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Atoms & Their Structure. Chapter 2 Section 1 Part 1. Objectives. How have historic experiments led to the development of the modern model of the atom? How is the modern model of the atom different from previous models?
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Atoms & Their Structure Chapter 2 Section 1 Part 1
Objectives • How have historic experiments led to the development of the modern model of the atom? • How is the modern model of the atom different from previous models? • What information is available in an element block of the periodic table?
Important Vocabulary • Atom • Atomic theory • Law of conservation of mass/matter • Law of definite proportions • Electron • Proton • Electron cloud • Isotope • Neutron • Nucleus • Atomic number • Mass number • Atomic mass unit • Atomic mass
The Atom • An atom is the smallest particle of an element that retains its identity in a chemical change • The concept of the atom intrigued a number of early scientists and philosophers • However, they could not observe individual atoms
History of Atoms • The idea of the atom first came from a Greek philosopher Democritus nearly 2500 years ago • It started with a set of simple questions, “If you take a piece of chalk and break it in half, are both halves still chalk? If you continue to divide each piece, is there a limit to the division before it becomes something else?” • Democritus thought there was a limit which he called atomos, meaning “unable to be cut” • This idea that matter is made of the fundamental particles called atoms is known as the atomic theory of matter
Democritus' Theory of Atoms • All matter consists of invisible particles called atoms. • Atoms are indestructible. • Atoms are solid but invisible. • Atoms are homogenous. • Atoms differ in size, shape, mass, position, and arrangement. • He believed that the movements of atoms caused the changes in matter he observed • However, he had no way of proving the existence of atoms
Contributors to Atomic Theory • Democritus • Antoine Lavoisier • Joseph Proust • John Dalton • J.J Thomson • Hantaro Nagaoka • Ernest Rutherford • Niels Bohr • Erwin Schrodinger • Werner Heisenberg • Robert Millikan • Eugene Goldstein • James Chadwick • Irene Joliot-Curie
Antoine Lavoisier • In 1782, the French taxman Lavoisier made measurements of chemical reactions in sealed containers • He observed that the mass of reactants before the reaction was equal to the mass of the products after the reaction • He concluded that when an chemical reaction occurs, matter is neither created nor destroyed but only changed • This idea became known as the Law of Conservation of Mass/Matter
Joseph Proust • In 1799, a French chemist Joseph Proust observed that the compostion of water is always 11.2% hydrogen and 88.8% oxygen by mass • He studied many other compounds and observed that compounds were always in certain proportions by mass • This principle is referred to as the Law of Definite Proportions
John Dalton • Was a teacher, chemist, meteorologist, & physicist • He is best known for his development of the modern atomic theory • He also did research into color blindness (sometimes called Daltonism)
Dalton’s Atomic Theory • Was established in the early 1800’s before the Periodic Table • Dalton believed that a few kinds of atoms made up all matter • He also believed that elements were composed of only one kind of atom and compounds were made from two or more kinds of atoms • He reasoned that only whole numbers of atoms could combine to form compounds
Five Principles of Dalton’s Theory • All matter is composed of atoms which cannot be subdivided, created, or destroyed • Atoms of a given element are identical in their physical and chemical properties • Atoms of different elements differ in their physical and chemical properties • Atoms of different elements combine in simple, whole-number ratios to form compounds • In chemical reactions, atoms are combined, separated, or rearranged
The Problem with Dalton’s Theory • It explained most of the chemical data that existed during his time • However, it doesn’t all hold true today • Atoms can be divided into particles • Atoms can be created and destroyed • It doesn’t account for molecules & allotropes • Thus, it changed