Unit 3: Part 2 of the Atom Nuclear Chemistry I. The Nucleus (p. 701 – 704 in Class Modern Chemistry Text) II III IV

A. Mass Defect Difference between the mass of an atom and the mass of its individual particles. 4.00260 amu 4.03298 amu

Important Values 1.007276 amu = mass of 1 p+ 1.008665 amu = mass of 1 n0 0.0005486 amu = mass of 1 e- 1.6605 x 10-27 kg = 1 amu Speed of light (c) = 3.00 x 108 m/s

A. Mass Defect Calculated Helium-4 nuclide: Atomic Mass = 4.002602 amu How do we calculate its mass defect? Find the mass of the subatomic particles 1st 2 p+ = (2 x 1.007276 amu) = 2.014552 amu 2 n0 = (2 x 1.008665 amu) = 2.017330 amu 2 e- = (2 x 0.0005486 amu) = 0.001097 amu Total combined mass = 4.032979 amu

A. Mass Defect Calculated How do we calculate its mass defect? Total combined mass - Atomic mass = mass defect 4.032979 amu – 4.002602 amu = 0.030377 amu The measured mass is 0.030377 amu less then the total mass we calculated for the combined subatomic particles This is the mass defect for the helium-4 nuclide

B. Nuclear Binding Energy Energy released when a nucleus is formed from nucleons. High binding energy = stable nucleus. E = mc2 E: energy (J) m: mass defect (kg) c: speed of light (3.00×108 m/s)

Converting mass defect to Nuclear Binding Energy We will use the helium-4 nuclide again Convert mass defect from amu to kg 0.030377amu 1.6605 x 10-27 kg 1 amu E = mc2 = (5.0441x10-29 kg)(3.00 x 108 m/s)2 = 4.54 x 10-12 J This is the energy required to hold the nucleus together = 5.0441x10-29 kg

Practice Problem Calculate the nuclear binding energy of a sulfur-32 atom. The measured atomic mass of this nuclide is 31.972070 amu. Answer = 4.36 x 10-11 J

B. Nuclear Binding Energy Unstable nuclides are radioactive and undergo radioactive decay.

Nuclear Reactions In equations representing nuclear reactions, the total of the atomic numbers and the total of the mass numbers must be equal on both sides of the equation. Here is an example Br + He  C + n  Notice there has been a transmutation

Quiz A process in which a very heavy nucleus splits into more-stable nuclei of intermediate mass is called:   radioactive decay   nuclear fusion   a chain reaction   nuclear fission   radiocarbon dating

Quiz Very large nuclei tend to be unstable because of the: repulsive forces between protons attraction of protons for neutrons repulsive forces between neutrons attraction of electrons for the positively charged nucleus

Quiz Compared to chemical reactions, nuclear reactions produce:  proportionally far less energy  proportionally far more energy  more vegetables  fewer changes in the nucleus

Online practice quiz for you to try http://www.sciencegeek.net/Chemistry/taters/Unit1NuclearChemistry.htm Online practice quiz for you to try Using the Modern Chemistry text try the section review questions on page 704.

VOCABULARY Nucleons: the protons and neutrons in the nucleus of an atom Nuclide: an atom in nuclear chemistry is referred to as one of these Mass defect: the difference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons Nuclear binding energy: the energy released when a nucleus is formed from nucleons. It is calculated using E = mc2 Nuclear reaction: a reaction that changes the nucleus of an atom transmutation: a change in the identity of a nucleus as a result of a change in the number of protons