2The Battle of the two Philosophers… VS.AristotleDemocritus
3DEVELOPS THE IDEA OF THE ATOM. 460 BC Democritus – Greek ModelDEVELOPS THE IDEA OF THE ATOM.He pounds materials in his mortar and pestle until he reduces them to smaller and smaller particles which he ultimately calls…ATOMOS(greek for indivisible)
4Democritus – Greek Model Atoms are solid & homogeneousall atoms made of the same material.Different types of atoms have different shapes and sizes.The different shapes and sizes of the atoms determine the different properties of the substancesAtoms are infinite in number.
5Aristotle – Greek Model Earth, Fire, Air and Water approach to the nature of matter.All substances made of these four elementsBlend these in different proportions to get all substancesTransmute Lead into GOLD
6ARISTOTLE WINS!!!Democritus’ idea of “atoms” was ignored and forgotten for more than 2000 years!
8Dalton combines the idea of elements with that of atoms! HISTORY OF THE ATOMJohn Dalton - Billiard Ball Model (England)1808All matter is made up of tiny spheres called …ATOMSDalton combines the idea of elements with that of atoms!
9Dalton’s Atomic Theory Billiard Ball Model All elements are composed of atoms.indivisible and indestructibleAtoms of the same element are alikeAtoms of different elements are differentChemical reactions involve the rearrangement of atoms.
14J. J. Thomson (1898) Plum Pudding Model Thomson studied the passage of an electric current through a gas using cathode-ray tubes.As the current passed through the gas, it gave off rays of negatively charged particles.
19Thomson was surprisedIf 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!
20Thomson (1898) Plum Pudding Model Thomson called the negatively charged “corpuscles,” today known as electrons.He was unable to discover the positive charge that allows an atom to be neutral.
21J.J. Thomson (1898) Plum Pudding Model His model is called the “Plum Pudding” model.Atoms were made from a positively charged substance with negatively charged electrons scattered about, like raisins in a pudding.Plum Pudding
22Atoms are now considered divisible. Thank you J. J. !!Atoms are now considered divisible.
24Ernest Rutherford (1909) Nuclear Model Rutherford’s experiment Involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick)Was a Student of J.J. Thomson.
25Here’s what it looked like Rutherford’s experimentHere’s what it looked like
36Density and the AtomSince most of the particles went through, the atom was mostly emptyBecause the alpha particles deflected so much, the positive pieces in the core of the atom had to be very heavyPositive core had a small volume, big mass, big densityThis small dense positive area is the nucleus
37Ernest Rutherford (1909) Nuclear Model Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atom’s edge.He called the center of the atom the “nucleus”The nucleus is tiny compared to the atom as a whole.
39Niels Bohr (1913) Planetary Model In 1913, the Danish scientist Niels Bohr proposed an improvement. In his model, he placed each electron in a specific energy level.
40Niels Bohr (1913) Planetary 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 the nucleus.Each orbit contains a set number of electrons.
41Erwin Schrodinger (1926) Wave Model The exact location of an electron cannot be stated.Electrons are in regions called electron clouds.Atom mostly empty space
43Wave model No definite path for electron. Can only predict the odds of the location of the electron.
44James Chadwick (1931)Realized that the atomic mass of most elements was double the number of protons.Bombarded beryllium atoms with alpha particles.An unknown radiation was produced. Chadwick interpreted this radiation as being composed of particles with a neutral electrical charge and the approximate mass of a proton.This particle became known as the neutron.With the discovery of the neutron, an adequate model of the atom became available to chemists.
45Democritus & John Dalton Progression of the Atomic Model+-The structure of an atom, according to:Democritus & John DaltonJames ChadwickJ.J. ThomsonNeils BohrErnest RutherfordErwin Schrodinger
46Murray Gell-Mann & George Zweig (1964) Quantum Theory – Standard Model Gell-Mann found that all the elements of an atom are held together by quarks. To find this, he blasted high speed electrons into a hydrogen atom.Zweig proposed the existence of quarks.George Zweig
47Quarks – Quantum Theory- Standard Model Protons are made from 2 up quarks and 1 down quarkNeutrons are made from 1 up quark and 2 down quarks.