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C1 (History (Ernest Rutherford (1909, Fired alpha particles at thin gold…
C1
History
Democritus
Atoms are smallest part of object
Smal solid sphere
Indestructible & indivisible
John Dalton
1803
Elements are 'pure'
All atoms have same mass
Different elements contained different atoms
J.J. Thomson
1897
Plum pudding model
Cathode rays (-ve) changed direction is electric fields
Atoms contain electrons
Atoms are neutral overall
Ernest Rutherford
1909
Fired alpha particles at thin gold foil
Some were deflected
Positive nucleus that contained most of the mass
Geiger & Marsden
Electrons orbitting
Niels Bohr
1913
Electrons would spiral into nucleus (+ve & -ve)
Electrons occupy fixed energy levels
Can jump between orbits
Atom
Definitions
atom
- smallest particle of an element that has the chemical properties
molecule
- two or more atoms joined by chemical bonds
element
- contains one type of atom
compound
- contains two or more elements
Isotopes
Versions that have different numbers of neutrons
Same chemical properties (same number of electrons)
Different physical properties
Named after mass number
Parts
Proton
Charge: +1
Relative mass: 1
Neutron
Charge: 0
Relative mass: 1
Electron
Charge: -1
Relative mass: 0.0005
Ions
Charged particle
Atom loses/gains electrons
Particle model
States
Solid
Regular arrangement
Particles close together
Vibrate about fixed positions
Liquid
Random arrangement
Particles close together (always touching)
Move around each other
Gas
Random arrangement
Particles far apart
Move quickly in all directions
Changes
Physical
Changes shape/size
No new substances made
Can normally be reversed
Particles rearranged
Chemical
One or more substances produced
Properties different from original substance
Difficult/impossible to reverse
Particles break up, components rearranged
Limitations
Size
Atoms are extremely small
e.g. hellium atom is 62pm (6.2x10⁻¹³)
Space
Distance between atoms much larger than diameter
e.g. distance between helium atom 55 times larger than diameter
Forces
Electrostatic forces
of attraction bewteen particles
Between negative & positive charges
Not shown in models