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The Atom Essay

1132 words - 5 pages

An Atom is the smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element. As such, the atom is the basic building block of chemistry.John Dalton -John Dalton developed the first useful atomic theory of matter around 1803. Whilst studying meteorology, Dalton concluded that evaporated water exists in air as an independent gas. Solid bodies can't occupy the same space at the same time, but clearly water and air could. If the water and air were composed of discrete particles, Dalton thought that evaporation might be viewed as a mixing of water particles ...view middle of the document...

3. Elements are characterized by the mass of their atoms. All atoms of the same element have identical weights, Dalton concluded. Atoms of different elements have different weights.With the discovery of isotopes, however, the claim was amended to read, "Elements are characterized by their atomic number".4. When elements react, their atoms combine in simple, whole-number ratios. This claim suggested a realistic strategy for determining relative atomic weights from elemental percentages in compounds.This effectively explained both the law of definite proportions and the law of multiple proportions.Some of the details of Dalton's original atomic theory are now known to be incorrect. But the core concepts of the theory (that chemical reactions can be explained by the union and separation of atoms and that these atoms have distinguishing properties) are the basis of modern physical science.JJ Thomson -Sir JJ Thomson was born in 1856, and is recognised as the British scientist who discovered and identified the electron. At the Cavendish Laboratory at Cambridge University, in 1897, Thomson was experimenting with currents of electricity inside empty glass tubes. He was investigating a long-standing puzzle known as "cathode rays". His experiments prompted him to make a bold proposal: these mysterious rays are streams of particles much smaller than atoms; they are in fact minuscule pieces of atoms. He called these particles "corpuscles," and suggested that they might make up all of the matter in atoms. It was startling to imagine a particle residing inside the atom--most people thought that the atom was indivisible, the most fundamental unit of matter.Thomson developed a model of an atom in which a number of negatively charged electrons were embedded in a sphere of positive electricity, with the two charges neutralising each other.Thomson's model of the atom is often referred to as the "plum pudding" model because it has a consistency that is all the same throughout the whole atom with a few plums to represent the tiny corpuscles. Thomson's model was widely accepted by people all over the world. It was such an amazing discovery that his...

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