Nuclear Chemistry and Radioactivity CHAPTER 20 Nuclear Chemistry and Radioactivity 20.2 Nuclear Reactions: Radioactivity

Nuclear reactions create new elements from other elements electrons protons neutrons Chemical reactions rearrange elements into new compounds, leaving the elements unchanged Nuclear reactions create new elements from other elements Nuclear equations Chemical equations

A chemical reaction rearranges atoms to form new compounds: 4Fe(s) + 3O2(g) → 2Fe2O3(s) rust

A chemical reaction rearranges atoms to form new compounds: 4Fe(s) + 3O2(g) → 2Fe2O3(s) A nuclear reaction can 1) change one element into a new element: 2) change one isotope into another isotope of the same element:

Nuclear reactions Nuclear reactions involve much more energy than chemical reactions Nuclear reactions involve the strong nuclear force, the strongest force in the universe A nuclear reaction can 1) change one element into a new element: 2) change one isotope into another isotope of the same element:

Nuclear reactions Decay reactions Fission reactions There are two main types of nuclear reactions Decay reactions Alpha particle A nucleus spontaneously disintegrates by emitting particles Fission reactions Note that the book refers to fission reactions as bombardment reactions A nucleus is broken into two or more large pieces

Decay reactions Decay reactions 1) Alpha (a) decay 2) Beta (b) decay Four most common types of nuclear decay: Decay reactions Alpha particle A nucleus spontaneously disintegrates by emitting particles 1) Alpha (a) decay 2) Beta (b) decay 3) Gamma (g) decay 4) Positron (b+) emission

Isotopes that undergo spontaneous nuclear reactions are said to be radioactive. Decay reactions Alpha particle A nucleus spontaneously disintegrates by emitting particles radioactivity: a process by which the nucleus of an atom spontaneously changes itself by emitting particles or energy.

Intensity of radiation Radiation can be dangerous because it has high enough energy to break bonds in molecules. How do we measure the intensity of radiation?

Intensity of radiation The farther we are from a source, the the amount of radiation exposure. smaller larger

Intensity of radiation The farther we are from a source, the the amount of radiation exposure. smaller larger

intensity of radiation: the amount of energy that flows per unit area per time

Inverse square law: squared value inverse square law: a law that states that the intensity of radiation emitted from a point source decreases inversely over the square of the distance.

Distance changes by a factor of 2 Inverse square law Distance changes by a factor of 2 How does the intensity compare if you stand twice as far from a radiation source?

Distance changes by a factor of 2 Inverse square law Distance changes by a factor of 2

Distance changes by a factor of 2 Inverse square law Distance changes by a factor of 2 Intensity changes by a factor of 1/4 = 1/22

Inverse square law inverse square When the distance changes by a factor of 2, the intensity changes by a factor of 1/22 = 1/4 When the distance changes by a factor of 10, the intensity changes by a factor of 1/102 = 1/100 inverse square

Decay reactions Decay reactions 1) Alpha (a) decay 2) Beta (b) decay A nucleus spontaneously disintegrates Four most common types of nuclear decay: 1) Alpha (a) decay 2) Beta (b) decay 3) Gamma (g) decay 4) Positron (b+) emission

Alpha decay Alpha decay: a nucleus emits a helium nucleus Parent nuclide Daughter nuclide He-4 nucleus (a particle)

Alpha decay a particles are very large and cannot penetrate matter very well. a particle Remember Rutherford’s experiment: Most alpha particles went through the gold sheet. Nuclei in the gold sheet caused alpha particles to bounce off in new directions.

Alpha decay a particles are very large and cannot penetrate matter very well. a particle Normally a particles cannot go through skin. However, if you eat something containing an a emitter, then the a particles can hit internal organs and cause damage.

Alpha decay Write the complete nuclear equation for the a decay of the radium isotope .

Alpha decay Write the complete nuclear equation for the a decay of the radium isotope . Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to

Alpha decay Write the complete nuclear equation for the a decay of the radium isotope . Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 222. By balancing the atomic number, we obtain Z = 86.

Alpha decay Write the complete nuclear equation for the a decay of the radium isotope . Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 222. By balancing the atomic number, we obtain Z = 86. Second, look at the periodic table to determine the identity of the unknown daughter element. Since the atomic number is 86, the daughter nuclide is radon (Rn).

Alpha decay Write the complete nuclear equation for the a decay of the radium isotope . Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 222. By balancing the atomic number, we obtain Z = 86. Second, look at the periodic table to determine the identity of the unknown daughter element. Since the atomic number is 86, the daughter nuclide is radon (Rn). Answer: The complete a decay equation is

Decay reactions Decay reactions 1) Alpha (a) decay 2) Beta (b) decay A nucleus spontaneously disintegrates Four most common types of nuclear decay: 1) Alpha (a) decay 2) Beta (b) decay 3) Gamma (g) decay 4) Positron (b+) emission

Beta decay Beta decay: an unstable nucleus releases an electron and converts a neutron into a proton. Parent nuclide Daughter nuclide b particle

Beta decay Beta decay: an unstable nucleus releases an electron and converts a neutron into a proton. Parent nuclide Daughter nuclide b particle Charge goes from 0 to +1

Beta decay Beta decay: an unstable nucleus releases an electron and converts a neutron into a proton. Beta decay: an unstable nucleus releases an electron Parent nuclide Daughter nuclide b particle 6 protons 7 protons balanced equation

Alpha decay Write the complete nuclear equation for the b decay of the radium isotope .

Alpha decay Write the complete nuclear equation for the b decay of the radium isotope . Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to

Alpha decay Write the complete nuclear equation for the b decay of the radium isotope . Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 228. By balancing the atomic number, we obtain 88 = Z – 1 or Z = 89.

Alpha decay Write the complete nuclear equation for the b decay of the radium isotope . Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 228. By balancing the atomic number, we obtain 88 = Z – 1 or Z = 89. Second, look at the periodic table to determine the identity of the unknown daughter element. Since the atomic number is 89, the daughter nuclide is actinium (Ac).

Alpha decay Write the complete nuclear equation for the b decay of the radium isotope . Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 228. By balancing the atomic number, we obtain 88 = Z – 1 or Z = 89. Second, look at the periodic table to determine the identity of the unknown daughter element. Since the atomic number is 89, the daughter nuclide is actinium (Ac). Answer: The complete a decay equation is

Decay reactions Decay reactions 1) Alpha (a) decay 2) Beta (b) decay A nucleus spontaneously disintegrates Four most common types of nuclear decay: 1) Alpha (a) decay 2) Beta (b) decay 3) Gamma (g) decay 4) Positron (b+) emission

Gamma decay Gamma decay: a nucleus releases electromagnetic energy but the isotope remains the same.

Gamma decay Gamma decay: a nucleus releases electromagnetic energy but the isotope remains the same. Gamma radiation has high enough energy to break apart other atoms, but can be stopped by a thick shielding material made of lead or concrete.

Decay reactions Decay reactions 1) Alpha (a) decay 2) Beta (b) decay A nucleus spontaneously disintegrates Four most common types of nuclear decay: 1) Alpha (a) decay 2) Beta (b) decay 3) Gamma (g) decay 4) Positron (b+) emission

Positron emission Positron emission: a nucleus releases a positron and converts a proton into a neutron. A positron is a particle that has the same mass as an electron and has a positive charge

Determine the type of decay for the following reactions:

Determine the type of decay for the following reactions: Asked: Unknowns X1 and X2 Given: Mass and atomic numbers of the parent and daughter nuclides.

Determine the type of decay for the following reactions: Asked: Unknowns X1 and X2 Given: Mass and atomic numbers of the parent and daughter nuclides. Solve: Balance the atomic numbers to find Z, and mass numbers to find A: For reaction 1: 234 = 234 + A1, so A1 = 0; 90 = 90 + Z1, so Z1 = 0.

Determine the type of decay for the following reactions: Asked: Unknowns X1 and X2 Given: Mass and atomic numbers of the parent and daughter nuclides. Solve: Balance the atomic numbers to find Z, and mass numbers to find A: For reaction 1: 234 = 234 + A1, so A1 = 0; 90 = 90 + Z1, so Z1 = 0. For reaction 2: 95 = 95 + A2, so A2 = 0; 43 = 42 + Z2, so Z2 = +1.

Determine the type of decay for the following reactions: Asked: Unknowns X1 and X2 Given: Mass and atomic numbers of the parent and daughter nuclides. Solve: Balance the atomic numbers to find Z, and mass numbers to find A: For reaction 1: 234 = 234 + A1, so A1 = 0; 90 = 90 + Z1, so Z1 = 0. For reaction 2: 95 = 95 + A2, so A2 = 0; 43 = 42 + Z2, so Z2 = +1. Answer: For reaction 1, , which denotes g decay, so

Determine the type of decay for the following reactions: Asked: Unknowns X1 and X2 Given: Mass and atomic numbers of the parent and daughter nuclides. Solve: Balance the atomic numbers to find Z, and mass numbers to find A: For reaction 1: 234 = 234 + A1, so A1 = 0; 90 = 90 + Z1, so Z1 = 0. For reaction 2: 95 = 95 + A2, so A2 = 0; 43 = 42 + Z2, so Z2 = +1. Answer: For reaction 1, , which denotes g decay, so For reaction 2, , which denotes positron decay, so

There are two main types of nuclear reactions Decay reactions Alpha particle A nucleus spontaneously disintegrates by emitting particles Fission reactions Note that the book refers to fission reactions as bombardment reactions A nucleus is broken into two or more large pieces

Decay reactions a decay b decay g decay positron emission A nucleus spontaneously disintegrates b decay g decay positron emission