Q1_Lesson 1_Formation of Elements.pdf
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PHYSICAL SCIENCE Quarter 1 Lesson 1: Formation of Light and Heavy Elements Elements are essential in the formation of matter. It ori...
PHYSICAL SCIENCE Quarter 1 Lesson 1: Formation of Light and Heavy Elements Elements are essential in the formation of matter. It originated from the expansion of the universe 14 billion years ago which is called as the ‘Big bang’. During this event, light elements were formed such as hydrogen and helium, together with small amounts of lithium and beryllium through a series of nuclear fusion (combination process) reactions that constitutes the fundamental energy source of stars, like the Sun. On the other hand, heavier elements were from the moment when the cloud of dust and gases from the Big bang cooled down that led to the formation of stars and galaxies. The Big Bang Theory and the Formation of Light Elements Based from the big bang theory, the universe went through a huge expansion 14 billion years ago. Back then, the universe is made of hot and dense particles with high energies. As the universe expands, everything also cooled down, giving a way to the formation of protons and neutrons. Types of Nuclear Reactions The formation of light elements during the big bang started from a more complex process when nuclei are produced which is called Big Bang Nucleosynthesis. Nuclear reactions are processes in which a nucleus either combines with another nucleus (through nuclear fusion) or splits into smaller nuclei (through nuclear fission). The following are the most common types of nuclear reactions, together with illustrative examples. Alpha decay (𝜶-decay) is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or ‘decays’ into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two. Example: Alpha decay of polonium-210 Beta decay (𝜷-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar (each of two or more isotopes of different elements, with the same atomic weight). Example: Beta decay of carbon-14 Gamma radiation is a type of radioactivity in which some unstable atomic nuclei dissipate excess energy by a spontaneous electromagnetic process. This often happens after alpha or beta decay has occurred. Since only energy is emitted during gamma decay, the number of protons remains the same. Example: Gamma radiation in alpha decay of uranium-238 Positron emission or beta plus decay (𝜷+decay) is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron (𝑒+10) and an electron neutrino (νe). Example: Positron emission of oxygen-15 Electron capture is a process that unstable atoms can use to become more stable. During electron capture, an electron (𝑒−10) in an atom's inner shell is drawn into the nucleus where it combines with a proton, forming a neutron and a neutrino. The neutrino is ejected from the atom's nucleus. Example: Electron capture of mercury-201 Bombardment reactions involve the nucleus of the atom being bombarded (hence the name) with particles from the nucleus or an entire nucleus. Examples of the particles are neutrons and alpha particles. These reactions usually give off a different particle than the one that they were bombarded with. Example: Bombardment of beryllium with an alpha particle Big bang nucleosynthesis (BBN), or also known as the primordial nucleosynthesis, is a process where light elements were produced during the expansion of the universe. An American cosmologist Ralph Alpher was able to prove the process of BBN through his calculations on the proportions of protons and neutrons present in the early universe. Also, with his right knowledge of these proportions, he was able to predict that elements such as hydrogen and helium can be formed. During the first three minutes of the rapid expansion of the universe, rapid cooling also occurs, thus slowing down the sub-atomic particles, which provides more opportunities for binding together to form light elements. Below are the detailed explanations of the formation of light elements. 1. Deuterium (D), an isotope of hydrogen, as first formed from the fusion of a proton and a neutron, accompanied by the emission of high-energy photon (𝛾 ). 2. Tritium (T), or hydrogen-3, was produced from the fusion of two deuterium nuclei and a release of a proton. PHYSICAL SCIENCE Quarter 1 3. Helium-3, an isotope of helium with one neutron and two protons, was formed from the fusion of two deuterium nuclei and a release of a neutron. 4. Helium-4 can be synthesized from deuterium and helium-3. Also, He-4 can be formed when a deuterium fuses with a tritium atom. 5. Lithium-7, an unstable nucleus with three protons and four neutrons, was produced from the nuclear fusion of helium-4 and tritium. Lithium-7 decayed naturally to form two stable helium nuclei. 6. Beryllium-7 was produced from helium-3 and helium-4. Beryllium-7 also reacts with a neutron and decays to the unstable lithium-7, with the subsequent release of a proton. Isotopes. These are chemical elements that has the same number of protons but different number of neutrons (that is, a greater or lesser atomic mass) than the standard for that element. For example: Carbon 12, Carbon-13, and Carbon-14 are isotopes PHYSICAL SCIENCE Quarter 1 Stellar Evolution and the Formation of Heavy Elements Stars, which are giant balls mostly made of hydrogen and helium, act as sites for nuclear reactions in the universe. Through the process, they are able to fuse light elements to form heavier elements. These reactions also involve light emission, which is the reason why stars are so bright. Stages of Stellar Evolution Outlined below are the many steps involved in a star’s evolution, from its formation in a nebula, to its death as a white dwarf or neutron star. Nebula. It is a cloud of gas (hydrogen) and dust in space. Nebulae are the birthplaces of stars. Star. It is a luminous globe of gas producing its own heat and light by nuclear reactions (nuclear fusion). Red giant. It is a large bright star with a cool surface. It is formed during the later stages of the evolution of an intermediate-mass star like the Sun, as it runs out of hydrogen fuel at its center. Red dwarf. These are very cool, faint and small stars, approximately one tenth the mass and diameter of the Sun. White dwarf. It is very small, hot star, the last stage in the life cycle of a star like the Sun. Supernova. It is the explosive death of a star, and often results in the star obtaining the brightness of 100 million suns for a short time. Neutron stars. These stars are composed mainly of neutrons and are produced when a supernova explodes, forcing the protons and electrons to combine to produce a neutron star. Neutron stars are very dense. Black holes. These are believed to form from massive stars at the end of their lifetimes. The gravitational pull in a black hole is so great that nothing can escape from it, not even light. As the universe continue to expand for several years, the cloud of hydrogen and helium gases condensed to form stars. Over millions of years, the stars made of hydrogen became hotter and denser. Moreover, during the process of stellar evolution, nuclear reactions continued producing elements heavier than lithium. To form heavy elements such as carbon, neon, oxygen, silicon, and iron, the light elements combined through the process of stellar nucleosynthesis. Formation of Heavy Elements As hydrogen and helium were scattered in the universe during its expansion, these two elements gave a way for the formation of heavy elements. Hydrogen initially fueled young stars and through nuclear reactions, new elements are formed in certain regions or layers of a star called the fusion shells. When most of the hydrogen in the core is fused into helium, fusion stops and the pressure in the core decreases. Gravity squeezes the star to a point that helium-hydrogen burning occur. Thus, converting helium into carbon. When the majority of the helium in the core has been converted to carbon, the rate of alpha fusion processes decreases. Gravity again squeezes the star. The star goes through a series of stages where heavier elements are fused in the core and in the shells around the core. The element neon is formed from carbon fusion; oxygen from neon fusion; silicon from oxygen fusion; and iron from silicon fusion. The star then becomes a multiple-shell red giant. The figure below shows an illustration of a multiple-shell red giant. Figure 1. Multiple-Shell Red Giant Supernova Nucleosynthesis During the stellar nucleosynthesis, burning of fusion shells can only from heavy elements up to iron. If stellar nucleosynthesis produced elements only up to iron, then how do elements heavier than iron are formed? Synthesis of heavier nuclei happened via neutron or proton capture processes. Neutron capture can be slow or rapid. Slow neutron capture or s-process happens when there is a small number of neutron. It is termed slow because the rate of the neutron capture is slow compared to the PHYSICAL SCIENCE Quarter 1 rate of beta decay. Therefore, if a beta decay occurs, it almost always occurs before another neutron is captured. Rapid neutron capture or r-process happens when there is a large number of neutrons. It is termed rapid because the rate of neutron capture is fast that an unstable nucleus may still be combined with another neutron just before it undergoes beta decay. The r-process is associated with a supernova. The temperature of a supernova is tremendously high that the neutrons are moving very fast. Because of their speed, they can immediately combine with the already heavy isotopes. This type of nucleosynthesis is also called as the supernova nucleosynthesis. Proton capture or p-process is the addition of a proton in a nucleus. It happens after a supernova, when there is a tremendous amount of energy available. It is because the addition of a proton to the nucleus is not favorable because of Coulombic repulsion, which is the repulsive force between particles with the same charge. Proton capture produces a heavier nucleus that is different from the seed nucleus. SUMMARY 1. The big bang theory is a cosmological model that describes how the universe started its expansion about 13.8 billion years ago. 2. Big bang nucleosynthesis (BBN), also known as primordial nucleosynthesis, is the process of producing light elements during the big bang expansion. 3. Nuclear reactions are involved in the formation of light and heavy elements. 4. The correlation between the predicted and observed cosmic abundances of hydrogen and helium was the major proof of the big bang theory. 5. Stellar nucleosynthesis is the process by which elements are formed within stars. 6. The primary factor that determines how stars evolve is mass. 7. The star formation theory proposes that stars form due to the collapse of the dense regions of a molecular cloud. 8. Stellar evolution is the process by which a star changes during its lifetime. 9. Heavy elements such as carbon, oxygen, silicon, neon, and oxygen are formed in stellar evolution. 10. Elements heavier than iron are formed through supernova nucleosynthesis by the process of neutron and proton captures. Atomic Number and the Synthesis of New Elements We all know that matter can exist in the form of elements, compounds, and mixtures. When elements were discovered, a proper classification was required for their easier and better understanding. Many scientists adopted several ways to classify elements. They tried to find out some patterns or regularity in the properties of elements. The Atomic Number and the Synthesis of New Elements In 1808, John Dalton came up with the theory that marked the beginning of the modern era of chemistry. His postulates may be summed up to what is known as Dalton’s atomic theory. Johann Wolfgang Döbereiner (1780-1849) In 1829, the German chemist Johann Wolfgang Döbereiner published a report of his previous observations that there were groups of three elements, hence Döbereiner’s triads, which had similar physical properties. According to him, when these triads were arranged in order of their increasing atomic masses, he observed that the mass number of the middle element was approximately the mean of the atomic masses of the first and the third elements. Döbereiner found 4 triads (12 elements) that fit to his observation. However, the rest of the known elements when grouped into triads did not follow the concept of Döbereiner’s traids. John Newlands (1837-1898) After the failure of Döbereiner’s traids, the next attempt to classify elements was done by a British chemist, John Newlands. By this time, 56 elements were discovered. He arranged these elements in an increasing order of atomic masses and found that every eighth had properties similar to that of the first. He compared this to the octaves found in music and therefore, this classification was known as Newlands Octaves. However, this classification had its own share of shortcomings, the main points being that Newlands could arrange elements only up to Calcium out of 56 known elements. After which, the elements did not show similar properties. Also, several new elements, which did not feature in Newlands classification were discovered. PHYSICAL SCIENCE Quarter 1 Dimitri Ivanovich Mendeleev (1834-1907) After the failure of Newlands Octaves, Dimitri Ivanovich Mendeleev, a Russian chemist, put forward a periodic table that was called Mendeleev Periodic Table. He examined the relationship among atomic masses of elements, and their physical and chemical properties. He believed that the atomic mass of the element was the most fundamental property in classifying the element. He arranged the known elements according to their increasing atomic masses and their properties. Thus, creating the first periodic table with 63 elements. In the Mendeleev’s periodic table, the horizontal rows are called periods. There is a total of seven periods in his periodic table numbered using Hindu Arabic numerals. The vertical columns in the periodic table are called groups. There is a total of eight groups in Mendeleev’s periodic table numbered using Roman numerals. Mendeleev kept blank spaces in this periodic table. The vacant spaces were for elements that are yet to be discovered. In addition, when noble gases were discovered, they were place in Mendeleev’s periodic table without disturbing the position of other elements. However, the Mendeleev’s periodic table has its own demerits. Firstly, there was no fixed position could be given to hydrogen in the table as it resembled alkali metals as well as halogens. Secondly, at certain places, an element of higher atomic mass has been placed before an element with lower mass. For instance, cobalt (Co = 58.93) is placed before nickel (Ni = 58.71). Also, some elements placed in the same sub-group had different properties. For example, Manganese (Mn) is placed with halogens which totally differ in properties. Due to these irregularities, a new classification emerged. Henry Gwyn Jeffreys Moseley (1887-1915) In 1913, an English physicist named Henry Moseley discovered that atomic number is the most fundamental property of an element and not its atomic mass. This discovery changed the whole perspective of elements and their properties. Accordingly, Mendeleev’s periodic law was modified into Modern periodic law. The current periodic table was based on the modern periodic law called the modern periodic table. Furthermore, Mendeleev was still considered as the father of periodic table because he had his work published first. SUMMARY: 1. In arranging elements in the periodic table, Johann Wolfgang Döbereiner made his first attempt through his triads. Döbereiner’s triads suggests that elements are arranged in order of their increasing atomic PHYSICAL SCIENCE Quarter 1 masses, when he observed that the mass number of the middle element was approximately the mean of the atomic masses of the first and the third elements. 2. John Newlands made the second attempt of arranging the elements in the periodic table. He arranged 56 elements in an increasing order of atomic masses and found that every eighth had properties similar to that of the first. He compared this to the octaves found in music and therefore, this classification was known as Newlands Octaves. 3. Dimitri Ivanovich Mendeleev was known as the Father of Periodic Table. He proposed the Mendeleev’s Periodic Law which states that “The physical and chemical properties of elements are a periodic function of their atomic masses.” 4. On the other hand, Henry Gwyn Jeffreys Moseley arranged the elements in the periodic table with their increasing atomic number. He modified Mendeleev’s Periodic Law into Modern Periodic Law which states that “The physical and chemical properties of elements are a periodic function of their atomic numbers.” 5. Moreoever, four elements were synthesized through nuclear transmutation and radioactive studies. These are elements 43, 61, 85, and 87 or otherwise known as Technetium, Promethium, Astatine, and Francium. REFERENCES: Cruzpero, R. (2019, May 15). UP TALKS | Nucleosynthesis: Formation of the Elements [Video]. Retrieved from https://www.youtube.com/watch?v=TgBo-bCVijQ Esguerra, J. H., Dapul, G. R., Salazar, M., & Bantang, J. Y. (2016). Teaching Guide for Senior High School Physical Science. Quezon City: Commission on Higher Education. HistoryPod. (2016, March 5). 6th March 1869: Dmitri Mendeleev presents the first periodic table [Video]. Retrieved from https://www.youtube.com/watch?v=31tF4nbQRHg Newlands Laws of Octaves. (2020, June 13). Retrieved from https://www.examfear.com/notes- dir/00/00/11/00001143.html Pogge, R. W. (2006, January 21). Astronomy 162: Introduction to Stars, Galaxies, & the Universe. Retrieved from http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit2/himass.html Santiago, K. S., & Silverio, A. A. (2016). Exploring Life Through Science Series - Senior High School Physical Science. Quezon City: Phoenix Publishing House, Inc.
