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Development of the Atomic Theory
• Dalton – All matter is made of atoms
• Rutherford – His alpha particle experiment
discovered the dense nucleus
• JJ Thompson – “Plum pudding Model” –
discovered the electron
• Bohr – Said electron travel in distinct orbits or
energy levels around the nucleus
• Mendeleev – Organized elements by
properties to make the periodic table
Bohr model of the atom
Electron Configuration
Bohr’s proposal that electrons travel in defined
orbits around the nucleus was abandoned as
quantum mechanics was developed!
According to quantum mechanics the definition
of an orbital is an area of space where there is a
high probability of finding an electron.
Look in your data booklet at the
electron configuration chart!
• An energy level (n) is a specific amount of energy
which an electron in an atom can possess
• A quantum of energy is the difference in energy
between two energy levels
• A shell is all orbitals of electrons in one energy
level (n value)
• Each shell contains subshells which are a set of
orbitals of the same type
• Each orbital can hold two electron (each spinning
in a different direction
S- orbital (There is one s orbital per
energy level)
P- orbitals – There are three “p”
orbitals per energy level starting in
level 2
D- orbitals – There are five “d” orbitals per
energy level starting in level 3
Ground State Electron Configurations
P
Ti
Co
Core Notation
S
Rb
Kr
Electron Configurations of Ions
• Na+
• Sr +2
• N -3