* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download r - Purdue Physics
Nuclear transmutation wikipedia , lookup
Metallic bonding wikipedia , lookup
Molecular Hamiltonian wikipedia , lookup
Chemical bond wikipedia , lookup
Photoelectric effect wikipedia , lookup
Particle-size distribution wikipedia , lookup
Chemistry: A Volatile History wikipedia , lookup
X-ray fluorescence wikipedia , lookup
Atomic orbital wikipedia , lookup
Gaseous detection device wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
Geiger–Marsden experiment wikipedia , lookup
History of molecular theory wikipedia , lookup
Condensed matter physics wikipedia , lookup
Matter wave wikipedia , lookup
Hydrogen atom wikipedia , lookup
Nuclear binding energy wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Valley of stability wikipedia , lookup
Electron configuration wikipedia , lookup
Wave–particle duality wikipedia , lookup
Elementary particle wikipedia , lookup
Lecture 31 April 12. 2017. With the assumption of small slit width and large distance x to the screen the expanded Y view of the two slits light beams are parallel. S1 d S2 Screen x sin x x n d Bright fringes when n=0 or an integer +1,+2, ……. Constructive interference y If the screen is far from the slits sin can be approximated by sin , thus we x have bright fringe condition dy x n y n d x Dark fringes occur when n is an odd integer n = 2m+1 of y (2m 1) 4/13/2017 x d 2 Physics 214 Spring 2016 2 1 Cathode Ray Tube and Thomson's discovery of electrons, particles and photons Cathode Ray Tube and Röntgen’s discovery of X-ray photons Black Body radiation and Max Planck’s quantum hypothesis: E h Photo Electric Effect and its interpretation by Einstein Discrete Hydrogen Gas Discharge Spectrum and the Balmer – Rydberg -Ritz formula (1908) Bohr’s hypothesis of Hydrogen Atom a.) Electron orbits around proton in Coulomb field b.) Only certain orbits are permitted c.) Photons are emitted or absorbed in these transitions d.) Electrons do not radiate when in the stable orbits Periodic Table and Rutherford’s Experiment Nuclear structure and radioactivity 4/13/2017 Physics 214 Spring 2016 2 Improvements of Guericke of Magdeburg’s pump and Volta – Galvani’s battery resulted in a high vacuum and high voltage cathode ray tube. Upon heating the cathode, three kind of beams (1897) emerged: particles particles particles We identified the particle with Helium nucleus particle with the electron of Benjamin Franklin by Thomson in 1897. See Fig. 18.7 and 18.8 on page 393. particle with high energy photon by Röntgen. See Fig. 18.10 and 18.11 on page 394. 4/13/2017 Physics 214 Spring 2016 3 Max Planck painted black the inside of a closed cube and drilled a small hole on one of its side and measured the distribution of of the emitted (black body) radiation. Max Planck could explain the observed spectral distribution of the black body radiation only if he assumed that the relation between the energy and frequency of the radiation is E h Using this relation Einstein could explain the Photo Electric Effect Ee h and obtain the Nobel prize. 4/13/2017 Physics 214 Spring 2016 4 Planck’s relation and its interpretation by Einstein suggests that the spectral lines with fixed can be interpreted as an electron transition from one energy level at r1 to an other energy level with r2 , making Bohr’s hypothesis plausible with the corollary that electrons do not radiate in stable orbits, only when they are in transition from r1 r2 . See Fig. 18.19 on page 401. But how is the + charge, which attracts the e , is distributed In 1909-1911 Rutherford used particles emerging from decaying nuclei and bombarded an gold foil. Found the amazing events that particles scatter backward. This indicates that a positive charge is concentrated in a small sphere thus the particle’s kinetic energy is converted into potential energy q mv2 k nucleus r 2 and it can recoil like See graph 3 on page 406. 4/13/2017 Physics 214 Spring 2016 5 Mendeleev’s periodic table can be interpreted as Z Atom = Atom contains Z proton and it is located at th the z position and Z electrons orbit around the protons. Atoms in one columns have equal number of electrons on the outer orbits. See Fig. 18.5 on page 390. 4/13/2017 Physics 214 Spring 2016 6 The basic building blocks •The basic building blocks that make up atoms are • charge mass •Proton 1.6 x 10‐19 1.672 x 10‐27kg •Neutron 0 1.675 x 10‐27kg •Electron ‐1.6 x 10‐19 9.1 x 10‐31kg •Photon 0 E = hf p = h/λ •h = Planck’s constant = 6.626 x 10‐34J.s 4/13/2017 Physics 214 Spring 2016 7 The nucleus •The nucleus was found by Rutherford in scattering charged particles from a gold foil. •He observed that occasionally the charged particle was deflected through a large angle indicating it had “hit something hard” The nucleus of any atom is composed of protons and neutrons. The protons have positive electric charge so repel each other. If they are close enough the strong force binds them together and the nucleus is stable 4/13/2017 Physics 214 Spring 2016 8 Atoms •Atoms are made up with a central nucleus of protons and neutrons surrounded by a number of electrons equal to the number of protons. • The notation we use is 2He4 •2 is the atomic number = number of protons (and electrons) •4 is the mass number = number of protons + neutrons •Note atomic mass is the actual mass of the nucleus in atomic mass units with Carbon set to be 12 units and atomic mass in general is not an integer •H2O gives the number of atoms required to make a molecule • water = 2 Hydrogen plus 1 Oxygen •In a nuclear reaction energy, charge, and atomic mass are conserved. •Atoms can decay •Atoms can join together to form new atoms or molecules •Chemistry is determined by the electrons 4/13/2017 Physics 214 Spring 2016 9 3E-05 Cloud Chamber As charged particles pass through a gas electrons are knocked out of the atom and the ions produced can act as “seeds” for a super saturated liquid to condense. This leaves a visible track of bubbles of liquid. Cosmic rays are bombarding the earth continuously and radioactive decays also produce charged particles which can be observed in a cloud chamber. If the chamber is in a magnetic field the tracks are curved The first observation of the positron (anti particle of the electron) was made in a cloud chamber 4/13/2017 Physics 214 Spring 2016 10 Isotopes •For a given number of protons there is a nucleus that is most stable for a particular number of neutrons. •Isotopes are when for the same number of protons the number of neutrons is different from the most stable configuration. •Since the number of electrons is the same the chemical properties are “identical” but the nucleus can be unstable. •The larger the difference between ideal and the isotope the more unstable the nucleus becomes. •Nuclei have been made artificially that do not exist in nature. 4/13/2017 Physics 214 Spring 2016 11 Lecture 32 April 14. 2017. Hydrogen Discharge Tube and Emission of Discrete Wavelengths Description of the discrete Hydrogen Emission Spectrum by the Balmer (1884) – Rydberg –Ritz formula (1908) Cathode Ray Tube and Thomson's discovery of electrons, particles and photons (1897) Cathode Ray Tube and Röntgen’s discovery of X-ray photons Black Body radiation and Max Planck’s quantum hypothesis: E h Photo Electric Effect and its interpretation by Einstein 4/7/2016 Physics 214 Spring 2017 1 Bohr’s hypothesis of the Hydrogen Atom a.) Electron orbits around proton in its Coulomb field like the solar system b.) Only certain stable orbits are permitted c.) Photons are emitted or absorbed in the transitions between these stable orbits d.) Electrons do not radiate when move in stable orbits Periodic Table and Rutherford’s Experiment Nuclear structure and radioactivity 4/7/2016 Physics 214 Spring 2017 2 Improvements over Guericke's (Mayor of Magdeburg 1654) vacuum pump and Volta-Galvani’s battery, resulted in Hydrogen gas discharge tube and in high vacuum and high voltage cathode ray tube. The Hydrogen discharge tube produced a remarkable four discrete line spectrum: a red, a blue and two violet lines. See Fig. 18.17 on page 399. Balmer (1884) – Rydberg – Ritz (1908) described the above observation by the equation: 1 R( 1 1 ) 2 2 n m Where R is called the Rydberg constant and n, m are integers. This formula was the forerunner of quantum rather then continuum physics. 4/7/2016 Physics 214 Spring 2017 3 4/7/2016 Physics 214 Spring 2017 4 Upon heating the cathode of the cathode ray tube (See Fig. 18.6 on page 391) three kind of beams (1897) emerged: particles particles particles Which we identify: particle with Helium nucleus particle with the electron of Benjamin Franklin by Thomson in 1897. See Fig. 18.7 and 18.8 on page 393. particle with high energy photon by Röntgen. See Fig. 18.10 and 18.11 on page 394. 4/7/2016 Physics 214 Spring 2017 5 4/7/2016 Physics 214 Spring 2017 6 4/7/2016 Physics 214 Spring 2017 7 4/7/2016 Physics 214 Spring 2017 8 Max Planck painted black the inside of a closed cube and drilled a small hole on one of its side and measured the distribution of of the emitted (black body) radiation. (See Fig. 18.18 on page 400) Max Planck could explain the observed spectral distribution of the black body radiation only if he assumed that the relation between the energy and frequency of the radiation is E h Using this relation Einstein could explain the Photo Electric Effect, the emission of bound electron from metals Ee h and obtain the Nobel prize. 4/7/2016 Physics 214 Spring 2017 9 4/7/2016 Physics 214 Spring 2017 10 Planck’s relation and its interpretation by Einstein suggests that the discrete spectral lines of H 2 gas ( See Fig. 18.17 on page 399) with fixed can be interpreted as an electron transition from one stable orbit with energy level E1 ( r1 ) with radius r1 to another stable orbit with energy level E2 (r2 ) with radius r2 . To make Bohr’s hypothesis possible he added the corollary that electrons do not radiate in stable orbits, only when they are in transition from r1 r2 . See Fig. 18.19 on page 401. But how is the + charge, which attracts the e , is distributed In 1909-1911 Rutherford used particles emerging from decaying nuclei and bombarded a gold foil. He found amazing events where particles scatter backward. This indicates that a positive charge is concentrated in a small sphere thus the particle’s kinetic energy is converted into potential energy, stops and recoils. q mv2 k nucleus r 2 See graph 3 on page 406. 4/7/2016 Physics 214 Spring 2017 11 4/7/2016 Physics 214 Spring 2017 12 4/7/2016 Physics 214 Spring 2017 13 Mendeleev’s periodic table can be interpreted as N Atom = Atom z contains Z proton and N nucleons (protons + neutrons) it is located at th the z position in the periodic table and Z electrons orbit around the protons. Atoms in one columns have equal number of electrons on the outer orbits. See Fig. 18.5 on page 390. 4/7/2016 Physics 214 Spring 2017 14 4/7/2016 Physics 214 Spring 2017 15 The basic building blocks •The basic building blocks that make up atoms are • charge mass •Proton 1.6 x 10‐19 1.672 x 10‐27kg=938.27MeV •Neutron 0 1.675 x 10‐27kg=939.56MeV •Electron ‐1.6 x 10‐19 9.1 x 10‐31kg=0.51MeV •Photon 0 E = hf p = h/λ •h = Planck’s constant = 6.626 x 10‐34J.s 4/7/2016 Physics 214 Spring 2017 16 The nucleus •The nucleus was found by Rutherford in scattering charged particles from a gold foil. •He observed that occasionally the charged particle was deflected through a large angle indicating it had “hit something hard” The nucleus of any atom is composed of protons and neutrons. The protons have positive electric charge so repel each other. If they are close enough the strong force binds them together and the nucleus is stable 4/7/2016 Physics 214 Spring 2017 17 Atoms •Atoms are made up with a central nucleus of protons and neutrons surrounded by a number of electrons equal to the number of protons. • The notation we use is 2He4 •2 is the atomic number = number of protons (and electrons) •4 is the mass number = number of protons + neutrons •Note atomic mass is the actual mass of the nucleus in atomic mass units with Carbon set to be 12 units and atomic mass in general is not an integer •H2O gives the number of atoms required to make a molecule • water = 2 Hydrogen plus 1 Oxygen •In a nuclear reaction energy, charge, and atomic mass are conserved. •Atoms can decay •Atoms can join together to form new atoms or molecules •Chemistry is determined by the electrons 4/7/2016 Physics 214 Spring 2017 18 3E-05 Cloud Chamber As charged particles pass through a gas electrons are knocked out of the atom and the ions produced can act as “seeds” for a super saturated liquid to condense. This leaves a visible track of bubbles of liquid. Cosmic rays are bombarding the earth continuously and radioactive decays also produce charged particles which can be observed in a cloud chamber. If the chamber is in a magnetic field the tracks are curved The first observation of the positron (anti particle of the electron) was made in a cloud chamber 4/7/2016 Physics 214 Spring 2017 19 Isotopes •For a given number of protons there is a nucleus that is most stable for a particular number of neutrons. •Isotopes are when for the same number of protons the number of neutrons is different from the most stable configuration. •Since the number of electrons is the same the chemical properties are “identical” but the nucleus can be unstable. •The larger the difference between ideal and the isotope the more unstable the nucleus becomes. •Nuclei have been made artificially that do not exist in nature. 4/7/2016 Physics 214 Spring 2017 20 Radioactive decay •The general rule is that if a lower energy configuration exists for the same set of particles then they will try to change into that configuration. Each radioactive element has a characteristic half life, that is the time for half the sample to decay. Radioactive elements are clocks which tick at a specific rate. The amount remaining after N half lives is ½ x ½ x ½ ……….. Half lives vary from billions of years to a fraction of a second. Those in the range of greater than thousands of years are used to date objects on earth back to it’s formation 4.6 billion years ago C14 5730 years I129 1.6 million U238 4.47 billion http://www.physics.purdue.edu/class/applets/phe/lawdecay.htm 4/7/2016 Physics 214 Spring 2017 21 Types of nuclear decays A proton can change into a neutron and emit a positron (anti particle of electron) 0 e 1 Atomic number decreases by 1 mass number is the same A neutron can change into a proton and emit an electron 0 e ‐1 Atomic number increases by 1 mass number is the same A nucleus can emit an alpha particle which is 2 neutrons and 2 protons (actually a helium nucleus) 4 He 2 Atomic number decreases by 2 mass number decreases by 4 Photons can be emitted No change in Atomic number or mass number. 4/7/2016 Physics 214 Spring 2017 22 What is the daughter? •When an element decays it usually changes to a new element. •The notation we use is 3Li7 where 3 is the number of protons, called the atomic number, and 7 is the number of protons plus neutrons, called the mass number. •Any decay or nuclear reaction conserves charge and mass number. • • 4 2He + 7N14 = 8O17 + 1H1 nuclear reaction 226 = Rn222 + He4 Ra nuclear decay 88 86 2 4/7/2016 Physics 214 Spring 2017 23