CHEMISTRY 1 CHEMISTRY 1 Nuclear Chemistry Chapter 28

NUCLEAR CHEMISTRY Antoine Becquerel discovered ___________________ He accidently left uranium ore on top of photographic plates. They became fogged from the exposure. Becquerel had 2 graduate students: _______________ _______________ radioactivity Marie & Pierre Curie

_______________________- the property by which uranium gives off rays ______________________-penetrating rays emitted by a radioactive source.  In 1903, the Curies and Becquerel won Nobel prizes for this discovery. Radioactivity Radiation

Types of Radiation 1. Alpha emission -helium nuclei emitted from a radioactive source  2 protons & 2 neutrons  2 + charge  Symbol is   Don’t travel far and are not very penetrating  Stopped by a sheet of paper  Can’t penetrate skin, but dangerous if ingested  Very common with heavy nuclides He Write this

Alpha Decay (α) Lose 2 protons (+2 charge) & 2 neutrons He 4242

Examples: U  ___ + He Ra  Rn + He Th Law of conservation of mass Atomic # Mass # = # protons + # neutrons

RaRn + He Atomic # Mass #

2. Beta emission - fast moving ___________ formed by the decomposition of a neutron of an atom. The neutron breaks into a proton and an electron. The proton stays in the nucleus and the electron is ejected. (net effect: neutron changes into proton)  Write this: n  H + e electrons

 Much smaller than alpha particles  Symbol is   Charge is -1  Much more penetrating than alpha particles  Stopped by aluminum foil or thin pieces of wood C  N + e e Write this

Beta Decay (β) Lose electron (-1 charge, no mass) β 0 CN + β

3. Gamma emission - _________________ _____________ (high energy) emitted from a nucleus as it changes from an excited state to a ground energy state.  Often emitted along with  or  radiation  Symbol is   Has no mass & no charge  High energy photon U  He + Th + 2  electromagnetic radiation

 the emission of gamma rays is one way that a nucleus with excess energy (in an excited nuclear state) can relax to its ground state  Extremely penetrating, very dangerous  Stopped somewhat by several feet of concrete or several inches of lead

Gamma Emission (γ) γ 0000 No mass, no charge, loses just energy

4. Positron emission- ___________________________________  e  Antimatter  Net effect: changes proton to a neutron  Occurs when neutron/proton ratio is too small Na  e + Ne Particle with the mass of an electron but a positive charge Write this (the 0 and the +1)

Alpha radiation cannot penetrate the skin and can be blocked out by a sheet of paper, but is dangerous in the lung. Beta radiation can penetrate into the body but can be blocked out by a sheet of aluminum foil. Gamma radiation can go right through the body and requires several centimeters of lead or concrete, or a meter or so of water, to block it.

Make sure you have both of these things: Calculator Periodic Table

Nuclear Transformation (Transmutation)- ____________________________________  bombarding with alpha particles  Bombarding with neutrons N + He  O + H U + n  U Changing one element into another Write these

Fill in the blanks (not in your notes): 1. Co Ni + ____ 2. Am Np + ____ 1. Th He + ____ 2. N + ____ C + H Ra 1010 n He e

Half-life (t 1/2 ) the time required for ½ of the atoms of a radioisotope to emit radiation and decay to products the longer the half-life, the more _____________ the isotope varies from fractions of a second to millions of years stable

Examples Nitrogen-13 decays to carbon-13 with a half- life of 10 minutes. How long is 4 half lives? 4 half livesX10 min/half life= 40 min.

If you start with 2.00 g of nitrogen-13 how many grams will remain after 4 half lives? 2.00 g1.00 g0.500 g0.250 g g 4 321

Phosphorous-32 has a half-life of 14.3 yr. How many grams remain after 57.2 yr from a 4.0 g sample? 57.2 yr 14.3yr / half-life =4 half-lives 4.0 g2.0 g1.0 g0.50 g g 4

Carbon-14 dating Carbon-14 is continuously produced in the ____________ when high energy neutrons from outer space collide with nitrogen-14 in the air. N + n  C + H atmosphere

Carbon-14 combines with oxygen to form CO 2 which is incorporated into plant materials. As long as the plant or animal is alive, decaying carbon-14 is continuously replaced. After death, the carbon-14 decays at a steady rate. Carbon-14 decays to Nitrogen-14 C  e + N

The proportion of carbon-14 in the atmosphere is relatively constant. The carbon-14/carbon-12 ratio is used to identify the age of wood, cloth and other ______________ artifacts. The half-life of carbon-14 is _______________ years. Only works for organic materials Adjusted for change in % C-14 over the years organic 5730

Example If the C-14 in a fossil sample is only 1/4 what it is in living organisms, how old is the object? To have ¼ remaining, 2 half lives have passed. 2X5730 yr= 11,460 yr.

Fission - splitting a heavy nucleus into two nuclei with smaller mass numbers. used for _____________________ production of ______________causes a chain reaction (which must be controlled) 1 kg of uranium-235 is equivalent to 20,000 tons of dynamite nuclear energy n + U  Ba + Kr + 3 n neutrons

Fission – splitting of atoms. FISSION: splitting of atoms

Fission in a nuclear reactor is carefully controlled. Much of the energy is _______. This energy is used to produce _________ and subsequently, __________________. Fission in a nuclear reactor is carefully controlled. Much of the energy is _______. This energy is used to produce _________ and subsequently, __________________. A _________________(usually water) is needed. The water (or carbon) also acts as a moderator. It _____________the neutrons down so that they can be captured by the U-235 fuel. Control rods made of _______________ are present to absorb excess neutrons to slow down the reaction. They can be raised or lowered into the reactor core. heat steam electricity coolant slows cadmium

Fusion- combining two light nuclei to form a heavier, more stable nucleus stars produce their energy this way Currently __________________ are necessary in order to initiate fusion possible future energy source high temperatures 4 H + 2e  He + energy

Fusion – two nuclei combine to form a heavier nucleus. FUSION: two nuclei combine to form a heavier nuclei

Proton-proton chain reaction Fusion reaction in our Sun’s core.