The Atom (Power Point 10) http://www.pond5.com/stock-footage/68580/atom5.html

Student Learning Objectives Describe the structure of the atom and the resultant changes through fission, fusion, and radioactive decay. Characterize the atom Analyze the quantum nature of the atom Analyze radioactive decay processes Differentiate between nuclear fission & fusion

What are the defining properties of regular atoms? Regular, neutral atoms have an equal number of electrons, protons, and neutrons. What makes each atom unique is the number of protons.

Practice Where is most of the mass in an atom? What contributes most to the size of an atom? What is an ion? Nucleus Electron orbits Electric force – electrons repelling Electrons can be lost or gained

More Practice Use your knowledge of what an ion is, to determine what an isotope is. Since atoms are mostly empty space, why can’t we walk through walls?

What is meant by the wave-particle duality? Quantum theory predicts that objects emit individual packets of energy (photons). Sometimes light behaves as a wave (wavelengths) and sometimes light behaves as a particle (photons). Wave-Particle Duality Half way down link page

Wave-Particle Duality All subatomic particles exhibit wave-particle duality. Bohr postulated the electron is a particle orbiting the nucleus in specific orbits. de Broglie contended that the behavior of electrons is explained only if the electron is considered as a standing wave. Image Credit: Opentextbc.ca

Effects of Electron Standing Waves

de Broglie Wavelength ldB = h . mv Every particle of mass creates a standing wave when in motion. ldB = h . mv

Practice How does the de Broglie wavelength of a person compare to the de Broglie wavelength of an electron? Can we really know exactly where the electron is? Explain. Mass Speed Electron (hydrogen) 9.1 x 10−31 kg 2.2 x 106 m/s Person (walking) 70 kg 1.4 m/s

Heisenberg Uncertainty Principle Heisenberg’s Principle: the position and the velocity of an object cannot both be measured exactly, at the same time. Because of its wave character, a particle’s trajectory and destination cannot be precisely predicted for each particle individually. Electron Probability Regions

How do atoms emit and absorb light? Each atom has its own unique pattern of allowed orbits, based on the number of protons. When electrons change orbits, light is emitted or absorbed. Image Credit: Wikipedia

Image Credit: Openstax Energy States The farther an electron is from the nucleus, the higher its energy level. Ground State: electrons occupy lowest energy levels Excited State: electrons in added energy levels Image Credit: Openstax

Each type of atom emits/absorbs its own specific pattern of photons. Atomic Spectrum Image Credit: Openstax

Photon Energy DEn = E(photon) E = hc l E = hn Each photon has a particular energy, based on the quantum jump. DEn = E(photon) Each color of light has a particular energy per photon. h = 6.63 x 10-34 Js E = hc l E = hn

Practice What is the energy of a photon that results from the 4  2 transition in the hydrogen atom? What is this energy in Joules? 1 ev = 1.6 x 10−19 Joules Hydrogen Orbit eV n = 1 8 n = 2 15 n = 3 30 n = 4 80

More Practice What is the energy of one yellow photon (l = 517 nm) from the Sun? How does the energy of one photon from the Sun compare to the total energy output of the Sun (4 x 1026 Watts)? Image Credit; NASA

How do we know the number of particles? Atomic number = number of protons Atomic Mass = mass in amu or grams Mass number = protons + neutrons 178O−2

Practice Classify each atom. Is it an ion? Is it an isotope? 32He 136C 3417Cl−1 5226Fe 63Li+1

How is the nucleus held together? The protons and neutrons in the core of an atom are held together by the strong nuclear force. Diameter < 10-15 m The strong nuclear force balances the electric force in a stable atom. FN FE

Nuclear Force vs. Electric Force Strong Nuclear Force Electric Force Attraction Repulsion Protons & Neutrons Protons Range < 10-15 m Range > 10-15 m

Practice Would a helium (He) atom or a bismuth (Bi) atom tend to be more unstable? Analyze the possible stability of a 32He atom.

60+ radioactive elements found in nature What is radioactivity? Radioactivity is the transformation of an unstable atom into a different type of atom. 60+ radioactive elements found in nature There are 3 general sources of radioactivity. Earth Cosmic Rays Human Produced

Radioactive Decay processes Atoms radioactively decay by emitting high energy particles. If the decay particle comes from the nucleus, then the atomic number changes. a decay (nucleus) b decay (nucleus) g decay (D e− orbit)

Can cause damage on the surface of matter Alpha Decay Alpha radiation (a) is the emission of two protons as a helium (He+) particle. The positively charged particle leaves the nucleus. Can cause damage on the surface of matter Image Credit: JAHSCHem - Wikispaces

Can penetrate through several millimeters of matter Beta Decay Beta radiation (b) is the emission of an electron (e−) with negative charge. A neutron splits, emits the electron, and leaves a proton. Can penetrate through several millimeters of matter 83Li 84Be e− Creative Commons Image

Can pass through all types of matter Gamma ray A Gamma ray (g) is a high energy photon that is emitted. An electron jumps from a very high orbit to a lower orbit. Can pass through all types of matter Excited Atom Same Nucleus Gamma Ray released Creative Commons Image

Creative Commons Image

The Rules Unstable Condition Name Symbol The Rules 83+ Protons Alpha +2 a D(Mass #) = – 4 D(Atomic #) = – 2 Neutron/Proton Ratio Beta e– –1 b D(Mass #) = – 0 D(Atomic #) = + 1 Excited Nucleus Gamma photon g No Change

Practice Answer the listed questions for each nuclear reaction. Is the atom an isotope? What makes it unstable? What is the resulting atom, X? 22688Ra  X + e− 22688Ra  X + a 22286Rn  X + 42He 146C  X + b 3618Ar  X + g

What does the half-life of an element indicate? Half-life is the time it takes for one half of an unstable substance to decay into a different substance. The age of a sample can be determined from the number of half-life’s that have occurred. Isotope Half Life 156C 2.449 seconds 146C 5,730 years

Practice An isotope of radium (Ra) has a half-life of 1620 years. If 1000 grams were placed in a barrel, how much of the material in the barrel would be radium after 6480 years? 22589Ac (Actinium) has a half-life of 10.0 days. How many days would it take to decrease the original amount placed in a barrel to 1/64th of the original amount?

More Practice Caffeine has a half-life of 6 hours. If you drink an 8 oz (95 mg) cup of coffee, how long will it take for there be less than 12 milligrams remaining in your body? A can of Mountain Dew has 56 mg of caffeine. How long would it take to have less than 12 milligrams of caffeine in your body after finishing this drink?

Carbon Dating Carbon dating is the process of using the known half-life of carbon-14 to determine age of a sample. Living plants and animals take in CO2 (Carbon-14) Carbon-14 is a radioactive isotope The half-life of carbon-14 is 5,730 years 146C  147N + b

Practice The half-life of carbon-14 is 5,730 years. How old are the wood samples? Sample has 1/2 the carbon-14 as a living tree Sample has 1/4 the carbon-14 as a living tree Sample has 1/32 the carbon-14 as a living tree How do we know that the relative abundance of carbon-14 has been consistent for the last 50,000 years? Would this affect carbon dates of samples?

What is Nuclear Fission? Nuclear fission is the splitting apart of a nucleus. Electric force wins Nucleus flies apart Huge amounts of energy released Nuclear fission is used in atomic bombs and nuclear reactors. Atomic bombs produce a chain reaction. Nuclear reactors control the rate of fission.

Uranium Uranium fission yields 2.5 Million times more energy per gram than coal burning. Creative Commons Image

Question Nuclear energy is a clean fuel. It does not pollute the atmosphere. What reasons may people have for not wanting to utilize nuclear energy? Diablo Canyons Nuclear Power Plant California

Proton-Proton Chain E = mc2 Hydrogen nuclei are forced together into helium. Mass becomes energy. E = mc2

1 Second In The Sun 1038 Reactions 600 Billion kg H  He 4 Billion kg Mass  Energy 4 x 1026 Watts Image Credit: NASA

Practice Compare and contrast nuclear fission and fusion. Use the atomic mass to determine the amount of mass lost from the Sun in each PPC reaction. How much energy would result from the nuclear fusion of a 5 gram grape?

Radiation Radiation is energy. Decay particles may ionize and alter cells. On average, Americans receive a radiation dose of about 0.62 rem (620 mrem) each year.

Some Common Radiation Sources Dentist x-ray 1.5 mrems Food 39 mrems Electronics 11 mrems Tobacco 1,300 – 9,000 mrems https://xkcd.com/radiation/