Nuclear Chemistry Chapter 28

Introduction to Nuclear Chemistry Nuclear chemistry is the study of the structure of and the they undergo. atomic nuclei changes

Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons Associated with small energy changes Associated with large energy changes Reaction rate influenced by temperature, particle size, concentration, etc. Reaction rate is not influenced by temperature, particle size, concentration, etc.

Radioactivity – some key terms Isotopes – atoms of the same element with different numbers of neutrons Radioisotopes – isotopes of atoms with unstable nuclei (too many or few neutrons) Radioactive decay – when unstable nuclei lose energy by emitting radiation to attain more stable atomic configurations (spontaneous process)

Review of Atomic Structure Nucleus Electrons 99.9% of the mass but 1/10,000 the size of the atom 0.01% of the mass Composed of protons (p+) and neutrons (n0) Composed of electrons (e-) Positively charged Negatively charged Strong nuclear force (holds the nucleus together) Weak electrostatic force (because they are charged negatively)

mass # atomic # Chemical Symbols C A nuclear symbol looks like… To find the number of neutrons, subtract the atomic number from the mass number. mass # 14 C atomic # 6

Nuclear Stability An Isotope is completely stable if the nucleus will not spontaneously decompose. Elements with atomic numbers 1 to 20 are very stable. A 1:1 ratio of protons : neutrons (p+ : n0) makes an isotope very stable Example: Carbon – 12 has 6 protons and 6 neutrons

Nuclear Stability Elements with atomic numbers 21 to 82 are marginally stable. A 1 : 1.5 ratio of protons : neutrons (p+ : n0) Example: Mercury – 200 has 80 protons and 120 neutrons

Nuclear Stability Elements with atomic numbers > 82 are unstable and radioactive. Isotopes with greater than 1.5 neutrons per 1 proton are unstable or radioactive Examples: Uranium and Plutonium

Transmutation Transmutation is the conversion of one atom of one element to an atom of a different element. Alpha and beta decay cause this to occur.

α 4 mass 4 atomic 2 He Alpha Decay +2 protons Alpha decay – emission of an alpha particle ( ), denoted by the symbol , because an α has 2 protons and 2 neutrons, just like the He nucleus. Charge is because of the 2 . Mass of alpha particle is amu. Alpha decay causes the number to decrease by and the number to decrease by . This can be shielded by a sheet of paper He 4 2 +2 protons 4 mass 4 atomic 2

Alpha Decay Example 1: Write the nuclear equation for the radioactive decay of polonium – 210 by alpha emission. Step 3: Write the alpha particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 210 Po 84 206 Pb 4 He 2 82 Atomic #

Alpha Decay Example 2: Write the nuclear equation for the radioactive decay of radium – 226 by alpha emission. Step 3: Write the alpha particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 226 Ra 88 222 Rn 4 He 2 86 Atomic #

β e- e electron -1 electron no mass 1 Beta decay atomic Beta decay – emission of a beta particle ( ), a fast moving , denoted by the symbol or . β has insignificant mass ( ) and the charge is because it’s an . This occurs as a neutron changes into a proton by emitting the negatively charged beta particle Beta decay causes change in number and causes the number to increase by . These can be shielded by metal foil. e- electron e -1 -1 electron no mass atomic 1

C e N Beta Decay 14 6 14 -1 7 Step 3: Write the beta particle. Example 1: Write the nuclear equation for the radioactive decay of carbon – 14 by beta emission. Step 3: Write the beta particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 14 C 6 14 e -1 N 7 Atomic #

Zr e Nb Beta Decay 97 40 97 -1 41 Step 3: Write the beta particle. Example 2: Write the nuclear equation for the radioactive decay of zirconium – 97 by beta decay. Step 3: Write the beta particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 97 Zr 40 97 e -1 Nb 41 Atomic #

electromagnetic γ no mass atomic always no omitted Gamma decay Gamma rays – high-energy radiation, denoted by the symbol . γ has no mass ( ) and no charge ( ). Thus, it causes change in or numbers. Gamma rays almost accompany alpha and beta radiation. However, since there is effect on mass number or atomic number, they are usually from nuclear equations. These can be shielded by lead or concrete. γ no mass atomic always no omitted

Type of Radioactive Decay Review Type of Radioactive Decay Particle Emitted Change in Mass # Change in Atomic # Alpha α He -4 -2 Beta β e +1 Gamma γ 4 2 -1