Modern Atomic Theory and
Electrons
Chapter 4 Section 3
Energy Levels
We already know that in Bohr’s model,
electrons move at a constant speed around
the nucleus like planets moving around the
sun.
 Each atom has energy. If an atom gains or
loses energy, the energy of the electron can
change.
 Energy Levels- The possible energies that
electrons in an atom can have.
 An electron in an atom can move from one
energy level to another when the atom gains or
loses energy.

Think of Energy Levels Like a
Staircase:
Just like you can’t stand in between stairs,
electrons cannot exist between energy levels.
 The bottom stair is like the lowest energy level,
and each step up represents a higher energy
level.
 The distance between two steps represents the
difference in energy between the energy levels
 No two elements have the same set of energy
levels.

Electron Cloud Model
*The movement of electrons between
energy levels explains the light you see
when fireworks explode!!!!!*
 Electrons do in fact move more
unpredictably then the planets in the solar
system.
 An electron cloud is a visual model of
the most likely locations for electrons
around the nucleus of an atom.

Electron Cloud Model
Atomic Orbitals
The electron cloud represents all the
orbitals in the atom.
 An orbital is a region of space around the
nucleus where an electron is found.
 An electron cloud is a good
approximation of how electrons behave in
their orbitals.

Atomic Orbitals
The lowest energy level has only one
orbital, and higher energy levels have
more than one orbital.
 Each orbital can contain two electrons at
most.

Energy Level
Number of Orbitals
Max. # of electrons
1
1
2
2
4
8
3
9
18
4
16
32
Electron Configurations
An electron configuration is the
arrangement of electrons in the orbitals
of the atom.
 The most stable electron configuration is
where the electrons have the lowest
possible energies.
 When an electron has the lowest possible
energy, it is said to be in its ground state.
