Presentation on theme: "(greek for indivisible)"— Presentation transcript:
1(greek for indivisible) HISTORY OF THE ATOMDemocritus develops the idea of atoms460 BChe pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he calledATOMA(greek for indivisible)
2HISTORY OF THE ATOM ATOMS John Dalton 1803 suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called themATOMS
3HISTORY OF THE ATOM ELECTRON Joseph John Thompson 1898 found that atoms could sometimes eject a far smaller negative particle which he called anELECTRON
4HISTORY OF THE ATOM Ernest Rutherford 1910 oversaw Geiger and Marsden carrying out his famous experiment.they fired Helium nuclei at a piece of gold foil which was only a few atoms thick.they found that although most of them passed through. About 1 in 10,000 hit
5HISTORY OF THE ATOMgold foilhelium nucleihelium nucleiThey found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back.
6HISTORY OF THE ATOMRutherford’s new evidence allowed him to propose a more detailed model with a central nucleus.He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attractionHowever, this was not the end of the story.
7HISTORY OF THE ATOM Niels Bohr 1913 studied under Rutherford at the Victoria University in Manchester.Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.
8Bohr Atom The Planetary Model of the Atom Objectives: To describe the Bohr model of the atom.To explain the relationship between energy levels in an atom and lines in an emission spectrum.
9Development of Atomic Models Thomson modelIn the nineteenth century, Thomson describedthe atom as a ball of positive charge containinga number of electrons.Rutherford modelIn the early twentieth century, Rutherfordshowed that most of an atom's mass isconcentrated in a small, positively chargedregion called the nucleus.Bohr modelAfter Rutherford's discovery, Bohr proposedthat electrons travel in definite orbits aroundthe nucleus.Quantum mechanical modelModern atomic theory described theelectronic structure of the atom as theprobability of finding electrons withincertain regions of space.
11Quantum Mechanical Model Niels Bohr &Albert EinsteinModern atomic theory describes the electronic structure of the atom as the probability of finding electrons within certain regions of space (orbitals).
15ATOMIC STRUCTUREParticleChargeMassproton+ ve charge1neutronNo charge1electron-ve chargenil
16number of electrons = number of protons ATOMIC STRUCTUREHe2Atomic numberthe number of protons in an atomAtomic mass (mass number)the number of protons andneutrons in an atomnumber of electrons = number of protons
17ATOMIC STRUCTUREElectrons are arranged in Energy Levels or Shells around the nucleus of an atom.first shell a maximum of 2 electronssecond shell a maximum of 8 electronsthird shell a maximum of 8 electronsValence shell – the outermost shell of an atomthat contains electrons
181. Electron Configuration ATOMIC STRUCTUREThere are two ways to represent the atomic structure of an element or compound;1. Electron Configuration2. Dot & Cross Diagrams
19ELECTRONIC CONFIGURATION With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example;Nitrogenconfiguration = 2 , 572 in 1st shell5 in 2nd shellN= 714
20ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements;20118NaOCaa)b)c)2316402,8,8,22,8,12,617145ClSiBd)e)f)3528112,8,72,8,42,3
21N DOT & CROSS DIAGRAMS Nitrogen With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example;XNitrogenN7XXNXX14XX
22DOT & CROSS DIAGRAMS O Cl Draw the Dot & Cross diagrams for the following elements;X817XOCla)b)XX1635XXXXXClXXXXXXXOXXXXXXXXXX
23SUMMARY The Atomic Number of an atom = number of protons in the nucleus.The Atomic Mass of an atom = number ofProtons + Neutrons in the nucleus.The number of Protons = Number of Electrons.Electrons orbit the nucleus in shells.Each shell can only carry a set number of electrons.