ENCHEM30 Chemistry for Engineers PDF

ENCHEM30 CHEMISTRY FOR ENGINEERS NUCLEAR CHEMISTRY AND ENERGY CHEMISTRY OF FUELS Department of Civil Engineering NU Clark ENCHEM30 NUCLEAR CHEMISTRY The study of the structure of atomic nuclei and the...

ENCHEM30 CHEMISTRY FOR ENGINEERS NUCLEAR CHEMISTRY AND ENERGY CHEMISTRY OF FUELS Department of Civil Engineering NU Clark ENCHEM30 NUCLEAR CHEMISTRY The study of the structure of atomic nuclei and the changes they undergo. As with conventional chemical reactions, a nuclear reaction is accompanied by energy changes. NUCLEAR CHEMISTRY NUCLEAR REACTIONS The “ordinary chemical reactions” discussed from the previous lessons involve changes in the outer electronic structures of atoms or molecules. In contrast, nuclear reactions result from the changes taking place within the atomic nuclei. ENCHEM30 ATOMIC NUCLEI The atomic nuclei are represented by symbols such as: NUCLEAR CHEMISTRY ENCHEM30 Examples: Nuclear Notation What is the isotopic notation for the isotope carbon-14? NUCLEAR CHEMISTRY From the periodic table, we see that the atomic number (number of protons) for the element carbon is 6. The name carbon-14 tells us that this isotope’s mass number is 14. The chemical symbol for carbon is C. Now write the isotopic notation for carbon-14: 14 6𝐶 We can determine the number of neutrons as 14-6 = 8 neutrons 48 Given the isotopic notation 22𝑇𝑖 , identify the following: a. Name of the isotope a. Titanium-48 b. Mass number b. 48 c. Atomic number c. 22 d. Number of protons d. 22 e. Number of neutrons e. 48 – 22 = 26 ENCHEM30 NUCLEAR EQUATIONS In a chemical reaction, we write the symbols for various chemical elements but in NUCLEAR CHEMISTRY a nuclear reaction, we must also explicitly indicate protons, neutrons, and electrons that are produced during the course of nuclear fission or fusion reaction. While writing the nuclear equation, we have to mention the numbers of protons and neutrons present in all the elements. ENCHEM30 NUCLEAR EQUATIONS The following points need to be considered while writing nuclear equations. ✓ A nuclear equation must be balanced. NUCLEAR CHEMISTRY ✓ The symbol for an atom or atomic particle should include the symbol of the element, the atomic number and mass number. ✓ The mass number of atom (which is used to describe the number of protons and neutrons) should be attached at the upper left of the symbol. ✓ The atomic number of atom (which is used to describe the number of protons in the nucleus) should be attached at the lower left of the symbol. ENCHEM30 Examples of Balanced Nuclear Equations NUCLEAR CHEMISTRY NOTE! The nuclear equation must be balanced with respect to nuclear charge (atomic number) and nucleus mass (mass number). ENCHEM30 NUCLEAR STABILITY Nuclear Stability is a concept that helps to identify the stability of an isotope. The two main factors that determine nuclear stability are the neutron/proton ratio and the total number of nucleons in the nucleus. NUCLEAR CHEMISTRY Nuclear stability refers to the tendency of a nucleus of an atom to decay, which means to change into something else. Isotopes of atoms with unstable nuclei are called radioisotopes. ENCHEM30 NUCLEAR STABILITY Isotope Stability The graph of stable elements is commonly referred to as the Band (or NUCLEAR CHEMISTRY Belt) of Stability. The graph consists of a y-axis labeled neutrons, an x-axis labeled protons, and nuclei. At the higher end (upper right) of the band of stability lies the radionuclides that decay via alpha decay; below is positron emission or electron capture, above is beta emissions, and elements beyond the atomic number of 83 are only unstable radioactive elements. Stable nuclei with atomic numbers up to about 20 have an neutron:proton ratio of about 1:1 (solid line). ENCHEM30 NUCLEAR STABILITY An isotope is an element that has same atomic number but different atomic mass compared to the periodic table. Every element has a proton, neutron, and electron. NUCLEAR CHEMISTRY The number of protons is equal to the atomic number, and the number of electrons is equal to the protons, unless it is an ion. To determine the number of neutrons in an element, you subtract the atomic number from the atomic mass of the element. Atomic mass is represented as (A) and atomic number is represented as (Z) and neutrons are represented as (N). A= N+ Z ENCHEM30 NUCLEAR STABILITY The principal factor for determining whether a nucleus is stable is the neutron-to-proton ratio. Elements with (Z