physical science ppt_module6.powerpoint presentation

Physical Science 12 module 6 PowerPoint presentation

1. PHYSICAL SCIENCE MODULE 6

2. HOW THE ELEMENTS FOUND IN THE UNIVERSE WERE FORMED

3. Big Bang Theory proposed that due to the expansion of universe, hydrogen and helium were produced. As the years go by, these light elements (hydrogen and helium) condensed and formed stars , including the sun. Over millions of years, the stars made of hydrogen became hotter and denser. With these occurrence, stellar nucleosynthesis started. This Photo by Unknown Author is licensed under CC BY STELLAR NUCLEOSYNTHESIS Is the process by which elements are formed within stars by nuclear reactions. The abundances of these elements change as the stars evolve. STELLAR FORMATION AND EVOLUTION

4. EVOLUTION OF STARS The theory suggest that stars form due to the collapse of the dense regions of an atomic cloud is known as the star formation theory . As the cloud collapses, the fragments contract to form a stellar core called protostar. The protostar contracts and its temperature increase due to strong gravitational force. Nuclear reactions release positrons, and neutrinos which increase pressure and stop the contraction. When the contraction stops, the gravitational equilibrium is reached, and the protostar becomes a main sequence star .

5. ydrogen is fused into helium in the core of a main sequence star through the proton-proton chain. When most of the hydrogen in the core is fused in the helium the fusion stops, and the pressure in the core decreases. Gravity squeezes the star to a point that hydrogen and helium burning occur. Helium converts to carbon in the core while hydrogen is changed to helium in the shell surrounding the core. The star becomes a red giant. HYDROGEN AND HELIUM FUSION H

6. n a low-mass star, carbon fusion is not possible due to insufficient mass. As helium in the core converts to carbon, the fusion rate slows down, causing the star to contract. This contraction eventually leads to the expulsion of the outer material, leaving behind a hot, inert carbon core. This core will eventually cool down and become a white dwarf. Unlike low-mass stars, massive stars have the necessary mass to achieve the temperature and pressure required for carbon fusion. Through a series of stages, these stars fuse heavier elements, starting with oxygen and progressing to neon, magnesium, silicon, and finally iron. This process occurs in the core and surrounding shells of the star. I

7. he star's core fuse, iron is eventually produced. While elements lighter than iron release energy during fusion, fusing two iron nuclei requires energy input. Therefore, massive stars can only produce elements up to iron. When the core can no longer produce enough pressure to resist gravity, it collapses, leading to a supernova explosion. This explosion releases a large amount of energy and produces elements heavier than iron. T

8. Pieces of Evidence The discovery of interstellar gas and dust has been crucial in supporting the theory of star formation. By studying various stages of star formation occurring in different regions of space, astronomers can piece together a clear understanding of how stars are formed. Infrared Radiation (IR) During star formation, energy is released in the form of infrared radiation (IR). Astronomers measure the IR emitted by a protostar and compare it to the IR from a nearby area where no absorption occurs (zero extinction). The difference in IR due to gas and dust helps in approximating the energy, temperature, and pressure in the protostar. The Nuclear Fusion Reactions in Stars Stellar nucleosynthesis, the process by which elements are created within stars, occurs through nuclear fusion. Lighter elements fuse to form heavier ones under high temperatures and pressures. This fusion process powers stars, allowing them to burn for extended periods. Hydrogen is the lightest element and the most abundant in the universe. Thus, the formation of heavier elements starts with hydrogen. Hydrogen burning is the stellar process that produces energy in the stars. There are two dominant hydrogen burning processes, the proton-proton chain and carbon-nitrogen-oxygen (CNO) cycle.

9. PROTON-PROTON CHAIN PROTON-PROTON CHAIN Is a series of thermonuclear reactions in the stars. It is the main source of energy radiated by the sun and other stars. It happens due to the large kinetic energies of the protons. If the kinetic energies of the protons are high enough to overcome their electrostatic repulsion, then the proton-proton chain proceeds. The sequence following proceeds The chain starts when two protons fuse and when the fuse breaks one proton is turned into a neutron. The proton and neutron then pairs, forming an isotope of hydrogen called deuterium. Another protons collides and with deuterium forming on helium-3 nucleus and a gamma ray. Finally, two helium-3 nuclei collide, and a helium-4 is created with the release of two protons

10. CARBON-NITROGEN-OXYGEN (CNO) CYCLE For more massive and hotter stars, the carbon-nitrogen- oxygen cycle is the more favorable route in converting hydrogen to helium. Unlike the proton-proton chain, the CNO cycle is a catalytic process. The cycle proceeds as follows: Carbon-12 captures a proton and gives off a gamma ray, producing an unstable nitrogen-13. Nitrogen-13 undergoes beta decay to form carbon-13. Carbon-13 captures a proton and release a gamma ray to become nitrogen-14. Nitrogen-14 then captures another proton and release a gamma ray to produce oxygen-15. Oxygen-15 undergoes beta decay and becomes a nitrogen-15. Finally, nitrogen-15 captures a proton and gives off helium (alpha particle) ending the cycle and returning to carbon-12.

11. Nucleosynthesis is the process by which new nuclei are formed from pre-existing or seed nuclei. There are different types of nucleosynthesis, such as: Big Bang nucleosynthesis, which produced hydrogen and helium. Stellar nucleosynthesis, which produced elements up to iron in the core of stars. For elements heavier than iron, nucleosynthesis requires different processes since fusion reactions become unfavorable after iron-56 due to decreasing **nuclear binding energy per nucleon. The synthesis of heavier elements happens through neutron capture or proton capture processes.

12. Synthesis of Heavier Nuclei - This happens via neutron or proton capture processes. Different pathways are needed for the synthesis of heavier nuclei due to changes in nuclear binding energy after iron-56. Neutron Capture - In this process, a neutron is added to a seed nucleus, producing a heavier isotope of the element. Slow Neutron Capture (s-process) - This occurs when there is a small number of neutrons available Rapid Neutron Capture (r-process) - This occurs when there is a large number of neutrons.

13. FORMATION OF HEAVIER ELEMENTS Henry Moseley, an English physicist, discovered that the properties of an element are determined by its atomic number, which is the number of protons in its nucleus. He conducted experiments by bombarding different elements with electrons and measuring the emitted X-rays. He found a mathematical relationship between the frequency of these X-rays and the element's position in the periodic table. This led to the rearrangement of the periodic table based on atomic numbers. However, there were four gaps in the table, which were later filled by artificially creating the missing elements through nuclear transmutations.

14. FORMATION OF HEAVIER ELEMENTS Discovery of Nuclear Transmutation Ernest Rutherford conducted an experiment in 1919 where he bombarded nitrogen nuclei with alpha particles from radium. This led to the transformation of nitrogen into oxygen, a process known as nuclear transmutation. While the alpha particles and atomic nuclei repel each other, neutrons are often used in particle accelerators to overcome this repulsion and synthesize new elements. The Discovery of the Missing Elements In 1925, there were four gaps in the periodic table. Using particle accelerators, two of these missing elements were synthesized in the laboratory. Particle accelerators utilize magnetic and electrical fields to accelerate protons, allowing them to overcome the repulsion between protons and target atomic nuclei and create new elements.

15. FORMATION OF HEAVIER ELEMENTS Ernest Lawrence played a crucial role in the discovery of missing elements. He used a linear accelerator to bombard molybdenum with neutrons, resulting in the creation of Technetium, the first artificially produced element.

16. FORMATION OF HEAVIER ELEMENTS The discovery of Astatine an element with atomic number 85. It was first produced in 1940 by Dale Corson, K. Mackenzie, and Emilio Segre . Astatine, element number 85, was first synthesized by bombarding bismuth with fast-moving alpha particles in a cyclotron. Due to its radioactive nature, the element was named after the Greek word " astatos ," meaning unstable. Discovery of Promethium and Francium Through studies in radioactivity, the remaining two missing elements, Promethium (element 61) and Francium (element 87), were discovered. Promethium was found in the waste products of uranium fission, while Francium was identified as a breakdown product of uranium.

17. FORMATION OF HEAVIER ELEMENTS Neptunium, the first transuranium element, was discovered in 1940 by Edwin McMillan and Philip Abelson. They bombarded uranium with neutrons in a particle accelerator and successfully produced neptunium, which has a half-life of 2.3 days. SYNTHESIS OF NEW ELEMENT

18. FORMATION OF HEAVIER ELEMENTS Dr. Glenn Seaborg , along with Edwin McMillan, Joseph Kennedy , and Arthur Wahl , later created Plutonium, another transuranium element, by bombarding uranium with deuterons in a cyclotron. All transuranium elements, including neptunium and plutonium, are artificially created and can only be produced in laboratories using nuclear reactors or particle accelerators. SYNTHESIS OF NEW ELEMENT

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