The Nature of
Electrons
• Scientists noticed when
certain elements are placed
in a flame, they emit light!
• The light given off when an
element is heated is called
it’s atomic emission
spectrum
• The atomic emission
spectrum is a different
color for every element!
• The color is like the
“signature” of that element
• It can be used to identify
the element like a
fingerprint can identify you!
No two elements have
the same atomic emission
spectrum!!!
Scientists began to
wonder . . .
• Rutherford’s model is
good, but it doesn’t
explain some things
Rutherford’s model didn’t explain:
1. why different elements
react differently (and have
different atomic emission
spectra)
2. how electrons are arranged
Neils Bohr
• Bohr worked with hydrogen
and developed a new model
of the atom:
The Planetary Atomic Model
Bohr’s Planetary Atomic Model:
• electrons move around the
nucleus in circular “orbits”
(paths) much like planets
orbit the sun
• Each “orbit” has a certain
level of energy
smaller orbits = lower energy
larger orbits = higher energy
Energy . . . yeah baby!
• electrons are able to change
energy levels one at a time
(like climbing the rungs of a
ladder)
• The LOWEST energy level
available is called the ground
state (it is the closest to the
nucleus)
• As an electron “jumps” from a
low energy level to a higher
one, it needs to absorb energy
and become “excited”
• like you would need energy to
“jump” up high!
electron that absorbed
energy and is “excited”
ground state
nucleus
• once an electron is
“excited” and in a higher
energy level, it can’t stay
there because it’s not the
“home orbit”
• An electron will “drop” to a
lower energy level
• Every time an electron drops
levels, it emits light – this is
the light that we see when we
put an element into a flame!
• The electrons release the
energy before they go “home”
electron in ground state
that emitted light energy
nucleus
Bohr worked to discover all
of this, but keep in mind
that he only worked with
hydrogen!
Scientists thinkin’ again . . .
• If opposite charges attract,
then why are negative
electrons (that are lighter)
not pulled into the positive
nucleus?????
• Well . . . It all has to do with
energy – the energy of motion!
• electrons actually “wiggle” as
they move around the nucleus
DeBroglie’s Wave Theory
• DeBroglie proposed that
electrons move like waves
around the nucleus
Heisenberg
Heisenberg’s Uncertainty
Principle: it is impossible to
know the exact position of
an electron (if they travel in
waves)
The Quantum Mechanical Model
1. developed by Schrödinger
2. atoms have a dense,
positively charged nucleus
3. electrons surround the
nucleus and are treated as
waves, not particles
4. There is a GOOD probability
of finding an electron in an
atomic orbital
**an atomic orbital is a threedimensional region around the
nucleus (it’s not an orbit)
You made it!
Was it the worst day
of your life?