UGEB2380 The Chemistry of Life Lecture Notes 2024-25 PDF

UGEB2380 The Chemistry of Life Academic Year 2024-25 Dr. Sam CK HAU (Department of Chemistry) Nuclear Chemistry and Energy from Electron Transfer Nuclear Power Much of the electricity we have come to depend on, day after day, comes from nuclear power Throughout the US, 100 nuclear rea...

UGEB2380 The Chemistry of Life Academic Year 2024-25 Dr. Sam CK HAU (Department of Chemistry) Nuclear Chemistry and Energy from Electron Transfer Nuclear Power Much of the electricity we have come to depend on, day after day, comes from nuclear power Throughout the US, 100 nuclear reactors, located in 30 states, provide about 20% of the electricity used there 3 Radioactivity First discovered by Antoine Henri Becquerel in 1896, that the element uranium emitted X-rays His graduate student Marie Curie took up the investigation and named such phenomenon as Radioactivity i.e. the emission of radiation by the spontaneous decay of an unstable atomic nucleus 4 Radioactivity Two conditions underlying radioactivity Radioactive nuclei contain 84 or more protons The ratio of neutrons to protons within a radioactive nucleus is either above or below a stable range C14: 8n & 6p (radioactive) C13: 7n & 6p (stable) C12: 6n & 6p (stable) C11: 5n & 6p (radioactive) 5 Types of Radioactive Decay Ernest Rutherford identified two kinds of decay: 𝛼 (alpha) radiation and 𝛽 (beta) radiation Paul Villard discovered the third kind 𝛾 (gamma) radiation 6 Alpha Radiation The radiation results from the discharge of 𝛼-particles, which are clusters of two protons and two neutrons Equivalent to the nuclei of He-4 atoms Always results in the conversion of the radiative element into a new element Mass Number Mass Number total 241 241 95Am 237 93Np + 4 2 𝛼 Atomic Number Atomic Number total 95 Photo Credit: International Atomic Energy Agency (IAEA) 7 Beta Radiation The radiation results from spontaneous discharge of 𝛽-particles, which are fast-moving electrons, travelling at 90% of the speed of light Mass number does not change but the atomic number increase by 1, and generate a new element The beta particle is represented as -10β. The –1 of the -10β indicates the single negative charge beta emission + Neutron Proton Electron Neutral Particle (+) (–) beta decay 137 137 0 55Cs 56Ba + –1β Photo Credit: International Atomic Energy Agency (IAEA) 8 Gamma Radiation A form of electromagnetic radiation Ca wave) Greater energy than X-ray, able to penetrate deeply into matter and can cause considerable biological harm Emitted during the relaxation of nuclei from excited and high energy state Denoted as 00𝛾 or simply 𝛾 ; no mass and no electrical charges Photo Credit: International Atomic Energy Agency (IAEA) 9 Ionising Radiation & neutral ionize When 𝛼, 𝛽 and 𝛾 rays penetrating matters, they can generate ions by expelling the outer-shell or valence electrons from the atoms and molecules they strike - Ionising Radiations When hitting living tissues, the ions generated will convert into free radicals - highly reactive molecules containing unpaired electrons and potentially causing damages to cells and tissue Photo Credits: https://terryshp.com 10 Penetrating Power The ability of ionising radiation to penetrating matters Alpha particles - easily be stopped by paper or a few centimetres of air Beta particles - be stopped by a thick sheet of aluminium foil, a block of dense wood or heavy clothing Gamma rays - pass through most substances with ease and require a thick shield of lead or concrete to block Penetrating power ⬇ ; Ionising power ⬆ easier find i to sih to / ionize Radioactive Decay Radon: a colourless and odourless noble gas - Rn-222 - a radioactive isotope undergoes alpha-decay to Polonium (Po-218) from rocks and soils During our respiration, Rn-222 may residue inside our lungs and generate minuscule amounts of polonium and other radioactive isotopes ➠ could do considerable biological damage like lung cancer - A good example of At background radiation (very low levels of radiation from the natural sources) 12 Background Radiations Rem: a unit of ionising radiation representing an equivalent dose to humans, regardless of the types of radiation Rough estimate: a resident of the US receives an average of about 600 mrem (600 x 10-3 rem) per year, half of which comes naturally from background radiations Cosmic radiation: high energy radiation continuously enter the earth from the outer space -Banana emit 𝛽 and small amount of 𝛾 radiations Potassium-40 within our foods and bodies soils emit 𝛼, 𝛽, and 𝛾 rays Radioactive isotopes like Ra, U, Po … in 13 Acute Exposure to Radiation Large dose of ionising radiation ( > 50 rem) have the capacity to - transform enzymes, cell membranes, DNA into new, useless or harmful molecular forms Such damage is extensive enough to cause illness or death - somatic damage (軀體損傷) like reducing amount of white blood cells, fatigue, nausea, damage to organs, glands, bone marrows, lead to leukaemia and other cancers, even genetic damage Alexander Litvinenko, a former Russian intelligence officer was poisoned with the radioisotope polonium-210 in 2006, dying just three weeks later. 14 Half-life Knowing what type of radiation, or the identity of I isotopes are important But it is important to know the RATE of the decay as well Half-life - the length of time it takes for one half of a given quantity of a radioactive isotope to decay Every radioisotope has its own characteristic half-life E.g. Polonium-210 has a half- life of 138 days; 5.0 g of Po-210, after 138 days, 2.5 g remains; another 138 day, only 1.25 g left and so on… 15 Radiocarbon Dating Carbon-14, with characteristic half-life of 5730 years Useful for determining the age of residues of living or once-living things Establish the ages of ancient / objects of plant or animal HHF 7) origin Useful tool in Archeology and Art History B six] Enee , Other Applications X-ray - bone only Most valuable use in medical applications, like imaging, diagnostic procedure and medical therapies The radioisotope widely be used is technetium-99m (99mTc), m refers to metastable or excited state It decays with the loss of 𝛾 ray alone 0𝛾 sithemity rays EE] 99m 99 0 43Tc 43Tc + organs, emit 𝛾 rays and exit Be introduced in various the body; half-life is just 6 I hrs (Radiotracers) - -12)  Other Applications Positron Emission ↳ ]IF Step 1: Positron Emission Tomography (PET) 11 11 0 Positron - a electron analog 6C 5B + 1e carries a positive charge Step 2: Positron/Electron Annihilation 2 00 𝛾 ~***g layers Like Carbon-11, be introduced produce a cascade of 𝛾 rays 0 0 into a bodily organ and –1 e + 1e Detector will convert the signals into powerful diagnostic images representing slices or planes of > - the organ EY-St organ Fluorine-18 incorporated with a glucose - help analysis the f path of glucose within the brain and to diagnose or treat brain abnormalities #hydroxide group > - F (label glucose) Finge Cell ↓ Other Applications Gamma Knife Radiosurgery Cancer cells divide more rapidly and more metabolic active than normal cells More susceptible to be radiation such as 𝛾 rays from damaged by ionising Each of 𝛾 ray with low cobalt-60 intensity but from different angles Individually, too weak to kill the surrounding healthy tissue; the rays will be converged to focus to the tumor and destroy its growth Unleashing the Power of Nucleus ip Nuclear Fission - a reaction that splits a relatively massive nucleus into two or more sizeable fragments, releasing energy in the process Otto Hahn and Lise Meitner discovered nuclear fission in 1944 A Uranium-235 nucleus absorbs one neutron, then split into two fragments (Kr-92 and Ba-141) and release three neutrons Photo Credits: https://chem.libretexts.org Nuclear Fission The fission of U-235 releases several neutrons Anyone of these would penetrate into another U-235 nucleus and continue the chain of energy-releasing process A cascading chain reaction begins 21 Isotope Enrichment FEE Investigation found that addition of a neutron toO U-235 is more effective than that to U-238 However, > 99% naturally occurring Uranium is U-238 and less than 1% is U-235, which is a big challenge A process of increasing the abundance of a desired isotope in a mixture by removing the undesired isotope 22 Gaseous Centrifugation Molecules of 238UF6 have a slightly higher mass than 235UF6 Heavier 238UF6 tend to migrate gradually to the walls of the spinning chamber, while the gas at the centre enriches slowly with 235UF6 Repeat the process in successive stages Fuel for nuclear power ~ 3% U-235; but for nuclear weapon ~ 90% U-235 T T 23 Nuclear Power Cheat) Fission chain reaction releases energy instantaneously With good design, the energy release can be made to a slow, controlled process The energy release can convert water into steam, which turns blades of turbine to generate electricity - Pressurised Water Reactors (PWR) radiation ↑ 24 Nuclear Power Cheap, plentiful and pollution free power Can reduce carbon emissions significantly 190 %) st Offset the need for coal-fired France Now : power plants Makes a far smaller demand - 2nd Now on land area than other renewable energy facilities (like wind or solar) of equivalent capacity X renewable 25 Nuclear Power Nuclear Waste Letit Consists of a large number ↳ A region) of radioactive isotopes by- products, along with residual nuclear fuel, which is below useful levels but still hazardous Some can remain dangerous for a long time owing to their long half-life Usually be vitrified (fused with molten glass, then packed into corrosive- resistant container, stored deep underground in a geographically stable national waste repository) 26 Nuclear Power Questions of safety Accident list 1. Three mile island, Pennsylvania (1979) 2. Chernobyl, Ukraine (1986) 3. Fukushima, Japan (2011) Long lead time to build new plants (take > 20 yrs) Nuclear proliferation - potentially make weapon- grade material 27 Nuclear Fusion A nuclear reaction in which light nuclei fuse together with the release of energy The reverse of nuclear fission The fusion of hydrogen atoms to form a helium atom results in a fractional loss of mass and released as energy Produce the energy of sun; however, no materials or designs are available for the extraordinary high temperature - Nuclear equation: 12H (D) + 13H (T) 4He 2 + 01n 28