Comprehensive History of the Development of Atomic Theory PDF

Comprehensive History of the Development of Atomic Theory Lesson Objectives By the end of the lesson, students will be able to… ⮚ trace the development of atomic theory from the philosophical concept of indivisible particles in ancient Greek to the contemporary quantum mechanical model...

Comprehensive History of the Development of Atomic Theory Lesson Objectives By the end of the lesson, students will be able to… ⮚ trace the development of atomic theory from the philosophical concept of indivisible particles in ancient Greek to the contemporary quantum mechanical model; and ⮚ identify and summarize the  Atomic Models ⮚ This model of the atom may look familiar to you. This is the Bohr model. ⮚ In this model, the nucleus is orbited by electrons, which are in different energy levels. ▪ A model uses familiar ideas to explain unfamiliar facts observed in nature. ▪ A model can be Introduction ⮚ Atomic theory is the scientific theory that matter is composed of fundamental building blocks known as atoms. ⮚ This idea dates back thousands of years and has evolved significantly. ⮚ It's a journey from the philosophical speculations of ancient times to the high-energy particle experiments of today's large hadron colliders.  Ancient Philosophies and Early The Greek Philosophers ⮚ The notion of atoms was first proposed in the 5th century BCE by Greek philosophers Leucippus and his student Democritus. ⮚ They suggested that everything in the universe is composed of small, indestructible units called atoms (from the Greek 'atomos', meaning indivisible). ⮚ However, these ideas were purely speculative, as they had no experimental evidence to support them. Explain, in your own words, what Democritus believed about the nature of matter.  Why is Democritus's contribution to atomic theory considered fundamental even though he did not have experimental evidence?  Democritus (circa 400 B.C.) Who was Democritus? ⮚ Democritus speculated that matter could not be divided indefinitely, leading to the concept of atoms, meaning 'indivisible' ⮚ Believed atoms were eternal, infinite in number and kind, moving through the void, differing in shape, and size but Who was Democritus? ⮚ To Democritus, atoms were small, hard particles that were all made of the same material but were different shapes and sizes. ⮚ Atoms were infinite in number, always moving and capable of joining This theory was ignored and forgotten for more than 2000 years! The eminent philosophers of the time, Aristotle and Plato, had a Aristotle and Plato favored more respected, the earth, fire, air and water approach to the nature of (and ultimately matter. Their ideas held sway because of their eminence as philosophers. The atomos wrong) theory. idea was buried for Roman Influence Later, the Roman poet Lucretius expanded on Greek atomism in his work "De Rerum Natura" ("On the Nature of Things"), which offered a detailed description of the physical universe where atoms were the core building blocks. Alchemy and Early Chemistry The Alchemists During the Middle Ages and into the Renaissance, alchemists attempted to transform substances into other forms (e.g., lead into gold) and in doing so, they experimented with materials in ways that set the stage for a more scientific understanding of matter. The Renaissance to Early Modern Period The Sceptics Many Renaissance scholars were skeptical of atomic theory because it contradicted the then-dominant Aristotelian doctrine, which posited that matter was continuous and could be divided infinitely. The Renaissance to Early Modern Period The Chemists In the 17th century, the first meaningful progress toward modern atomic theory arose with individuals like Robert Boyle, who argued against the Aristotelian view of the four elements and proposed that matter was composed of various combinations of different substances. John Dalton ⮚ John Dalton was an English (1803) chemist and physicist, acclaimed for developing the modern atomic theory and studying color blindness, a condition sometimes called Daltonism in his honor. ⮚ His work on atomic weights and chemical reactions significantly advanced the field of chemistry. John Dalton (1803) Revitalized and expanded the atomic theory for the scientific community of his time Stated that atoms of different elements are characterized by differences in weight Formulated the law of multiple proportions, explaining how atoms combine in simple whole numbers to form compounds John Dalton (1803) ⮚ He deduced that all elements are composed of atoms. Atoms are indivisible and indestructible particles. ⮚ Atoms of the same element are exactly alike. ⮚ Atoms of different elements are different. ⮚ Compounds are formed by the joining of atoms of two or more elements. Note: This theory became one of the foundations of modern chemistry. John Dalton (1803) Note: This theory became one of the foundations of modern chemistry.  Describe Dalton's atomic theory and how it differed from Democritus's ideas.  Discovery of Subatomic Particles Discoveries in Electricity ⮚ The late 19th century saw a wave of discoveries related to electricity, which eventually led to the understanding that atoms themselves were not indivisible. ⮚ Experiments by scientists like Michael Faraday laid the groundwork for this revelation. The Periodic Table ⮚ Dmitri Mendeleev’s periodic table in 1869 organized elements by atomic weight, noticing that certain properties repeated periodically, which provided further insight into the structure and behavior of atoms. Discovery of Subatomic Particles J.J. Thomson (1897) ⮚ J.J. Thomson was a British physicist who won the Nobel Prize in Physics in 1906 for discovering the electron, a subatomic particle, and for his work on the conduction of electricity in gases. ⮚ His experiments with cathode rays led to a new understanding of atomic structure, fundamentally altering the field of physics. J.J. Thomson (1897) ⮚ Through experiments with cathode rays, he discovered the electron, suggesting that atoms are divisible ⮚ Thomson studied the passage of an electric current through a gas. ⮚ As the current passed through the gas, it gave off rays of negatively charged particles. J.J. Thomson (1897) ⮚ This surprised Thomson, because the atoms of the gas were uncharged. Where had the negative charges come from? ⮚ Thomson concluded that the negative charges came from within the atom. ⮚ A particle smaller than an atom had to exist. ⮚ The atom was divisible! J.J. Thomson (1897) ⮚ Thomson called the negatively charged “corpuscles,” today known as electrons. ⮚ Since the gas was known to be neutral, having no charge, he reasoned that there must be positively charged particles in the atom. ⮚ But he could never find J.J. Thomson (1897) ⮚ Conceived the 'Plum Pudding' model where negative electrons reside in a positive matrix  What was the significance of J.J. Thomson's discovery of the electron?  Why was the "Plum Pudding" model eventually discarded? Radioactivity In 1896, Henri Becquerel discovered radioactivity, and subsequently, Ernest Rutherford and others identified three types of emissions from radioactive materials: alpha, beta, and gamma rays. Alpha Particles Alpha particles were recognized as a type of radioactive emission that could be deflected by magnetic and electric fields, indicating they had a charge. Ernest Rutherford (1911) ⮚ Ernest Rutherford was a New Zealand-born British physicist renowned for his pioneering studies of radioactivity and the atomic nucleus. ⮚ He is credited with the discovery of the proton and the formulation of the nuclear model of the atom, often referred to as the Rutherford model. ⮚ His work earned him the Nobel Prize in Chemistry in 1908. Ernest Rutherford (1911) ⮚ Rutherford’s experiment Involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick) Ernest Rutherford (1911) ⮚ Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all. ⮚ Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges. Ernest Rutherford (1911) ⮚ This could only mean that the gold atoms in the sheet were mostly open space. Atoms were not a pudding filled with a positively charged material. ⮚ Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.” ⮚ He called the center of the atom the “nucleus” ⮚ The nucleus is tiny compared to the atom as a whole. Ernest Rutherford (1911) ⮚ Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. ⮚ The negatively charged particles were scattered outside the How did Rutherford's model change the way scientists view the atom?  Quantum Mechanics and the Modern Atomic Model  Niels Bohr (1922) ⮚ Niels Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922. ⮚ He is known for the Bohr model of the atom, which introduced the theory of electrons orbiting the nucleus in distinct energy levels.  Niels Bohr (1922) ⮚ According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. ⮚ These orbits, or energy levels, are located at certain distances from Niels Bohr (1922)  What are the key features of Bohr's model of the atom? Arnold Sommerfeld ⮚ Arnold Sommerfeld was a German theoretical physicist who made significant contributions to atomic and quantum theory. ⮚ He is known for refining the Bohr model with his introduction of elliptical orbits and for developing the Sommerfeld fine- structure constant, which quantifies the strength of the electromagnetic interaction between elementary charged particles. Arnold Sommerfeld  In what way did Sommerfeld refine the Bohr model?  Erwin Schrödinger ⮚ (1926) Erwin Schrödinger was an Austrian- Irish physicist and one of the founders of quantum mechanics. ⮚ He is best known for his development of the Schrödinger equation, a fundamental result in the field, for which he shared the Nobel Prize in Physics in 1933. ⮚ He is also famous for the thought experiment "Schrödinger's cat," which illustrates the concept of superposition in quantum theory.  Erwin Schrödinger ⮚ Formulated the (1926) wave equation that bears his name, foundational to quantum mechanics ⮚ Described electrons in terms of probability clouds or orbitals, rather than fixed orbits What was revolutionary about Schrödinger's wave equation? Werner Heisenberg (1927) ⮚ Introduced the Uncertainty Principle, positing fundamental limits to the precision with which certain pairs of physical properties, like position and momentum, can be known ⮚ His principle has profound implications for the philosophy of science and the objective reality of quantum mechanics What does the Uncertainty Principle state, and what are its implications for the behavior of subatomic particles?  James Chadwick ⮚ James Chadwick was(1932) a British physicist who was awarded the Nobel Prize in Physics in 1935 for the discovery of the neutron, a neutral particle in the atomic nucleus that plays a fundamental role in the structure and stability of atoms. ⮚ Led to a more accurate understanding of atomic structure and isotopes. How did the discovery of the neutron contribute to the atomic model?