Chapter 1: Elements in the Universe PDF

Name :....................................................... Class :........... Chapter 1: Elements in the Universe Summary "We are all made out of stardust". The Big Bang is the origin of all matter in the universe. The study of...

Name :....................................................... Class :........... Chapter 1: Elements in the Universe Summary "We are all made out of stardust". The Big Bang is the origin of all matter in the universe. The study of chemistry and astrophysics enables us to correlate how elements are formed and how they evolved. ***This summary is exactly what it is, a summary. Details of the main points you should know, for the rst part of the chapter, can be found in the mind maps each group prepared*** 1 Element Factories All the elements today can trace their origins either to the Big Bang directly or to various cosmic processes occurring in stars and during the explosive events that mark the end of stellar lifecycles (stellar and supernova nucleosynthesis, neutron star mergers). 1.1 Elements Formed from the Big Bang The main process here involves the fusion of protons on neutrons during the extremely high temperatures in the rst moments of the universe. The lightest elements were formed directly after the Big Bang : hydrogen and helium (along with their isotopes). 1.2 Stellar Nucleosynthesis Occurs mainly in stars. Lighter elements fuse together via nuclear reactions to form heavier elements. Two well-known processes are the proton-proton chain reaction and the triple-alpha process. In the former, hydrogen nuclei fuse to forme helium, in the latter, helium nuclei fuse to form elements like carbon and oxygen. Elements with atomic numbers up to 26 (iron, Fe) are formed using this process. For heavier elements, the process is endothermic, requiring more energy than it releases. 1ere EURO Chapter 1 1 1.3 Supernova Nucleosynthesis There are dierent types of supernovae that contribute to how heavier elements are formed. A Type II supernova (core-collapse) occurs when a massive star's core collapses under gravity after exhausting its nuclear fuel. The resulting shockwave ejects outer layers and facilitates rapid neutron capture (r-process), forming elements heavier than iron (like gold, platinum). A Type Ia supernova occurs in binary systems where a white dwarf accretes mass from a com- panion star, reaches a critical mass (also known as the Chandrasekhar limit), and undergoes a thermonuclear explosion. This process primarily produces iron, nickel, and other elements up to iron. 1ere EURO Chapter 1 2 1.4 Neutron Star Mergers When two neutron stars in a binary system fall into a common orbit, then gradually spiral inward due to their gravity systems. When they collide, they create a kilonova, releasing vast amounts of energy and neutrons. The r-process during these mergers is responsible for the creation of elements heavier than iron.. Gravitational waves from neutron star mergers (which is usually accompanied by a short gamma-ray burst) have been detected by interferometers. 1.5 Cosmic Distribution The spread of elements in the universe is due to explosive events (like supernovae) and stellar winds (process of stars losing mass). These processes scatter matter into the vast space between clusters of galaxies, also referred to as the interstellar medium. Gas and dust enriched with elements from previous generations are reused to make new stars and systems, also known as the cosmic recycling process. 1ere EURO Chapter 1 3 2 Elements Essential for Life Certain elements are esential for life to develop. These include, but are not limited to, carbon, nitrogen, oxygen, phosphorus, sulfur. All organic molecules contain a carbon chain, due to its ability to form strong covalent bonds. These molecules include : proteins, nucleic acids (that make up RNA and DNA), carbohydrates, lipids. The main processes include : photosynthesis, respiration, decomposition, and transformations due to fossil fuels, as shown in the diagram below : Nitrogen is a key element of amino acids (which are used to build proteins), nucleic acids, and ATP (energy molecules). The nitrogen cycle includes processes such as nitrication (where it is converted into nitrites or nitrates), assimilation (where plants absorb nitrates and convert them into organic mole- cules), ammonication (where decomposers convert organic nitrogen back into ammonia), and denitrication (where bacteria release nitrogen back into the atmosphere). 1ere EURO Chapter 1 4  Oxygen is an element vital for aerobic respiration (particularly of living beings), a process that releases energy by breaking down glucose. Phosphorus is essentiel for DNA, RNA, and cell membranes (cycling through rocks, water, and living organisms). Sulfur is found in certain amino acids and vitamins, and is important for protein synthesis and metabolic processes. 3 Identiying Elements Scientists identify elements in stars and other celestial bodies through their interaction with electromagnetic radiation. Spectroscopy is a key tool in this analysis, and understanding the types of spectra and their origins is crucial for this. 1ere EURO Chapter 1 5 3.1 Continuous Spectra A continuous spectrum appears as a smooth and uninterrupted distribution of light across all visible wavelengths, ranging from violet (short wavelengths) to red (long wavelengths). This type of spectrum is emitted by hot, dense objects, such as stars or solid, liquid, or very dense gases. This results from the movement of charged particles. As these particles vibrate and accelerate, they emit electromagnetic radiation. Because these objects radiate across the full range of wavelengths, they create a spectrum with no distinct lines. Examples : The Sun's photosphere, incandescent light bulbs, or any object at a high tempe- rature that radiates due to its thermal energy. 3.2 Emission Spectra An emission spectrum is produced by hot, low-density gases. Unlike a continuous spectrum, an emission spectrum consists of bright, discrete lines, each corresponding to a specic wavelength of light. Atoms in the gas are excited by energy (from heat, light, or collisions), causing electrons to move to higher energy levels. As the electrons return to their lower, more stable energy states, they release photons at specic wavelengths, producing bright lines. Each element has its own unique pattern of lines, known as its spectral ngerprint. This means that scientists can determine which elements are present in space and their relative abundances. Examples : Nebulae, auroras, and gas discharge tubes (e.g., neon signs) 3.3 Absorption Spectra An absorption spectrum appears as a continuous spectrum interrupted by dark lines at specic wavelengths. 1ere EURO Chapter 1 6  As light passes through a cooler gas, photons with energies matching the energy dierence between electron energy levels in the atoms of the gas are absorbed. The gas then re-emits this energy, but in random directions, resulting in dark lines where light is absorbed from the original source. Absorption spectra allow scientists to determine the chemical composition of stars, planets, and other celestial bodies. By examining which wavelengths are missing from the continuous spectrum, astronomers can infer the presence of specic elements in the outer layers of stars or in interstellar gas clouds. Examples : The absorption spectra of stars (such as the Sun) and planets. Another example of an emission spectrum is the dark lines in the spectrum of sunlight, known as Fraunhofer lines. The letters at the top of the Fraunhofer spectrum correspond to specic absorption lines, each associated with dierent elements present in the Sun's atmosphere. Here's what each of the most common labels generally represents : A : Oxygen (O2 ) - Absorption by oxygen molecules in Earth's atmosphere, not the Sun. B : Oxygen (O2 ) - Another oxygen line due to Earth's atmosphere. C : Hydrogen (H) - Part of the Balmer series. D : Sodium (Na) - Known as the sodium doublet, prominent in the yellow part of the spectrum. E : Iron (Fe) - Iron absorption lines in the green part of the spectrum. F : Hydrogen (H) - Another Balmer series line in the blue part of the spectrum. G : Iron (Fe) and Calcium (Ca) - Lines in the violet part of the spectrum. H and K : Calcium (Ca) - Strong absorption lines in the violet, often seen in spectra of stars. 3.4 Hertzprung-Russell Diagram The Hertzsprung-Russell (HR) diagram is a fundamental tool in astrophysics for studying the properties and life stages of stars. It is a graph that plots stars according to their brightness (magnitude) and temperature (color). The X-axis is typically represented by the colour index (e.g., g-r) or temperature. Hotter, blue stars have lower values and are placed on the left, while cooler, red stars have higher values and are on the right. The Y-axis shows the star's magnitude (brightness). Brighter stars (lower magnitude values) are plotted at the top, while fainter stars (higher magnitudes) are at the bottom. 1ere EURO Chapter 1 7  The H-R diagram has several regions : ◦ Main Sequence : A diagonal band from the top-left (hot, bright stars) to the bottom-right (cool, dim stars). Most stars, including the Sun, spend the majority of their life in this region, where they are fusing hydrogen into helium in their cores. ◦ Giants : Located above the main sequence, these are large, bright stars with cooler tem- peratures (often red or orange). Once solar mass stars have moved all their hydrogen into helium, they evolve into red giant. At this point, the hydrogen shell surrounding the core of the star begins to burn, producing even more Helium. ◦ Supergiants : When the hydrogen shell burning is nished, the shell of helium begins fusing into heavier elements such as carbon and oxygen. As this happens, the star moves into the supergiants region. ◦ White Dwarfs : Found in the lower-left corner, these are hot but faint stars that represent the nal life stage for many low- and medium-mass stars. Once all the helium has been fused into other elements, the outer layers of the star are ejected outwards into planetary nebula. The exposed core of the star, which is made up of carbon and oxygen, is a white dwarf. A white dwarf gradually becomes fainter and cooler as it cannot sustain the fusion process. This process happens fairly quickly compared to the main sequence. 1ere EURO Chapter 1 8  Activity 1 : Nuclear Marshmallows Objective : Investigate nuclear reactions and how basic building blocks of matter are "broken down". Material : Marshmallows (big and small) Some information : Nuclear reactions dier from basic chemical reactions in that they involve the separation of particles inside the nuclei of atoms. Within the nucleus the protons and neutrons are bound together by very strong forces, so a large amount of energy is required to overcome these forces to separate a nucleus into its component protons and neutrons. Likewise, if the same nucleus were formed from the individual protons and neutron , this ame large amount of energy would be released and the nucleus wold be more table than the protons and neutrons from which it was formed. The binding energy of a nucleus is the energy needed to break it into its individual protons and neutrons. In nuclear ssion, a heavy nucleus splits into lighter nuclei and energy is released. In nuclear fusion, light nuclei combine to produce a stable, heavier nucleus, and particles and energy are released. When writing equations for nuclear reactions, the formalism used to denote elements shows the Z X , where A represents the chemical symbol of the element, number of protons and nucleons : A Z the number of protons, and A the number of nucleons (protons + neutrons). In nuclear processes, some of the particles that can be emitted or absorbed are shown in the table below : In this activity, you will model the nuclei of dierent elements using marshmallows, and visualise how dierent nuclear reactions take place. A neutron is represented by one big and one small marshmallow stuck together with a toothpick, a proton is represented by one big marshmallow, and an electron is represented by one small marshmallow. 1ere EURO Chapter 1 Instructions : 1. Build the nucleus of a neutral carbon atom 12 6 C. 2. Perform your measurements by recording the time for 10 full swings (back and forth) and calculate the average period. Repeat for each pendulum length and record your data. 3. Calculate the mean period √ for each pendulum length and graph the period (T) against the square root of the length ( L). Does your graph show a linear relationship ? 4. Why is it necessary to repeat measurements in scientic experiments ? Discuss how human error and other variables can aect the results. 5. What do you observe about the period when the pendulum is released at larger angles (e.g., 30° vs. 10°) ? Does the formula for the period of a pendulum hold true for large angles ? 6. What is the dierence between accuracy and precision ? How can you determine if a mea- surement is accurate or precise ? How could friction and air resistance aect the results, and how might you minimise these eects ? 1ere EURO Chapter 1