Honors Nuclear RadiationHonors Nuclear Radiation

In your notebook, write a paragraph In your notebook, write a paragraph describing how our understanding of the describing how our understanding of the atom has changed over time.atom has changed over time.

Getting Inside the AtomGetting Inside the Atom

Atomic StructureAtomic Structure

Dalton’s Atomic TheoryDalton’s Atomic Theoryin 1808in 1808

All matter is composed of extremely small particles All matter is composed of extremely small particles called atoms.called atoms.

Atoms of a given element are identical in size, mass, and Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in other properties; atoms of different elements differ in size, mass, and other properties.size, mass, and other properties.

Atoms cannot be subdivided, created, or destroyed.Atoms cannot be subdivided, created, or destroyed.

Dalton’s Atomic Theory, Dalton’s Atomic Theory, continuedcontinued

Atoms of different elements combine in Atoms of different elements combine in simple whole-number ratios to form chemical simple whole-number ratios to form chemical compounds.compounds.

In chemical reactions, atoms are combined, In chemical reactions, atoms are combined, separated, or rearranged.separated, or rearranged.

Modern Atomic TheoryModern Atomic Theory

Not all aspects of Dalton’s atomic theory have proven to be Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that:correct. We now know that:

Some important concepts remain unchanged.

• Atoms are divisible into even smaller particles.• A given element can have atoms with different

masses.

• All matter is composed of atoms.

• Atoms of any one element differ in properties from atoms of another element.

Discovery of the Subatomic Discovery of the Subatomic ParticlesParticles

For the better part of 70 years Dalton’s ideas remained unchanged.For the better part of 70 years Dalton’s ideas remained unchanged.

In 1897, using Cathode ray tubes, J.J. Thomson reported that In 1897, using Cathode ray tubes, J.J. Thomson reported that cathode rays were made up of negatively charged particles in cathode rays were made up of negatively charged particles in motion.motion.

Figure 3.7: Schematic of a cathode ray tube.Figure 3.7: Schematic of a cathode ray tube.

Plum Pudding model of an atom.Plum Pudding model of an atom.

Discovery of the Atomic Discovery of the Atomic NucleusNucleus

More detail of the atom’s structure was provided in 1911 by Ernest More detail of the atom’s structure was provided in 1911 by Ernest Rutherford and his associates Hans Geiger and Ernest Marsden.Rutherford and his associates Hans Geiger and Ernest Marsden.

The results of their gold foil experiment led to the discovery of a The results of their gold foil experiment led to the discovery of a very densely packed bundle of matter with a positive electric very densely packed bundle of matter with a positive electric charge.charge.

Rutherford called this positive bundle of matter the Rutherford called this positive bundle of matter the nucleus.nucleus.

Figure 3.5: Rutherford’s Figure 3.5: Rutherford’s experiment.experiment.

Figure 3.6: Results of foil experiment if Plum Figure 3.6: Results of foil experiment if Plum Pudding model had been correct.Pudding model had been correct.

Figure 3.6: Actual Results.Figure 3.6: Actual Results.

Discovery of the ProtonDiscovery of the Proton

19191919 Ernest RutherfordErnest Rutherford

Discovery of the neutronDiscovery of the neutron

19321932 James ChadwickJames Chadwick

The Structure of the AtomThe Structure of the AtomAn An atomatom is the smallest particle of an element that is the smallest particle of an element that

retains the chemical properties of that element.retains the chemical properties of that element.

The The nucleusnucleus is a very small region located at the is a very small region located at the center of an atom.center of an atom.

The nucleus is made up of at least one positively The nucleus is made up of at least one positively charged particle called a charged particle called a protonproton and usually one and usually one or more neutral particles called or more neutral particles called neutronsneutrons..

Fundamental ParticlesFundamental Particles(The Standard Model)(The Standard Model)

Part IPart I

Fundamental Particle – Fundamental Particle – The MeaningThe Meaning

It is understood that the universe is It is understood that the universe is composed of particles.composed of particles.

Currently, the leptons and quarks appear Currently, the leptons and quarks appear to qualify as the true to qualify as the true fundamental/elementary particles; fundamental/elementary particles; meaning without structure.meaning without structure.

The organization of known fundamental The organization of known fundamental particles – particles – The Standard ModelThe Standard Model

“ “The standard model of particle physics The standard model of particle physics is a theory which [currently] describes is a theory which [currently] describes three of four known fundamental three of four known fundamental interactions between the elementary interactions between the elementary particles that make up all matter…particles that make up all matter…

It is a quantum field theory developed It is a quantum field theory developed between 1970 and 1973 which is between 1970 and 1973 which is consistent with both quantum mechanics consistent with both quantum mechanics and special relativity.”and special relativity.”

“…“…the standard model falls short of the standard model falls short of being a complete theory of fundamental being a complete theory of fundamental interaction, primarily because of it’s lack interaction, primarily because of it’s lack of inclusion of gravity, the fourth known of inclusion of gravity, the fourth known fundamental interaction.”fundamental interaction.”

The particle nature of the standard The particle nature of the standard model consists of two groups:model consists of two groups:

- Matter Particles- Matter Particles

- Force-Mediating Particles- Force-Mediating Particles

Matter ParticlesMatter Particles

The matter component of the Standard The matter component of the Standard Model is comprised of twelve particles. Model is comprised of twelve particles.

These particles all have an intrinsic spin These particles all have an intrinsic spin value of ½, making them conform to the value of ½, making them conform to the Pauli Exclusion Principle.Pauli Exclusion Principle.

All matter particles of the Standard Model also All matter particles of the Standard Model also have corresponding antimatter particles. These have corresponding antimatter particles. These particles breakdown into groups of quarks (up, particles breakdown into groups of quarks (up, down, strange, charm, top, and bottom) and down, strange, charm, top, and bottom) and leptons (electron, muon, tau, and leptons (electron, muon, tau, and corresponding neutrinos).corresponding neutrinos).

Quarks and leptons are further grouped into Quarks and leptons are further grouped into sets known as generations. sets known as generations.

Quarks carry color charges (red, blue, or Quarks carry color charges (red, blue, or green) so they participate in strong green) so they participate in strong interactions.interactions.

The up, charm, and top quarks carry the The up, charm, and top quarks carry the electric charge (+2/3).electric charge (+2/3).

The down, strange, and bottom quarks The down, strange, and bottom quarks carry the electric charge (-1/3).carry the electric charge (-1/3).

This allows the quarks to participate in This allows the quarks to participate in electromagnetic interaction.electromagnetic interaction.

Leptons are color neutral and do not Leptons are color neutral and do not participate in strong interaction.participate in strong interaction.

The electron, muon, and tau particles The electron, muon, and tau particles carry the electric charge (-1) and carry the electric charge (-1) and participate electromagnetic interaction.participate electromagnetic interaction.

Neutrinos have no electric charge and do Neutrinos have no electric charge and do not participate in electromagnetic not participate in electromagnetic interactions.interactions.

Quarks and leptons carry flavor charges Quarks and leptons carry flavor charges and participate in weak nuclear and participate in weak nuclear interactionsinteractions..

Force-Mediating Particles Force-Mediating Particles

Force-mediating particles of the Force-mediating particles of the Standard Model group into three Standard Model group into three categories that correspond with three of categories that correspond with three of the four fundamental interactions.the four fundamental interactions.

All three mediating particles are bosons All three mediating particles are bosons and have intrinsic spins of (1).and have intrinsic spins of (1).

This allows these particles to not conform This allows these particles to not conform to the Pauli Exclusion Principle.to the Pauli Exclusion Principle.

Photons are electromagnetic force Photons are electromagnetic force mediators involving charge particles.mediators involving charge particles.

Photons are considered massless Photons are considered massless particlesparticles. .

WW++, W, W--, and Z, and Zo o gauge bosons are weak gauge bosons are weak nuclear mediators involving particles of nuclear mediators involving particles of different flavors (quarks and leptons).different flavors (quarks and leptons).

WW++, W, W--, and Z, and Z00 bosons are massive bosons are massive particles.particles.

Gluons are strong nuclear force-Gluons are strong nuclear force-mediators involving color charged mediators involving color charged particles (quarks).particles (quarks).

Gluons are considered massless particles.Gluons are considered massless particles.

Part IIIPart III

The Higgs particle – The Higgs particle – The ChallengeThe Challenge

The Standard Model predicts the The Standard Model predicts the existence of one more particle known as existence of one more particle known as the “Higgs boson.”the “Higgs boson.”

The Large Hadron Collider (LHC) at The Large Hadron Collider (LHC) at CERN is hoped to confirm the existence CERN is hoped to confirm the existence of the Higgs boson in the near future.of the Higgs boson in the near future.

Quarks

• Protons and neutrons are composed of quarks.

• There are six different types of quarks.

u up (+2/3)d down (-1/3)t top (truth)b bottom (beauty)c charms strange

Atomic StructureAtomic Structure

u

u

d

d

u

d