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Should the existence of nuclear waste restrain us in our development of nuclear energy? Nuclear Chemistry Notes 11/3 & 11/4 E=mc2 Nuclear Fission Nuclear Stability Radioactivity Around Us Radioactive Decay Half Life Scale Model of the Atom Atoms are mostly empty space The diameter of the atom is 100,000 times that of its nucleus 25 km The emptiness of the atom is key to understanding the relationship of the atom to its nucleus Which system gives the atom its size? Which system gives the atom its mass? • In most cases, regard the two systems as – Separate – Independent • Mass of a proton or a neutron is about 2000 x the mass of an electron The emptiness of the atom is key to understanding the relationship of the atom to its nucleus Which do you think requires less energy to remove from the atom? A particle of the nucleus, or an electron? Why do you think that? • Particles in the nucleus are tightly locked in • The energies available in the nucleus are much greater than those available among the electrons The enormous energy we can get from the nucleus follows from the equivalence of mass and energy Einstein’s formula tells us that a given amountSpeed of mass can be of light is a very big number! converted into amount of 8 m/sec 3 xa 10specific energy in any form, and vice versa. http://www.seanpaune.com/wp-content/uploads/2011/03/Fukushimanuclear-power-plant.gif Empty Space, Explosive Energy! A nuclear reactor can transform fully 20% of the mass of a proton into energy in each reaction E=mc2 Nuclear Fission Nuclear Stability Radioactivity Around Us Radioactive Decay Half Life Chart of the Isotopes Number Protons vs. Number Neutrons Green dot = stable Yellow dot = unstable Chart of the Isotopes #protons vs. #neutrons Where are the green dots when #P about the same as #N? – Lighter elements (atomic #<20) are stable when #P and #N are about equal Green dot = stable Yellow dot = unstable • What happens to the ratio P:N as the atomic # increases? – Atom needs MORE N than P to maintain stability – ALL elements with atomic # >83 are unstable (radioactive) Nuclear Chemistry Radioactivity • Spontaneous release of energy from an unstable nucleus Radiation • Energy released when an unstable atom spontaneously decays Types of Radiation – alpha decay • Heavy, positively charged particles • a stream of helium atoms that have no electrons • Symbols: An unstable nucleus ejects a particle made up of 2 protons and 2 neutrons Types of Radiation – beta decay • Light weight, negatively charged particles • a high energy stream of electrons • Symbols: A neutron splits into a proton, an electron, and an antineutrino Types of Radiation - gamma • Pure electromagnetic energy • *Does not change the element! • Has no mass or charge • Symbol: Balanced Nuclear Equations • Mass and charge must be the same on both sides • We’ll do the first four together • You will have 8-10 minutes to work the last 6 at your table Nuclear Decay Do: Complete #4 through 10 Put: Write answers on the worksheet Finish By: 5 min. total When Done: Wait quietly until the timer rings Be prepared to share at the document camera How is the process of half-life related to radioactive decay? Half-life… •The amount of time required for ½ of a radioactive substance to decay away Decay Series of U-238 • Has a long half-life— 4.5 x 109 years • Decays through a series of unstable isotopes • Radon (Rn) gas is one of the intermediate decay products Half-life of Radioactive Isotopes • Calculate how many half-lives have transpired? • Plug and chug Half Life Do: Complete #3 through 6 Put: Write answers on the worksheet Finish By: 10 min. total When Done: Wait quietly until the timer rings Be prepared to share at the document camera Nuclear Fission • Fission is the splitting of a large, unstable atom into 2 or more smaller atoms [see p. 888 Fig.25.11] • Fission is the process found in atomic bombs and nuclear reactors Fusion Reactions http://en.wikipedia.org/wiki/Nuclear_fusion • Two or more smaller atoms are combined into a larger atom [See page 891—Fig. 25.14] • Stars produce energy through fusion The Sun is a main-sequence star, and thus generates its energy by nuclear fusion ofhydrogen nuclei into helium. In its core, the Sun fuses 620 million metric tons of hydrogen each second. E=mc2 Nuclear Fission Nuclear Stability Radioactivity Around Us Radioactive Decay Half Life Murkiest Point Card Do: What questions do you still have about radioactivity and the unstable nucleus? Put: Write your name—Period # and write 1 or 2 of the most pressing question(s) on a notecard (on front bench) Finish By: Remainder of class period When Done: turn it into the basket; if there is more than 5 minutes of class time remaining, work on chemistry or discuss chemistry at your table