GC 1 Evolution of the Atomic Theory Module PDF

BASIC EDUCATION SENIOR HIGH SCHOOL DEPARTMENT UPHSDCC-QAD-LH04242024...

BASIC EDUCATION SENIOR HIGH SCHOOL DEPARTMENT UPHSDCC-QAD-LH04242024 First Quarter General Chemistry 1 AY 2024-2025 Evolution of the Atomic Theory LESSON OBJECTIVES At the end of the lesson, the students will be able to: ▪ Define and characterize an atom ▪ Enumerate the 5 Postulates of Dalton’s Atomic Theory ▪ Count the number of subatomic particles in an atom ▪ Define and characterize isotopes ▪ Performance Task: Create Atomic models using Phet Simulation ATOM -From the Greek Word “Atomos” means Indestructible/ indivisible -Smallest particle of an element which is indivisible Introduction Atomic theory first originated with Greek philosophers around 2500 years ago. This basic theory remained unchanged until the 19th century when it first became possible to test the theory with more sophisticated experiments. As science has rapidly advanced over the past few centuries the atomic theory has been refined in accordance with the accepted scientific principles and theories of the time. Ancient Atomic Theory Leucippus The atomic theory of matter was first proposed by Leucippus, a Greek philosopher who lived at around 400BC.At this time the Greeks were trying to understand the way matter is made. According to Leucippus, eventually you arrive at small particles which cannot be further subdivided. Leucippus called these indivisible particles atoms (from the Greek word atomos, meaning “indivisible”). Democritus Leucippus's atomic theory was further developed by his disciple,Democritus who concluded that infinite divisibility of a substance belongs only in the imaginary world of mathematics. Democritus suggested the atomic theory, explaining that all things are"composed of minute, invisible, indestructible particles of pure matter which move about eternally in infinite empty." If a sample of a pure element was divided into smaller and smaller parts, eventually a point would be reached at which no further cutting would be possible—this was the atom of that element. According to the ancient Greeks, atoms were all made of the same basic material, but atoms of different elements had different sizes and shapes. The sizes, shapes, and arrangements of a material’s atoms determined the material’s properties. ARISTOTLE -“Everything is made of Four ELEMENTS: water, air, fire, and earth.” Plato and Aristotle attacked Democritus’s atomic theory on philosophical grounds rather than on scientific ones. Aristotle argued that it was unclear and certainly unwarranted to assume that atoms have or lack particular properties. Aristotle disagreed with Democritus and offered his own idea of the composition of matter. According to Aristotle, everything was composed of four elements: earth, air, fire, and water. Democritus' theory better explained things, but Aristotle was more influential, so his ideas prevailed. It took almost two thousand years before scientists came around to seeing the atom as Democritus did. Brgy. Paciano Rizal, Calamba City, Laguna, 4027 Philippines  Tel. No.: (049) 834-1159 www.perpetualdalta.edu.ph Calamba Campus  BASIC EDUCATION SENIOR HIGH SCHOOL DEPARTMENT UPHSDCC-QAD-LH04242024 The Modern Atomic Theory John Dalton -BILLIARD BALL MODEL or SOLID SPHERE MODEL For centuries scientists did not have the methods or technology to test their theories about the basic structure of matter, so people accepted the ancient Greek view. In the 19th century John Dalton made inferences that exhibited how atoms bond together in definite proportions. Dalton was able to say that atoms of different elements combine in whole number ratios. This theory, to go along with four other theories, made up what Dalton called the "Modern Atomic Theory. “Included in these were two theories that stated atoms could not be divided or destroyed, a theory that stated different elements contain different chemical properties, and atoms of the same element contain the same chemical properties. The Modern Atomic Theory Dalton’s Atomic Theory 1.Elements are composed of small particles called atoms 2.Atoms of an element are identical, having the same properties such as mass, size and chemical properties 3.Compounds are composed of 2 different elements and the ratio of each element is an integer or a simple fraction. 4.A chemical reaction results to rearrangement of atoms giving new combinations to atoms. 5. Atoms can neither be destroyed nor created in chemical reactions The law of conservation of mass(Antoine Lavoisier) The law of conservation of mass states that in ordinary chemical and physical changes, mass is notcreated or destroyed. It is only transformed into different substances. The law of definite composition(Joseph Proust) The law of definite composition states that “all samples of a given compound have the same proportions of their constituent proportions.” Expanding the Modern Atomic Theory J.J. Thomson - credited for discovering the electron. -Plum Pudding Model or Chocolate Chip cookie model CATHODE RAY TUBE EXPERIMENT He created a tube that had a positively charged anode on one side and a negatively charged cathode on the other side.He then applied a magnet to the middle of the tube and discovered that negatively charged particles were emanating towards the positive magnetic field. From this, he concluded that negatively charged particles, called electrons, were present in atoms. Thomson then created the Plum Pudding model, which suggested that electrons and protons were randomly placed throughout the atom. ROBERT MILLIKAN -computed the mass of electrons -OIL DROP EXPERIMENT -He computed the mass of the electron to be 9.1094 x 10-28 g using the oil drop experiment. Millikan oil-drop experiment, first direct and compelling measurement of the electric charge of a single electron. -A closed chamber with transparent sides is fitted with two parallel metal plates, which acquire a positive or negative charge when an electric current is applied. At the start of the experiment, an atomizer sprays a fine mist of oil droplets into the upper portion of the chamber. Under the influence of gravity and air resistance, some of the oil droplets fall through a small hole cut in the top metal plate. When the space between the metal plates is ionized by radiation (e.g., X-rays), electrons from the air attach themselves to the falling oil droplets, causing them to acquire a negative charge. A light source, set at right angles to a Brgy. Paciano Rizal, Calamba City, Laguna, 4027 Philippines  Tel. No.: (049) 834-1159 www.perpetualdalta.edu.ph Calamba Campus  BASIC EDUCATION SENIOR HIGH SCHOOL DEPARTMENT UPHSDCC-QAD-LH04242024 viewing microscope, illuminates the oil droplets and makes them appear as bright stars while they fall. The mass of a single charged droplet can be calculated by observing how fast it falls. By adjusting the potential difference, or voltage, between the metal plates, the speed of the droplet’s motion can be increased or decreased; when the amount of upward electric force equals the known downward gravitational force, the charged droplet remains stationary. The amount of voltage needed to suspend a droplet is used along with its mass to determine the overall electric charge on the droplet. Through repeated application of this method, the values of the electric charge on individual oil drops are always whole-number multiples of a lowest value—that value being the elementary electric charge itself (about 1.602 × 10−19 coulomb). Ernest Rutherford -Nuclear Model of atom -Discovered Proton and Nucleus Gold Foil Experiment In 1911 British scientist Ernest Rutherford set out to test Thomson’s proposal by firing a beam of charged particles at atoms. Alpha particles are heavy particles with twice the positive charge of a proton. Alpha particles are now known to be the nuclei of helium atoms, which contain two protons and two neutrons. Ernest Rutherford's experiment was to emit alpha particles towards a thin gold sheet. Rutherford would then determine where the deflections of the alpha particles would go, and therefore be able to theorize what kind of placement protons and electrons had. -Together with Hans Geiger and Ernst Marsden, Rutherford deduced the structure of the atom. -Rutherford observed that most of the alpha particles went straight through the foil. However a large proportion were deflected through small angles an some (though very few) deflected straight back. Rutherford then theorized that there was something called a nucleus, which contained a high density of positively charged particles. Rutherford was able to say there was a nucleus because alpha particles that deflected right back must have hit something more massive and with a strong positive charge. This led Rutherford to propose a very different model for the atom. -Instead of supposing that the positive charge and mass were spread throughout the volume of the atom, he theorized that it was concentrated in the center of the atom. Rutherford called this concentrated region of electric charge the nucleus of the atom. Niels Bohr -Planetary Model -Bohr's greatest contribution to modern physics was the atomic model. The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. -Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element. -The chemical element bohrium (Bh), No. 107 on the periodic table of elements, is named for him. Erwin Schrodinger Quantum Mechanical Atomic Model -used the wave-particle duality of the electron to develop and solve a complex mathematical equation that accurately described the behavior of the electron in a hydrogen atom. The quantum mechanical model of the atom comes from the solution to Schrödinger's equation. - Erwin Schrödinger formulated a wave equation that accurately calculated the energy levels of electrons in atoms. -Solutions to the Schrödinger wave equation, called wave functions, give only the probability of finding an electron at a given point around the nucleus. Electrons do not travel around the nucleus in simple circular orbits. The location of the electrons in the quantum mechanical model of the atom is often referred to as an electron cloud. JAMES CHADWICK -discovered Neutron BERYLLIUM BOMBARDMENT EXPERIMENTS Brgy. Paciano Rizal, Calamba City, Laguna, 4027 Philippines  Tel. No.: (049) 834-1159 www.perpetualdalta.edu.ph Calamba Campus  BASIC EDUCATION SENIOR HIGH SCHOOL DEPARTMENT UPHSDCC-QAD-LH04242024 -He performed the beryllium bombardment experiments himself and interpreted that radiation as being composed of particles of mass approximately equal to that of the proton but without electrical charge— neutrons. -He performed the beryllium bombardment experiments himself and interpreted that radiation as being composed of particles of mass approximately equal to that of the proton but without electrical charge—neutrons. That discovery provided a new tool for inducing atomic disintegration, since neutrons, being electrically uncharged, could penetrate undeflected into the atomic nucleus and led to a new model of the atomic nucleus being composed of protons and neutrons. Brgy. Paciano Rizal, Calamba City, Laguna, 4027 Philippines  Tel. No.: (049) 834-1159 www.perpetualdalta.edu.ph Calamba Campus