history of the atom 440 bc – democritus and leucippus developed the original atomic concept...
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History of the AtomHistory of the Atom• 440 BC – Democritus and Leucippus
developed the original atomic concept– There exist indivisible particles
called atoms (“a” meaning not; “tomos” meaning cut
• There exist empty space between atoms
• Atoms are completely solid• Atoms are homogeneous with no
internal structure• Atoms differ in size, shape and weight
• 440 BC – Democritus and Leucippus developed the original atomic concept– There exist indivisible particles
called atoms (“a” meaning not; “tomos” meaning cut
• There exist empty space between atoms
• Atoms are completely solid• Atoms are homogeneous with no
internal structure• Atoms differ in size, shape and weight
1789 Antoine Lavoisier1789 Antoine Lavoisier
• Law of conservation of matter – matter can be neither created nor destroyed, merely changed from one form to another
• Law of conservation of matter – matter can be neither created nor destroyed, merely changed from one form to another
1800’s Joseph Proust1800’s Joseph Proust
• Law of Definite Proportions
• Observed that specific substances always have the same ratio by mass
• Law of Definite Proportions
• Observed that specific substances always have the same ratio by mass
1808 John Dalton – Atomic theory explains and verifies the Law of
Conservation of Matter
1808 John Dalton – Atomic theory explains and verifies the Law of
Conservation of Matter• Theory of atoms
–All elements are made up of tiny particles called atoms
–The atoms of a given element are identical, but are different from any other element
–Atoms of different elements combine to form compounds
• Theory of atoms–All elements are made up of
tiny particles called atoms–The atoms of a given
element are identical, but are different from any other element
–Atoms of different elements combine to form compounds
–A given compound always has the same relative number and types of atoms
–In a chemical reaction atoms are reorganized, resulting in changes in the way they are bound together; the atoms themselves are not changed
–A given compound always has the same relative number and types of atoms
–In a chemical reaction atoms are reorganized, resulting in changes in the way they are bound together; the atoms themselves are not changed
1810 John Dalton1810 John Dalton
• Law of Multiple Proportions–Elements in a compound
combine in whole number ratios by mass• Thus he says atoms react as
whole units
• Law of Multiple Proportions–Elements in a compound
combine in whole number ratios by mass• Thus he says atoms react as
whole units
1859 – Julius Plucker1859 – Julius Plucker
• Sealed gases in tubes with electrodes on each end to form the cathode ray tube–One end – the anode – was
positively charged, thus attracted negative ions
–The other end – the cathode – was negatively charged, thus attracted positive ions
• Sealed gases in tubes with electrodes on each end to form the cathode ray tube–One end – the anode – was
positively charged, thus attracted negative ions
–The other end – the cathode – was negatively charged, thus attracted positive ions
1897 JJ Thomson1897 JJ Thomson• Used a cathode ray tube with a
beam that glowed between the electrodes when they were connected to an electrical charge – traveling from the cathode to the anode
• The beam was attracted to a positive charge, leading Thomson to propose that there were small negatively charged particles that he called electrons
• Used a cathode ray tube with a beam that glowed between the electrodes when they were connected to an electrical charge – traveling from the cathode to the anode
• The beam was attracted to a positive charge, leading Thomson to propose that there were small negatively charged particles that he called electrons
1907 JJ Thomson1907 JJ Thomson
• Develops the “plum pudding” model of the atom–A sphere of positive
electricity (the pudding) with electrons (the plum bits) scattered in it
• Develops the “plum pudding” model of the atom–A sphere of positive
electricity (the pudding) with electrons (the plum bits) scattered in it
1906 Ernst Rutherford1906 Ernst Rutherford
• Announced that alpha particles can be scattered by air
• Discovers the presence of the nucleus
• Announced that alpha particles can be scattered by air
• Discovers the presence of the nucleus
1913 Robert Millikan1913 Robert Millikan
Determined the charge to mass ratio of the electron
Determined the charge to mass ratio of the electron
1913 Neils Bohr1913 Neils Bohr
Working with Rutherford proposed the planetary model of the atom
Working with Rutherford proposed the planetary model of the atom
Late 1910’sLate 1910’sBased on earlier work by E.
Goldstein (1886) Millikan, Thomson and coworkers proposed the presence of a positively charged particle called the protonGoldstein observed what he called
canal rays while using a cathode ray tube with the rays traveling in the opposite direction of Thomson’s
Based on earlier work by E. Goldstein (1886) Millikan, Thomson and coworkers proposed the presence of a positively charged particle called the protonGoldstein observed what he called
canal rays while using a cathode ray tube with the rays traveling in the opposite direction of Thomson’s
1920 Rutherford1920 Rutherford
Proposes the presence of a third particle, found in the nucleus when the total mass of the atom cannot be attributed to the proton and electron
Proposes the presence of a third particle, found in the nucleus when the total mass of the atom cannot be attributed to the proton and electron
1932 James Chadwick
1932 James Chadwick
Finds high energy particles with essentially the same mass as a proton and no charge – the neutron
Finds high energy particles with essentially the same mass as a proton and no charge – the neutron
1924 Wolfgang Pauli1924 Wolfgang Pauli
States the quantum exclusion principleNo two particles can occupy
the same position at the same time in an atom
States the quantum exclusion principleNo two particles can occupy
the same position at the same time in an atom
1926 Werner Heisenberg
1926 Werner Heisenberg
Proposes a theory of the movement of electrons in the atom – matrix mechanics
States it is impossible to accurately predict both the position and the momentum of any object (including an electron) at the same time – the Heisenberg uncertainty principle
Proposes a theory of the movement of electrons in the atom – matrix mechanics
States it is impossible to accurately predict both the position and the momentum of any object (including an electron) at the same time – the Heisenberg uncertainty principle
1926 Erwin Schrodinger1926 Erwin Schrodinger
Developed the wave equation to explain electron activity
Considered the electron’s behavior as like that of a wave rather than a particle
Developed the wave equation to explain electron activity
Considered the electron’s behavior as like that of a wave rather than a particle
1926 Max Born1926 Max Born
Suggested that the wave function of the Schrodinger equation was a measure of the probability of finding an electron at a given location
Suggested that the wave function of the Schrodinger equation was a measure of the probability of finding an electron at a given location
Quantum Mechanical Model of the Atom
Quantum Mechanical Model of the Atom
Based on Shrodinger’s wave equation, describes the electrons as a cloud surrounding the nucleusThe higher the energy of the
electron, the further it can travel from the nucleus
Based on Shrodinger’s wave equation, describes the electrons as a cloud surrounding the nucleusThe higher the energy of the
electron, the further it can travel from the nucleus