiation. • A photon’s energy is absorbed by an electron in an atom only if the photon’s energy corresponds

exactly

to an energy-level

difference

possible for the electron.

• Excitation energies are

different

for different atoms.

• Atoms rapidly

lose

the energy of their various excited states as their electrons return to the ground state. This lost energy is in the form of photons of specific

frequencies

, which appear as the spectrum lines in the characteristic spectrum of each

element

.

• A

spectrum line

is a particular frequency of absorbed or emitted energy characteristic of an atom.

Absorption Spectrum Emission Spectrum

example

• White light is passed through a cloud of cool hydrogen gas and then examined with a spectroscope. What is the cause of dark lines observed on a bright background?

Ionization potential

• An atom can absorb sufficient energy to raise an electron to an energy level such that the electron is removed from the atom’s bound and an

ion

is formed.

• The energy required to remove an electron from an atom to form an ion is called the atom’s

ionization potential

. • An atom in an excited state requires a

smaller

amount of energy to become an ion than does an atom in the ground state.

Energy level diagram

ionization Ground state • The energy level of an electron that has been completely removed from the atom is defined to be

0.00 eV

. All other energy levels have

negative

values.

• The electron in the ground state has the lowest energy, with largest

negative

value.

E photon = E initial - E final • This formula can be used to determine the energy of the photon emitted (+) or absorbed(-).

E photon = hf where h = 6.63 x 10 -34 Js • This formula can be used to determine the energy of a photon if you know the frequency of it. Planck's constant, h, can be used in terms of Joule(s) or eV(s). (note: the Regents reference table only gives it in terms of Js)

Energy level is explained by

Louis de Broglie’s

particle-wave theory

• According to de Broglie, particles have wave nature:

λ = h / p

• If we begin to think of electrons as waves, we'll have to change our whole concept of what an "orbit" is. Instead of having a little particle whizzing around the nucleus in a circular path, we'd have a wave sort of strung out around the whole circle. Now, the only way such a wave could exist is if a

whole number of its wavelengths fit exactly around the circle

. • If the circumference is exactly as long as two wavelengths, say, or three or four or five, that's great, but two and a half won't cut it.

..\..\RealPlayer Downloads\Quantum Mechanics- The Structure Of Atoms.flv

Limitations of Bohr’s model

• It can not predict or explain the electron orbits of elements having

many

electrons

The cloud model (

Schrödinger model)

• In this model, electrons are not confined to specific orbits, instead, they are spread out in space in a form called an electron

cloud

.

• The electron cloud is densest in regions where the probability of finding the electron is

highest

.

The cloud model represents a sort of history of where the electron has probably been and where it is likely to be

going

.

example

• The term "electron cloud" refers to the 1. electron plasma surrounding a hot wire 2. cathode rays in a gas discharge tube 3. high-probability region for an electron in an atom 4. negatively charged cloud that can produce a lightning strike

Atomic spectra

1.

Explain atomic spectra using Bohr’s model of the atom.

2. Recognize that each element has a unique emission and absorption spectrum.

Atomic spectra

• According to can be found in only certain discrete energy states.

Bohr’s

model, electrons in atoms

Atomic spectra

• When electrons jump from the lower to the higher number orbits, they

absorb

a

particular

amount of energy and we can observe the

absorption

spectrum. •When they fall back again they

release

the same amount of energy and we can observe the

emission (bright-line)

spectrum. The amount of energy absorbed or released in this way can be

directly related

to the wavelength at which we see the absorption and emission lines on the spectrum.

• Each element has a characteristic

spectrum

that differs from that of every other element. • The emission spectrum can be used to

identify

the element, even when the element is mixed with other elements.

Hydrogen spectrum Helium spectrum

Emission (bright-line, atomic) spectra

• When an electron in an atom in an excited state falls to a lower energy level, the energy of the emitted photon is equal to the difference between the energies of the initial and final states.

E

photon

= E

i

– E

f

= hf

• E i is the initial energy of the electron in its excited state and E f is the final energy of the electron in the lower energy level.

• Each energy difference between two energy levels corresponds to a photon having a specific

frequency

. • For example: An electron in a hydrogen atom drops from the

n

= 3 energy level to the

n

= 2 energy level. The energy of the emitted photon is

A specific series of frequencies, characteristic of the element, is produced when the electrons of its atoms in excited states fall back to lower states or to the ground state. When these emitted frequencies appear as a series of bright lines against a dark background, they are called a

bright-line spectrum

or an

emission spectrum.

•

example

An electron in a hydrogen atom drops from the

n

= 4 energy level to the

n

= 2 energy level. The energy of the emitted photon is

example

• A.

B.

C.

D.

Excited hydrogen atoms are all in the

n

= 3 state. How many different photon energies could possibly be emitted as these atoms return to the ground state?

1 2 3 4

example

• What is the minimum amount of energy needed to

ionize

a mercury electron in the

c

energy level?

question

• 1.

2.

3.

4.

Which electron transition in the hydrogen atom results in the emission of a photon of greatest energy?

n

= 2 to

n

= 1

n

= 3 to

n

= 2

n

= 4 to

n

= 2

n

= 5 to

n

= 3

Absorption spectra

• An atom can absorb only photons having energies

equal

to specific differences in its energy levels. • The frequencies and wavelengths of these absorbed photons are exactly the

same

as those of the photons emitted when electrons lose energy and fall between the same energy levels.

• If the atoms of an element are subjected to

white

light, which consists of all the visible frequencies, the atoms will selectively

absorb

the same frequencies that they emit when excited. The absorbed frequencies appear as dark lines in the otherwise continuous white-light spectrum. The series of dark lines is called an

absorption spectrum.

absorption Spectrum

example

A The four-line Balmer series spectrum shown in the diagram is emitted by a hydrogen gas sample in a laboratory. A star moving away from Earth also emits a hydrogen spectrum. Which spectrum might be observed on Earth for this star?

D B C

example

• An electron in a mercury atom that is changing from the

a

to the

g

level absorbs a photon with an energy of 1. 12.86 eV 2. 10.38 eV 3. 7.90 eV 4. 2.48 eV

example

• When an electron changes from a higher energy level to a lower energy level within an atom, a quantum of energy is 1. fission 2. fused 3. emitted 4. absorbed

nucleus

1. Define nuclear force 2. Describe universal mass unit 3. Use mass-energy relationship in calculations

Nuclear force

• ..\..\RealPlayer Downloads\Physical Science 7.4c - The Atomic Nucleus.flv

• The

nucleus

is the

core

of an atom made up of one or more protons (except for one of the isotopes of hydrogen) and one or more neutron. The positively charged protons in any nucleus containing more than one proton are separated by a distance of

10 -15 m.

• In the nucleus, there are two major forces: – A

large repulsive electric

(Coulomb) force between protons – A very

strong attractive nuclear force

to keep the protons together.

• It is this

nuclear force

inside a nucleus that overcomes the repulsive electric force between protons and hold the nucleus together.

Nuclear force has rather unusual properties. 1. It is

charge independent

. This means that in all pairs

neutron & neutron

,

proton & proton

, and

neutron & proton,

nuclear forces are the same. 2. at distances 10 -13 cm, the nuclear force is

attractive and very strong

,

100 times

stronger than the electromagnetic repulsion.

Strongest forces known to exist

, nuclear force is also called strong force.

3. the nuclear force very

short range force

. At distances greater than a few nucleon diameters, the nuclear attraction practically disappears. As the nucleus gets bigger, the attractive nuclear force between the nucleons gets smaller, the nucleus becomes very unstable and starts to break apart, causing radioactive decay.

example

• Which type of force overcomes the repulsive electrostatic force between protons in the nucleus of an atom?

1. magnetic 2. nuclear 3. gravitational 4. centrifugal

example

• The force that holds protons and neutrons together is known as the 1. gravitational force 2. strong force 3. magnetic force 4. electrostatic force

example

• Compared to the gravitational force between two nucleons in an atom of helium, the nuclear force between the nucleons is 1. weaker and has a shorter range 2. weaker and has a longer range 3. stronger and has a shorter range 4. stronger and has a longer range

Universal mass unit

• The universal mass unit, or atomic mass unit, is defined as

1/12

the mass of an atom of

carbon-12

, which is a carbon atom having

6 protons, 6 neutrons, and 6 electrons

.

• In universal mass unit, – the

mass of the proton is 1.0073 u,

– the

mass of the neutron is 1.0087 u

, – the mass of an

electron is 0.0005 u

. • In SI units, a mass of one universal mass unit,

1 u = 1.66 x 10 -27 kg.

1.

2.

3.

4.

example

• An atomic mass unit is defined as 1/12 the mass of an atom of

Mass-energy relationship

• • • • Einstein showed that mass and energy are different forms of the

same thing

and are equivalent.

E = mc

2

E m c

is energy in is mass in is the speed of light in vacuum

m/s joules, kg, 3.00x10

8

example

• What is the amount of energy in one kilogram of mass?

•

Kilogram is very big unit

of mass in the reference of

mass energy conversion

.

• Universal mass unit (u) is used:

1 u = 9.31 x 10

2

MeV

example

• According to the chart, the energy equivalent of the rest mass of a proton is approximately 1. 9.4 x 10 2 MeV 2. 1.9 x 10 3 MeV 3. 9.0 x 10 16 MeV 4. 6.4 x 10 18 MeV

example

• • 1.

2.

3.

4.

Approximately how much energy would be generated if the mass in a nucleus of an atom of were converted to energy?

[The mass of is 2.0 atomic mass units.] 3.2 x 10 -10 J 1.5 x 10 -10 J 9.3 x 10 2 MeV 1.9 x 10 3 MeV

question

• Which particle would generate the greatest amount of energy if its entire mass were converted into energy?

1. electron 2. proton 3. alpha particle 4. neutron

• 1.

2.

3.

4.

example

How much energy would be generated if a 1.0 x10 -3 -kilogram mass were completely converted to energy?

9.3 x 10 -1 9.3 x 10 2 MeV MeV 9.0 x 10 13 9.0 x 10 16 J J

• The graph represents the relationship between mass and its energy equivalent. The slope of the graph represents 1. the electrostatic constant 2. gravitational field strength 3. the speed of light squared 4. Planck's constant

•

example

If a deuterium nucleus has a mass of 1.53 × 10 -3 universal mass units less than its components, this mass represents an energy of 1. 1.38 MeV 2. 1.42 MeV 3. 1.53 MeV 4. 3.16 MeV

example

• The light of the "alpha line" in the Balmer series of the hydrogen spectrum has a wavelength of 6.58 × 10 -7 meter. The energy of an "alpha line" photon is approximately 1. 6.63 × 10 -34 J 2. 3.0 × 10 8 J 3. 3.02 × 10 -19 J 4. 4.54 × 10 13 J

example

• The alpha line in the Balmer series of the hydrogen spectrum consists of light having a wavelength of 6.56 x 10 -7 meter.

1. Calculate the frequency of this light.

2. Determine the energy in joules of a photon of this light.

3. Determine the energy in electronvolts of a photon of this light.

example

• The energy equivalent of the rest mass of an electron is approximately 1. 5.1 × 10 5 J 2. 8.2 × 10 -14 J 3. 2.7 × 10 -22 J 4. 8.5 × 10 -28 J

Nuclear mass and energy

• According to Einstein’s mass-energy equation, any change in energy results in an equivalent change in

mass

. Mass-energy is conserved at all levels from cosmic to subatomic. • In chemical reactions, if energy is

released

, then the total

mass must be decreased.

If energy is

absorbed

, then the total

mass must be increased

. However, the change of mass is too small to be measured.

• In nuclear reaction, the changes in energy relative to the masses involved are much larger, the corresponding change in mass can be

measured

.

Example: • total mass of two protons and two neutrons is 2(1.0073 u + 1.0087 u) =

4.0320

u • The mass of a helium-4 is

4.0016

u • The mass of the nucleus is

less

than its components. This is true for every nucleus, with the exception for hydrogen-1, which has only one nucleon.

• • •

Nuclear fission and fusion

Nuclear fission

is a nuclear reaction in which the nucleus of an atom

splits

into smaller parts (lighter nuclei ). Fission of

heavy elements

is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments ( heating the bulk material where fission takes place).

Nuclear fusion

is the process by which two or more atomic nuclei

join

together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy . The fusion of two nuclei with

lower masses

than iron (which, along with nickel , has the largest binding energy per nucleon) generally

releases energy

while the fusion of nuclei heavier than iron absorbs energy ..\..\RealPlayer Downloads\Fission And Fusion.flv

example

• If a deuterium nucleus has a mass of 1.53 × 10 -3 universal mass units less than its components, this mass represents an energy of _______________ MeV.

• 1.

2.

3.

4.

A tritium nucleus consists of one proton and two neutrons and has a total mass of 3.0170 atomic mass units. What is the mass defect of the tritium nucleus?

0.0014 u 0.0077 u 1.0010 u 2.0160 u

Studying atomic nuclei

• The structure of the atomic nucleus and the nature of matter have been investigated using

particle accelerators

.

• Particle accelerators use electric and magnetic fields to increase the kinetic energies of

charged particles

, such as electrons and protons, and project them at speeds near the speed of light.

• Collisions between the high speed particles and atomic nuclei may disrupt the nuclei and release

new particles

.

The standard model of particle physics - objectives

1. State the standard model of particle physics 2. Describe the fundamental forces in nature 3. Classify subatomic particles

Standard model of particle physics

• The

Standard Model

of particle physics (formulated ..\..\RealPlayer Downloads\CERN- The Standard Model Of Particle Physics.flv

in the 1970s) describes the universe in terms of

Matter Force

(

fermions - 24

(

bosons - 4

). ) and • Unlike the force-carrying particles, the matter particles have associated

antimatter

particles, such as the

antielectron

(also called

positron

) and

antiquarks

. So there are together

24 fermions.

The fundamental forces in nature

• There are four known forces. Two of these forces are only seen in atomic nuclei or other subatomic particles. Aside from gravity, all the macroscopically observable forces — such as friction & pressure as well as electrical & magnetic interaction —

are due to electromagnetic force

. – Gravitational – Electromagnetic – strong nuclear – Weak nuclear • ..\..\RealPlayer Downloads\The Weak and Strong Nuclear Forces (9 of 15).flv

• The

weak nuclear

force is another very short-range nuclear force that causes transformation of protons to neutrons and vice-versa, along with other

radioactive

(gives off photons and other particles) phenomena.

• The Standard Model describe the force between two particles in terms of the exchange of virtual

force carrier

particles between them.

force Strong nuclear Electro Magnetic Weak nuclear gravitational

Relative strength 10 38 range ~10 -15 m 10 10 1 36 25 ~1/r 10 -18 ~1/r 2 2 m

Force carrier gluon photon

mass 0 0

W boson W boson Z boson

80.6 GeV 80.6 GeV 91.2 GeV

graviton

0 charge 0 0 +e -e 0 0

GRAVITY

Gravitation

is a force of attraction that acts between each and every particle in the Universe. It is the

weakest

of the four fundamental forces. It is always

attractive

, never repulsive. It pulls matter together, causes you to have a weight, apples to fall from trees, keeps the Moon in its orbit around the Earth, the planets confined in their orbits around the Sun, and binds together galaxies in clusters.

THE ELECTROMAGNETIC FORCE

• The electromagnetic force determines the ways in which electrically

charged

particles interact with each other and also with magnetic fields. This force can be

attractive or repulsive.

• This force holds the atoms together.

• This force also governs the emission and absorption of light and other forms of electromagnetic radiation.

THE STRONG NUCLEAR FORCE

• The strong nuclear force

binds together the protons and neutrons

that comprise an atomic nucleus and prevents the mutual repulsion between positively charged protons from causing them to fly apart. • The strong nuclear force interaction is the underlying source of the vast quantities of energy that are liberated by the nuclear reactions that power the stars.

THE WEAK NUCLEAR FORCE

• The weak nuclear force causes the

radioactive decay

of certain particular atomic nuclei. In particular, this force governs the process called

beta decay

whereby a neutron breaks up spontaneously into a proton, and electron and an antineutrino.

LONG-RANGE and SHORT RANGE FORCES

• The strong and weak nuclear interactions are effective only over extremely

short

distances. The range of strong force is about 10 -15 meters and that of the weak force is 10 -18 meters.

• In contrast, the electromagnetic and gravitational interactions are

long-range

forces, their strengths being inversely proportional to the square of distance.

Force carriers

• According to modern quantum theories, the various fundamental forces are conveyed between real particles by means of virtual particles. The force-carrying particles (which are known as

gauge bosons

) for each of the forces are as follows: – electromagnetic force -

photons

; – weak nuclear interaction - very massive

'W'

and

'Z

'

bosons

; – strong nuclear interaction – gravitation -

graviton

.

gluons.

force

Strong (nuclear)

Relative strength Range of force

1 ~ 10 -15 m

Force carrier

gluon electromagnetic 10 -2 ~ 1/r 2 photon

mass

0 0 weak

The fundamental forces

gravitational charge 0 0 10 -13 10 -38 < 10 -18 m ~ 1/r 2 W boson W boson Z boson graviton 80.6 GeV 80.6 GeV 91.2 GeV 0 +e -e 0 0

example

1. Which force is responsible for a neutron decaying into a proton? 2. Which force bonds quarks together into particles like protons and neutrons? 3. Which force governs the motion of an apple falling from a tree?

4. What are you made of? What forces hold you together?

Sub-Atomic Particles

• Although the Proton, Neutron and Electron have been considered the fundamental particles of an atom, recent discoveries from experiments in atomic accelerators have shown that there are actually

12

fundamental particles (with 12 antiparticles). Protons and neutrons are no longer considered fundamental particles in this sub-atomic classification.

Matter

Hadrons (held together by strong force) Leptons (no strong Force)

Baryons(3 quarks) Protons and neutrons Mesons (quark & anitquark) The fundamental particles are classified into two classes:

quarks and leptons

Hadrons and lepton

• Particles can be classified according to the types of

interactions

they have with other particles.

• A particle that interacts through the strong nuclear force, as well as the electromagnetic, weak and gravitational forces is called a

hadron

.

• A particle that interacts through the electromagnetic, weak and gravitational forces, but

not

the strong nuclear force, is called a

lepton

.

Hadrons – baryons & mesons

• •

Hadrons

group can be subdivided into

baryons

and

mesons

.

– Baryons are made of

three quarks

, the charges on a baryon can be

0, +1, or -1

– examples of baryons are

neutrons, protons.

– The term "baryon" is derived from the Greek

βαρύς

(

barys

), meaning "

heavy.

“

Mesons

are made a

quark

-

antiquark

pair, mesons is a particle of

intermediate

mass.

• All

hadrons

are constructed of

quarks.

A

baryon

is made up of 3 quarks, for example: A

proton

consists of up, up, down quarks A

neutron

consists of up, down, down quarks When quarks combine to form baryons, their

charges

add algebraically to a total of

0, +1, -1.

example

• Baryons may have charges of 1. +1e and + 4/3 e 2. +2e and +3e 3. -1e and +1e 4. -2e and - e

question

• Protons and neutrons are examples of 1. positrons 2. baryons 3. mesons 4. quarks

What are the Leptons?

• A

lepton

has a

mass much less than

proton, the

lepton

that of a classification of sub-atomic particles consists of 6

fundamental particles

: – Electron – Muon – Tau – Electron Neutrino – Muon Neutrino – Tau Neutrino • The

reference tables

give the names, symbols and charges of the six members of the lepton family.

Electron, Muon and Tau Leptons

• The

Electron

remains a fundamental particle, as if was in the Atomic Theory. It has an electrical charge of (-1) and plays an active role in chemical reactions.

• The

Muon

is primarily a result of a high-energy collision in an atomic accelerator. The Muon is similar to an Electron, only

heavier.

• The

Tau

particle is similar to a Muon, only

heavier yet.

• Muon and Tau particles are unstable and exist in nature for a very

short time

.

Neutrinos

•

Neutrinos

are small and have

no electrical charge

. This makes them extremely difficult to detect. They can possess a large amount of energy and the very rare times they do collide with another particle, that energy can be released.

• There are

3 types

of neutrinos: –

Electron Neutrino

, which has no charge and is extremely difficult to detect –

Muon Neutrino

, which is created when some atomic particles decay –

Tau Neutrino

, which is heavier than the Muon Neutrino .

Quarks

• • Another group of sub-atomic particles are the

Quarks

. Just like their name, they exhibit unusual characteristics. There are

6

fundamental particles among the Quarks are:

Up

and

Down

Quarks •

Charm

,

Strange

,

Top

and

Bottom

Quarks • Other particles are made up of

combination of Quarks

.

• The

reference table

gives the names, symbols, and charges of the six quarks.

Up and Down Quarks

• The

Up Quark

(+2/3). The has an electrical charge of

Down Quark

charge of (-1/3).

has an electrical • The

Proton

is made up of two Up Quarks and one Down Quark. The electrical charge of the proton is then: (+2/3) + (+2/3) + (-1/3) = (+1).

• The

Neutron

is made up of one Up Quark and two Down Quarks. The resulting electrical charge of the Neutron is: (+2/3) + (-1/3) + (-1/3) = (0).

Charm, Strange, Top and Bottom Quarks

• The

Charm Quark

has the same electrical charge as the

Up Quark

but is heavier. The

Top Quark

is then heavier than the Charm.

• The

Strange Quark

has the same electrical charge as the

Down Quark

but is heavier. The

Bottom Quark

is heavier than the Strange.

hadrons Particles in matter leptons baryons mesons 3 quarks quark and antiquark 6 types of quarks 6 types

antiparticle

• An

antiparticle

is associated with each particle. • An antiparticle is a particle having mass, lifetime, and spin identical to the associated particle, but with

charge

of

opposite sign magnetic moment

(if charged) and reversed in sign. An antiparticle is denoted by a bar over the symbol of the particle.

• Example:

p

, stands for antiproton, which can be described as a stable baryon carrying a unit negative charge, but having the same mass as a proton.

• A

positron

(

+e)

is a particle whose mass is equal to the mass of the electron and whose positive electric charge is equal in magnitude to the negative charge of the electron. • •

Positron is the antiparticle of electron Antiparticle for a neutrino

(e). • The

antineutron (n)

has the same mass as the neutron and is also electrically neutral. However the

magnetic moment

and spin of the antineutron are in the same direction, whereas, the magnetic moment and spin of the neutron are in opposite directions.

is identical to the neutrino except for their

direction of spin

.

quarks antiquarks leptons antileptons 6 6 6 There are total of

24

basic particles 6

antimatter

•

Antimatter

is material consisting of atoms that are composed of antiprotons, antineutrons, and positrons.

example

• The subatomic particles that make up both protons and neutrons are known as 1. electrons 2. nuclides 3. positrons 4. quarks

example

• According to the Standard Model, a proton is constructed of two up quarks and one down quark (

uud

), and a neutron is constructed of one up quark and two down quarks (

udd

). During beta decay, a neutron decays into a proton, an electron, and an electron antineutrino. During this process there is a conversion of a

1. u

quark to a

d

quark

2. d

quark to a meson 3. baryon to another baryon 4. lepton to another lepton

example

• A lithium atom consists of 3 protons, 4 neutrons, and 3 electrons. This atom contains a total of 1. 9 quarks and 7 leptons 2. 12 quarks and 6 leptons 3. 14 quarks and 3 leptons 4. 21 quarks and 3 leptons

example

• A top quark has an approximate charge of 1. -1.07 ×10 -19 C 2. -2.40 ×10 -19 C 3. +1.07 ×10 -19 C 4. +2.40 ×10 -19 C

example

• Compared to a proton, an alpha particle has – Hint: An alpha particle is a helium nucleus.

1. the same mass and twice the charge 2. twice the mass and the same charge 3. twice the mass and four times the charge 4. four times the mass and twice the charge

example

• What is the charge-to-mass ratio of an electron?

example

• • • During the process of beta (β-) emission, a neutron in the nucleus of an atom is converted into a proton, an electron, an electron antineutrino, and energy.

neutron energy proton + electron + electron antineutrino + Based on conservation laws, how does the mass of the neutron compare to the mass of the proton?

1. The mass of the neutron is greater than the mass of the proton. 2. The mass of the proton is greater than the mass of the neutron. 3. The masses of the proton and the neutron are the same.