2. Rutherford’s atomic model could not explain the chemical
properties of elements.
It only explains a few simple properties of atoms.
Niels Bohr, a Danish Physicist, improved Rutherford’s
model. He proposed that an electron is found only in
specific circular paths, or orbits, around the nucleus.
Bohr Model
1. Each possible electron orbit has a fixed energy called,
energy level.
2. An electron can move from one orbit to another if it
loses or gains energy.
in other words, if an electron gains energy, it will move to
the higher orbit and vice versa.
Go to page: 129
The required energy to move an electron from one energy
level to another is called, Quantum
3. Quantum Mechanical Model
It determines that allowed energies an electron can have and how
likely it is to find the electron in various locations around the
nucleus.
Erwin Schrodinger, an Austrian Physicist, improved the Bohr’s Model
He assumed that the probability of finding an electron within a certain
volume of space surrounding the nucleus can represented as a fuzzy cloud.
Atomic Orbital
A region of space in which there is a high probability of finding an
electron.
The energy levels of electrons in the quantum mechanical model
are labeled by principal quantum numbers (n), assigned as n =1, 2,
3, 4 and so forth.
Principal energy level consists of energy sublevels, s, p, d, f
And each energy sublevel is composed of orbitals, each orbital is
composed of maximum two electrons.
4. Principal
Energy Level
Number of Sublevels Type of Sublevel
Maximum Numbers of Electrons
Energy Level n Maximum number of electrons
n = 1
n = 2
n = 3
n = 4
2
1
4
3
1s (1 orbital)
2s (1 orbital), 2p (3 orbitals)
3s (1 orbital), 3p (3 orbitals), 3d (5 orbitals)
4s (1 orbital), 4p (3 orbitals), 4d (5 orbitals),
4f (7 orbitals)
1
2
3
4 32
18
8
2
6. Electron Configurations
The ways in which electrons are arranged in various orbitals
around the nuclei of atoms.
e electron configuration should follow three rules:
Aufbau Principle
Electrons occupy the orbitals of lowest energy first.
Pauli Exclusion Principle
An atomic orbital may describe at most two electrons,
and at the same orbital two electrons must have opposite
spins
Hund’s Rule
Electrons occupy orbitals of the same energy in a way that
makes the number of electrons with the same spin direction
as large as possible.
Which is lower in energy 4s orbital or 3d orbital??? Think !!!
7. Some actual electron configurations differ from those
assigned using the Aufbau principle because half filled
sublevels are not as stable as filled sublevels, but they are
more stable than other configurations.
If you have 3 electrons to fill p orbitals, how can you do it?
X
Go to page: 134, Table 5.3
Write the electron configuration for each following atoms:
a.Potassium b. Aluminum c. Copper
e.g.
