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01 Atomszerkezeti ismeretek

2014.04.09

 

The Structure of the Atom
 
Theories
·         Democritus: all substances are made of atoms (special, indestructible, could not be split up)
·         Aristoteles: 4 elements (earth, air, water, fire)
·         Dalton: list of chemical elements: 1 element is made of 1 type of atoms
·         Rutherford: alpha particles to a thin gold foil – 1 in 10 000 particles bounced back – dense nucleus at the centre, electrons flying around the nucleus
·         Bohr: electrons on orbits (fixed energies)
 
The Atom:
Diameter: 10-10 m
Nucleus: 10-15 m
Nucleons (particles in the nucleus):
·         Proton (p+, positive charge, relative mass=1)
·         Neutron (n0, no charge, relative mass=1)
Electron cloud:
·         Electron (e-, negative charge, mass=1/1840
Nucleus: can not be changed in chemical reactions (very strong nuclear forces)
Atomic number (Z): proton number (1H, 6C)
Mass number (A): proton number + neutron number (1H, 12C)
Isotopes: Atomic number is the same but mass number is different (612C, 614C)
Relative atomic mass: an average atom mass of the element is compared to the 1/12 of the mass of the 612C atom
Mole: 6x1023 atoms
Molar mass: the mass of 1 mole of particles
 
Radioactivity
Radioactive atoms: nucleus is not stable, it decomposes, radioactive radiation is emitted
·         α radiation: 2p+, 2no
·         β radiation: e-
·         γ radiation: electromagnetic radiation
Radioactivity in use
·         Diagnostics (iodine isotope)
·         Treatment (killing of cancer)
·         Radiocarbon dating (C14 isotope, half life = 5700 years)
Nuclear energy
Chain reaction
235U + neutron = 92Kr + 142Ba + neutrons
Energy content: 1 g 235U = 2.5 tonns of coal
Atomic force in use
Atomic bomb
Nuclear power station
Regulated nuclear fissing (chain reaction)
Uranium fuel rods
Control rods: boron, cadmium, graphite (neutron absorber)
 
Electron structure
Orbital: the space where an electron can be found in 90% of probability
Shell: orbitals are at the same distance from the nucleus
Subshell: orbitals with the same shape
Subshells

Shape
Directions
Sizes
s
Spherical
1
7 (1s…7s)
p
Axial
3
6 (2p…7p)
d
2 x axial
5
5 (3d…7d)
f
3 x axial
7
4 (4f…7f)

 
Rules
Energy minimum: electrons will fill the lowest energy orbitals first
Pauli Exclusion Principle: an orbital can hold 0, 1, or 2 electrons only
Hund’s Rule: when filling subshells electrons are placed in individual orbitals before they are paired up