Should the existence of nuclear waste restrain us in our development of nuclear energy? Nuclear Chemistry Notes 11/3 & 11/4

Radioactivity Around Us E=mc 2 Nuclear Stability Half Life Radioactive Decay Nuclear Fission

Scale Model of the Atom

Atoms are mostly empty space 25 km The diameter of the atom is 100,000 times that of its nucleus

The emptiness of the atom is key to understanding the relationship of the atom to its nucleus 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 Which system gives the atom its size? Which system gives the atom its mass?

The emptiness of the atom is key to understanding the relationship of the atom to its nucleus Particles in the nucleus are tightly locked in The energies available in the nucleus are much greater than those available among the electrons 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?

The enormous energy we can get from the nucleus follows from the equivalence of mass and energy Speed of light is a very big number! 3 x 10 8 m/sec Einstein’s formula tells us that a given amount of mass can be converted into a specific amount of energy in any form, and vice versa.

Empty Space, Explosive Energy! nuclear-power-plant.gif A nuclear reactor can transform fully 20% of the mass of a proton into energy in each reaction

Radioactivity Around Us E=mc 2 Nuclear Stability Half Life Radioactive Decay Nuclear Fission

Chart of the Isotopes Number Protons vs. Number Neutrons Green dot = stable Yellow dot = unstable

Chart of the Isotopes  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 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) #protons vs. #neutrons Green dot = stable Yellow dot = unstable

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: Charge or protons Mass # 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: Charge Mass # 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 10 9 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 Two or more smaller atoms are combined into a larger atom [See page 891—Fig ] 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.Sunmain-sequence starenergyhydrogenheliummetric tons

Radioactivity Around Us E=mc 2 Nuclear Stability Half Life Radioactive Decay Nuclear Fission

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