NIELS BOHR
•
(1885-1962)
• Worked w/ Rutherford
• Agreed that atom had nucleus surrounded by large
volume of space
4.3 MODERN ATOMIC THEORY
Bohr’s Model: describes the arrangement of electrons in
an atom
The electrons move in spherical orbits at fixed distances
from the nucleus
Electrons are arranged in Energy Levels and only a
certain number of electrons may occupy each energy
level
HOW TO DRAW ATOMS
Bohr Model - electrons
move around the
nucleus in orbits or
energy levels
 Like planets around sun
ENERGY LEVELS
• Different levels have different energies
• Can lose or gain energy and change levels
• Levels closest to nucleus are lowest energy
(less likely to be used in bonding)
ENERGY LEVELS
Electrons can move from one energy level to another when an
atom loses or gains energy
All atoms have 2 electrons in their 1st energy level (level closest to
the nucleus)
2nd level = 8
The levels closest to the nucleus has the strongest attraction or
bonds
The last energy level of any atom has a maximum of 8 electrons
HOW TO DRAW ATOMS
Many energy levels:
 1st -max of 2 e 2nd -max of 8 e 3rd - max of 18 e-
Must fill up in order
VALENCE ELECTRONS
• Electrons in
outermost shell are
called valence
electrons
• Ex: Carbon has 4
valence electrons,
but 6 total electrons
BOHR MODEL OF ATOMS & ENERGY
LEVELS
MODERN ATOMIC MODEL
• Today use electron cloud model
• Electron cloud shows most probable location
of e• Cloud is thicker where e- more likely to be
• Like ceiling fan or propeller on plane
ELECTRON CLOUD MODEL
ELECTRON CLOUD MODEL