Aim # 45: What is Radioactivity? H.W. # 45 Study pp. 607-612 Ans. ques. p. 629 # 1,6-9 p. 630 # 11,12a,13,14a,15c

Element Protons Neutrons He 2 2 N 7 7 O 8 8 Ne 10 10 S 16 16 Cu 29 35 Kr 36 48 Bi 83 126 U 92 146 Is there a trend in the relationship between the number of protons and the number of neutrons in an atom? Given the stability of a nucleus, is there anything that seems peculiar about that? Why does H have no neutrons?

I Radioactivity- the spontaneous breakdown of atomic nuclei accompanied by the release of sub-atomic particles and energy. All isotopes of elements with atomic numbers greater than 83 (Bi) are radioactive (radioisotopes).

II Ernest Rutherford directed the radiation from various radioisotopes through an electric field. What conclusion would you draw about radioactive emissions based upon the results? There are 3 basic types. Alpha particles- deflect toward the negative electrode. Beta particles- deflect toward the positive electrode. Gamma Rays- are not deflected.

Alpha (α) Helium nucleus 2+ 4 amu single sheet of paper Beta (β) Type of Radiation Composition Charge Mass Able to be stopped by Alpha (α) Helium nucleus 2+ 4 amu single sheet of paper Beta (β) electron 1- 1/1836 amu thin sheet of aluminum Gamma (γ) radiation (energy) -------- several cm of lead

Identify X along with its mass number and atomic number. Ans. 234Th 90 III A. When an alpha particle is emitted as a result of nuclear disintegration, the reaction is called alpha decay. e.g. 226Ra → 222Rn + 4He 88 86 2 Problem: 238U → ?X + 4He 92 ? 2 Identify X along with its mass number and atomic number. Ans. 234Th 90

B. When an atom emits a beta particle (beta decay), When an atom emits an alpha particle, its at. no. decreases by 2 and its mass no. decreases by 4. A NEW SUBSTANCE IS PRODUCED! B. When an atom emits a beta particle (beta decay), its at. no. increases by 1 and its mass number remains the same. Where do the new proton and electron come from? Note: The electron (beta particle) comes from the nucleus! 1n → 1H + 0e 0 1 -1 The difference between a beta particle and an electron is their source within the atom.

Problem: 234Pa → X + 0e 91 -1 Identify X , using the proper notation Ans: 234U 92 Emissions of beta particles are often accompanied by the emission of gamma rays. .

IV Positron Decay- a positron has the mass of an electron, buy the charge of a proton. Positron decay occurs when a nucleus has too few neutrons relative to the number of protons 1p → 1n + 0e 1 0 +1 β+ is another symbol for a positron. at. no. decreases by 1, at. Mass remains the same. e.g. 8B → 8Be + 0e 5 4 +1 Problem: 15O → X + 0e 8 +1 Ans: 15N 7

Identify each unknown X 230Th 90 222Rn 86 0e -1 4He 2 234U → X + 4He 92 2 X → 218Po + 4He 84 2 210Pb → 206Bi + X 84 82 210Po → 206Pb + X 84 82