Presentation on theme: "Atoms and their structure"— Presentation transcript:
1 Atoms and their structure Chapter 2Atoms and their structure
2 History of the atom Original idea of the atom: Ancient Greece (400 B.C.)Greek philosophers Democritus and LeucippusEmpty space and small particles
3 The Beginning of Atomic Theory Atomos - not to be cut, indivisibleAtoms - smallest particles of matter, different types of atoms exist for every type of matter
4 Lavoisier French chemist (1743-1794) Observed chemical changes in sealed containersMass of reactants = Mass of productsConservation of Matter
5 Who’s Next? John Dalton: A teacher in Late 1700’s England Summarized results of his experiments and those of other’s in:Dalton’s Atomic TheoryCombined ideas of elements with that of atoms
6 Dalton’s Atomic Theory 1. All matter is made of tiny particles called atoms.2. Atoms are indestructible and cannot be divided into smaller parts.3. Atoms of the same element are identical, those of different atoms are different.
7 Theory or Law? A scientific law is a fact of nature Ex: the sun rises, conservation of matterA theory explains the lawDalton’s theory explains why matter in conserved
8 Parts of Atoms J. J. Thomson - English physicist, 1897 Cathode ray tube experiment.Vacuum tube - all air has been pumped out.
13 - + Thomson’s Experiment Voltage source Passing an electric current makes a beam appear to move from the negative to the positive end
14 - + Thomson’s Experiment Voltage source Passing an electric current makes a beam appear to move from the negative to the positive end
15 - + Thomson’s Experiment Voltage source Passing an electric current makes a beam appear to move from the negative to the positive end
16 - + Thomson’s Experiment Voltage source Passing an electric current makes a beam appear to move from the negative to the positive end
17 Thomson’s ExperimentVoltage sourceBy adding an electric field
18 Thomson’s ExperimentVoltage source+-By adding an electric field
19 Thomson’s ExperimentVoltage source+-By adding an electric field
20 Thomson’s ExperimentVoltage source+-By adding an electric field
21 Thomson’s ExperimentVoltage source+-By adding an electric field
22 Thomson’s ExperimentVoltage source+-By adding an electric field
23 Thomson’s Experiment Voltage source + - By adding an electric field he found that the moving pieces were negative
24 Thomson’s Model Found the electron Couldn’t find positive charge(for a while)Said the atom was like plum puddingA bunch of positive stuff, with the electrons able to be removed
25 Other Subatomic Particles Proton - positively charged particles1,840 times heavier than the electronNeutron - no charge, but the same mass as a proton.Where are the particles?
26 Rutherford’s Experiment Ernest Rutherford - English physicist, (1910)Used radioactivityAlpha particles - positively charged He nuclei given off by poloniumShot them at gold foilwhich can be made afew atoms thick
38 Subatomic Particles Relative mass Actual mass (g) Name Symbol Charge Electrone--11/18409.11 x 10-28gProtonp++111.67 x 10-24gNeutronn011.67 x 10-24g
39 Structure of the Atom There are two regions: 1. The nucleus - protons and neutrons- positive charge- almost all the mass2. Electron cloud- Most of the volume of an atom- The region where the electron can be found
40 Counting the Pieces Atomic Number = number of protons # of protons determines kind of atomthe same as the number of electrons in the neutral atomMass Number = the number of protons PLUS the number of neutronsIncludes all the things with mass
41 Isotopes Dalton was incorrect. Atoms of the same element can have different numbers of neutrons!different mass numberscalled isotopes
42 Periodic Table InfoContains the symbol of the element, the atomic mass and the atomic numberSymbol: letters in the middleAtomic mass: decimal number (usually at bottom)Atomic number: whole number (usually at top)
43 Periodic Table InfoLabel the following diagram:
44 Atomic Mass How heavy is an atom of oxygen? There are different kinds of oxygen atoms.Look at Average atomic mass.Based on abundance of each element in nature.
45 Atomic MassCalculate the atomic mass of copper if copper has two isotopes.69.1% of Cu atoms have a mass of amu and the rest have a mass of amu.
46 Bohr’s Model Why don’t electrons fall into the nucleus? Move like planets around the sun.Circular orbits at different levels.Amounts of energy separate one level from another.
48 } Bohr’s Model Fifth Fourth Increasing energy Third Second First Further away from the nucleus means higher energy.There is no “in between” energyEnergy LevelsFifthFourthThirdIncreasing energySecondFirstNucleus