Download The Bohr Model

The Bohr Model
Atomic Models
This is the Bohr model.
In this model, the
nucleus is orbited by
electrons, which are
in different energy
levels.
Bohr Model
• According to Bohr’s
atomic model,
electrons move in
definite orbits
around the nucleus,
much like planets
circle the sun. These
orbits, or energy
levels, are located at
certain distances
from the nucleus.
The Wave Model
• Today’s atomic
model is based on
the principles of
wave mechanics.
• According to the
theory of wave
mechanics, electrons
do not move about
an atom in a definite
path, like the planets
around the sun.
The Wave Model
• In fact, it is impossible to determine the exact
location of an electron. The probable location of an
electron is based on how much energy the electron
has.
• According to the modern atomic model, at atom has
a small positively charged nucleus surrounded by a
large region in which there are enough electrons to
make an atom neutral.
Electron Cloud:
• A space in which
electrons are likely to
be found.
• Electrons whirl about
the nucleus billions of
times in one second
• They are not moving
around in random
patterns.
• Location of electrons
depends upon how
much energy the
electron has.
Electron Cloud:
• Depending on their energy they are locked into a
certain area in the cloud.
• Electrons with the lowest energy are found in the
energy level closest to the nucleus
• Electrons with the highest energy are found in the
outermost energy levels, farther from the nucleus.
Drawback
• Bohr’s theory did not
explain or show the
shape or the path
traveled by the
electrons.
• His theory could only
explain hydrogen and
not the more complex
atoms
Increasing energy
Fifth
Fourth
Third
Second
First
• Further away
from the
nucleus means
more energy.
• There is no “in
between”
energy
• Energy Levels
The Quantum Mechanical Model
• Energy is quantized. It comes in chunks.
• A quanta is the amount of energy needed to move
from one energy level to another.
• Since the energy of an atom is never “in between”
there must be a quantum leap in energy.
• Schrödinger derived an equation that described the
energy and position of the electrons in an atom
Atomic Orbitals
• Principal Quantum Number (n) = the energy level
of the electron.
• Within each energy level the complex math of
Schrödinger's equation describes several shapes.
• These are called atomic orbitals
• Regions where there is a high probability of
finding an electron
S orbitals
• 1 s orbital for
every energy level
1s
2s
3s
• Spherical shaped
• Each s orbital can hold 2 electrons
• Called the 1s, 2s, 3s, etc.. orbitals
P orbitals
•
•
•
•
Start at the second energy level
3 different directions
3 different shapes
Each orbital can hold 2 electrons
• The p Sublevel has 3 p
orbitals
The D sublevel contains 5 D orbitals
• The D sublevel starts in the 3rd energy level
• 5 different shapes (orbitals)
• Each orbital can hold 2 electrons