The Atom, Its Structure, and Its Development PDF

SH1690 The Atom, Its Structure, and Its Development Atoms from the Eyes of Philosophers and Scientists The Four Classical According to the fundamental Greek theory of matter, as proposed by the Elements natural philosopher Empedocles (...

SH1690 The Atom, Its Structure, and Its Development Atoms from the Eyes of Philosophers and Scientists The Four Classical According to the fundamental Greek theory of matter, as proposed by the Elements natural philosopher Empedocles (490-430 BC), everything came from the four (4) classical elements -- Fire, Air, Water, and Earth (that which became the basis of every action fantasy genre in fiction). He even asserted that each element is associated with two (2) distinct properties, which, given the proper proportions required to "mix" these elements, create everything. For example, the metal iron is classified as earth and air material because it exists as a cold and dry object but becomes hot and moist when melted. Living creatures (yes, including humans) have the softness and life that only water and fire can provide. You can refer to these properties below. Figure 1. The classical elements and their properties as proposed by Empedocles, named as pyr (fire), aer (air), ydor (water), and ge (earth) The Four Classical Aristotle (384-322 BC) supported Empedocles' idea about the four elements Elements: Now with and even added a fifth one: Aether (sometimes spelled ether or æther). This Aether! idea then prevailed during his time, up until the end of the 17th century! This principle is also used by alchemists in their studies. 03 Handout 3 *Property of STI Page 1 of 8  SH1690 Figure 2. The classical elements of pyr, aer, ydor, and ge was also accompanied by aither (aether) Atomism: The Democritus (460-370 BC) was one (1) of the many Greek philosophers who Movement that was didn't agree with the "Five Elements" theory. He believed that everything is Left Ignored made of very small particles, which can be achieved through numerous divisions of material until the tiniest material couldn't be divided any further. This particle, dubbed atomos (Gk. "undivided"), was stated to be the origin of all things. However, this idea didn't sit well with Aristotle. Because of Aristotle's popularity and assertion over the Five Elements theory (and that all matter is continuous and can be divided infinitely), the Atomism movement was largely ignored, until the 1800s. Alchemy: The Alchemists intertwined their chemical endeavors with spiritual and mystical Precursor to concepts, including the study of the five (fire, air, water, earth, and aether) Chemistry classical Western elements, to transmute base metals such as iron and tin into "pure" metals such as gold and platinum. They also used these to discover universal cures for all diseases and achieve longevity (or immortality). Though these proto-chemists all failed in their quests, their studies paved the way for the discovery of common compounds we now use today, such as soaps, charcoal, and color dyes. Alchemy also contributed to the rise of using systematic, logical approaches to the study, expanded knowledge for medicinal chemistry, and even helped develop industrial chemistry. 03 Handout 3 *Property of STI Page 2 of 8  SH1690 The Birth of The Five Elements theory held its ground for years, until Robert Brown Chemistry published his research in 1661, entitled The Sceptical Chymist (The Skeptical Chemist). This encouraged scientists to conduct experiments and use the results to further develop chemistry. In 1808, John Dalton came up with a theory that marked the beginning of the modern era of chemistry. His postulates, dubbed as Dalton's atomic theory, is summarized as follows: 1. Elements are made up of small indivisible particles called atoms; 2. In any given pure element, all properties of a particular element are uniform throughout its atoms. Atoms of different elements differ in their properties; 3. Compounds are composed of atoms of different elements. The component atoms in a given compound exist only in whole-number ratios (i.e., no fraction or decimal values); 4. Atoms are conserved in chemical reactions -- they are only rearranged, separated, or combined with other atoms. Dalton's concepts about matter and atoms were more detailed than the Atomism movement proposed by Democritus. Though he didn't study the atom itself, he surmised these during his research on water, where the atoms of a certain gas (named hydrogen) combined with another gas (i.e., oxygen) to form water. He stated that both elements have different properties despite both existing in the gaseous states. His [Dalton] third postulate is named the Law of Multiple Proportions, where it illustrates that if two (2) or more different compounds are composed of the same two (2) elements, then the ratio of the masses of the second element combined with the given mass of the first element is always a ratio of small whole numbers (you can refer here for more information). This law supported Joseph Proust's findings of the composition of matter. In 1779, Proust proposed an important principle that quantitatively analyzed chemical reactions. He [Proust] suggested that the formation of compounds involves the combination of elements in similar proportions by mass regardless of the sample size. Dalton's last postulate is now known as the Law of Conservation of Mass because matter is neither created nor destroyed. Since there are other discoveries in between these major game changers in Chemistry, here is the summary of those events. A Timeline on the Brief History on Matter and Atoms Year Significant Event 450 BC Empedocles asserted that all things are composed of four (4) primal elements. 400 BC Democritus formed the Atomism movement. Aristotle supported Empedocles' theory and proposed that matter is continuous and can 380-320 BC be divided infinitely. 1799 Joseph Proust proposed the Law of Definite Proportions. 1808 John Dalton formulated the Atomic theory and proposed the Law of Multiple Proportions. 03 Handout 3 *Property of STI Page 3 of 8  SH1690 Dmitri Mendeleev (can also be Mendeleyev or Mendeleef) rearranged all known chemical 1869 elements in his time in a table based on their atomic masses, essentially creating the very first Periodic Table. Antoine Becquerel and Marie Curie observed that radioactivity causes some atoms to The 1890s break down spontaneously. 1895 Wilhelm Röntgen (or Roentgen) discovered X-rays. 1897 Joseph John "J.J." Thomson discovered electrons. Thomson also proposed the "plum-pudding" atom model, where electrons are dispersed 1904 throughout the atom itself. 1908-1917 Robert Millikan found that an electron has a charge of −1.6022 × 10−19 C (coulombs). 1910-1911 Ernest Rutherford noted that atoms are mostly space. Niels Bohr proposed the "orbital" or "planetary" atom model. 1913 Henry Gwyn Jeffreys Moseley (or Henry Moseley) used x-ray spectra to study atomic structures. 1919 Rutherford discovered protons. 1932 James Chadwick discovered neutrons. The Structure of an Atom An atom is defined as the smallest unit of a chemical element, containing all the properties of that element. It has two (2) basic parts: the nucleus and the electrons. Electrons are tiny particles that move around the nucleus, carrying a negative nuclear charge equal to −1.6022 × 10−19 coulombs. The nucleus is the central part of the atom that carries its atomic mass. It is made of two (2) nucleons: protons and neutrons. Protons are tiny particles 1,836 times heavier than electrons and carry nuclear positive charges equal (yet, opposing) to the charge value of electrons. Neutrons are tiny particles that are slightly heavier than protons and carry zero (0) nuclear charge. Atomic Number and Atomic Mass The discovery of the subatomic particles prompted other scientists to study the variations in the characteristics of elements! English physicist Henry Gwyn Jeffreys Moseley experimentally found that different metals bombarded with electrons emitted x-rays of varying degrees. He attributed these differences to the metals' differing positive charges contained in their nuclei. By correlating the resulting frequencies to certain whole number values, each element gets its atomic number. The atomic number is the number of protons in a chemical element, serving as its identity as written in the Periodic Table. The number of protons and electrons in an atom dictates its charge. Ideally, an element is neutral if both protons and electrons have the same number. If neutrons are added with protons, which are neutrally charged, they form the atom's atomic mass! The atomic mass (sometimes referred to as the mass number) is the number of protons and neutrons combined. It dictates how heavy an atom's nucleus (and the atom itself) is. Normally, all chemical elements 03 Handout 3 *Property of STI Page 4 of 8  SH1690 have neutrons. Hydrogen is the only element without any neutrons. That doesn't mean that it will never have one, though! We can summarize this by referring to the reference image below. Figure 3. How to read a chemical element's symbol and its coefficients Both atomic mass and atomic number are used in arranging elements and identify their properties. Dmitri Mendeleev created the very first Periodic Table, arranging the elements according to their atomic masses. There were some gaps in it, hinting that there were (and still are) elements yet undiscovered. However, Henry Moseley argued that the elements must be arranged through their atomic numbers. This configuration is still being used in modern-day Periodic Tables. Isotopes and Nuclear Decay In most cases, atoms of a certain chemical element have different masses. Previously, we have established that all atoms in a given element have the same properties, including its atomic mass and number! Both statements can't be true, is it? Well, in the study of both Chemistry and Physics, it can be possible through isotopes. Isotope is a term used by chemists and physicists to call a variation of an element. Each isotope has the same atomic number, but they differ in atomic mass. Figure 4. The various isotopes of hydrogens Source: http://terpconnect.umd.edu/~wbreslyn/chemistry/isotopes/isotopes-of-hydrogen.html As an example, hydrogen has three (3) isotopes. Its base isotope is protium, while both deuterium and tritium are its variant isotopes. These isotopes are the ones first made after the events of the Big Bang. But, not all isotopes are named the same way hydrogen's isotopes do. Instead, isotopes of other elements are named in two (2) ways. First, they can be named the same way presented in the previous image. As an example, given are three (3) known isotopes of the chemical element Carbon, its base isotope being the first in the series. 03 Handout 3 *Property of STI Page 5 of 8  SH1690 Figure 5. The various ways the isotopes of carbon existing on Earth The second method of naming isotopes is by writing its name (or elemental symbol) followed by a dash and its associated atomic mass. Using the previous example, we can rewrite them as: 1. Using the elemental symbol a. C-12 b. C-13 c. C-14 2. Using the chemical name a. Carbon-12 b. Carbon-13 c. Carbon-14 Not all isotopes are stable, however. If an element has an unstable isotope, it undergoes a process known as radioactive decay. The process of radioactive decay (also known as nuclear decay) stabilizes an unstable isotope by releasing its excess mass in the form of radiation. Radioactive decay has three (3) types: alpha (α), beta (β), and gamma (γ) decay. Alpha-decay is the process where an unstable chemical element releases a helium nucleus, also known as an Alpha-particle (α), from its unstable nucleus to achieve stability. Doing this converts the unstable chemical element into another element, although its stability may vary. When observed in a cloud chamber, the ejected particle travels in a straight line because of its mass. As an example, the given equation is the alpha decay of Polonium-210. Mathematically, it is written as, , where, X Original Element A Original atomic mass Z Original atomic number Y New element after decay Subsequently, if an α-particle is launched directly to an element, it creates a new one and ejecting a neutron in the process. Mathematically,. As an example, given is the α-bombardment of beryllium-9. 03 Handout 3 *Property of STI Page 6 of 8  SH1690 The method of nuclei bombardment is not limited to helium nuclei. Scientists have also used isolated element nuclei and bombard them to other elements to create new elements. Take the element Darmstadtium (Ds). This heavy metallic element is made by bombarding Pb-208 atoms with isolated nuclei of Ni-62. This gave them,. Beta-decay is the process where an unstable chemical element releases a beta-particle (β) to achieve stability. Doing this does NOT convert the unstable chemical element into another element. The unstable element tries to stabilize itself by converting a neutron inside it into a proton, releasing the excess mass as a β-particle. When observed in a cloud chamber, β-decay particles travel in curved paths. This process is done in three (3) ways. The first version of β-decay is called a "β-Minus" decay because it ejects an electron after achieving stability through β-decay. As an example, given is the β-minus decay of carbon-14. Mathematically,. The second version of β-decay is called a "β-Plus" decay. This one ejects a positron after achieving stability through β-decay. A positron is the antiparticle counterpart to an electron. Antiparticles are the primary study in the field of antimatter. As an example, given is the β-plus decay of oxygen-15. Mathematically,. The third version of β-decay does NOT involve any ejection of particles. This one has the atom absorbing its electron to create a neutron for stability. This form of β-decay is known as the "Electron Capture." This decay is supported by the given notion that an electron's negative charge, combined with a proton's positive charge, creates a neutron, with its excess momentum and energy ejected as an electron neutrino (see the given equation). 𝑝 + 𝑒 → 𝑛 + 𝜈𝑒. As an example, given is the decay of mercury-201. Gamma decay is the process that is always active and in conjunction with the other decay processes. It releases a gamma (γ) particle, a massless particle that has both momentum and energy. The energy γ- particle carries the excess energy resulting from the decay of a radioactive element. Mathematically, 𝑎𝑛𝑦 𝑑𝑒𝑐𝑎𝑦 𝑝𝑟𝑜𝑐𝑒𝑠𝑠 → 𝑟𝑒𝑠𝑢𝑙𝑡𝑖𝑛𝑔 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 + 00𝛾. Using the previous examples, we can rewrite them to have γ-emissions. 03 Handout 3 *Property of STI Page 7 of 8  SH1690 Gamma decay is also known to spontaneously occur onto itself without undergoing any other decay methods. This is done to release more excess energy because of its instability. This is mostly observed in highly radioactive materials such as uranium-238, although it can be done by other materials. As an example, uranium-238 is highly radioactive. Thus, it constantly releases mass and energy to stabilize itself. Reference: Santiago, K.S., & Silverio, A. A. (2016). Exploring life through science: Physical science (1st ed). Phoenix Publishing House. 03 Handout 3 *Property of STI Page 8 of 8