When was the Greek atom theorised?
500BCE
Who developed the first idea for the atom?
Greek philosopher Democritus
What did Democritus suggest about the atom?
• Matter can only be divided certain number of times until you end up with a particle not able to be split further
• Called ‘átomos’
What does átomos mean?
Greek for invisible
When did Dalton develop his atomic theory?
Early 1800’s
What was Dalton’s atomic theory?
• Atoms are tiny particles making up elements
• Atoms can’t be divided
• All atoms of a given element are equal
• Atoms of one element are different from those of others
From Dalton’s atomic theory, what did he do?
• Used own symbols to represent different element atoms
• Developed first table of atomic masses
• Some predictions still hold truth and used in modern chemistry
When did J.J Thompson discover electrons?
1897-1906
How were cathode rays produced in J.J Thompson’s discovery of electrons?
Emitted from cathode ray tubes
What were the properties of cathode rays?
• Negative charge
• Could be deflected by both a magnet and electric field
• Have very, very small mass
What were cathode rays found to be?
Electrons
Where did J.J Thompson conclude electrons came from?
Within atoms of electrodes
What did J.J Thompson disprove about the ancient Greek theory of the atom?
An atom couldn’t be split any further
What did J.J Thompson propose about the atomic structure?
Atoms are made of negative electrons moving around in a positive charge ‘sea’, commonly called ‘plum-pudding model’
How did J.J Thompson’s atomic model have a charge of 0?
Overall negative charge was equal to overall positive charge
When did Rutherford perform the gold-leaf experiment?
1909-1911
Who were Rutherford’s students helping with the gold-leaf experiment?
Hans Geiger and Ernest Marsden
How did Rutherford’s perform his gold-leaf experiment?
• Directed α-particles towards very thin gold foil sheet, measuring any deflection
• Calculated ‘plum-pudding model’ would hardly deflect α-particles
What were the results from Rutherford’s gold-leaf experiment?
• Most particles didn’t deflect, as expected
• A small percentage deflected through large angles
• Very few deflected back towards source
How did Rutherford propose his idea of the atom and disprove the ‘plum-pudding model’?
• Atom’s positive charge and most mass are concentrated in nucleus at centre
• Electrons orbit nucleus like planets orbiting Sun
• Most atoms volume is space between nucleus and orbiting electrons
• Overall positive and negative charges must balance
When did Niels Bohr propose the planetary model and when did Henry Moseley work on atomic numbers?
1913
How did the Danish physicist Niels Bohr alter Rutherford’s model of the atom?
Allow electrons to follow only certain paths
Why did Niels Bohr alter Rutherford’s atomic model?
Otherwise electrons would spiral into nucleus
What did Bohr’s model help explain?
• Spectral lines seen in emission spectra
• Electron energy at different distances from nucleus
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The Changing Atom32
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Atomic Structure6
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Atomic Masses11
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Determining Masses Using Mass Spectrometry5
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Ions and The Periodic Table4
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Amount of Substance and the Mole10
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Types of Formulae6
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Moles and Gas Volumes18
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Moles and Solutions11
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Chemical Equations6
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Moles and Reactions4
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Percentage Yields5
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Atom Economy9
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Acids and Bases17
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Salts12
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Formulae for Crystals and Salts8
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Titrations14
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Oxidation Numbers6
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Redox Reactions8
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Shells and Orbitals19
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Sub-Shells and Energy Levels7
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An Introduction to Chemical Bonding3
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Ionic Bonding4
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Structures of Ionic Compounds3
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Covalent Bonding3
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Dative Covalent Bonding12
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Structures of Covalent Compounds8
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Shapes of Molecules and Ions11
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Electronegativity and Bond Polarity7
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Intermolecular Forces16
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Hydrogen Bonding12
