Rutherford Model
of the atom
According to
Rutherford and his gold foil experiment, the atom had a
positive, dense nucleus with the
electrons outside the nucleus.
He had no
In 1913 a new model of the atom was proposed by Niels Bohr
According to his theory, the electrons of an atom could only circle the
nucleus of the atom in allowed paths or orbits.
Bohr Model helps explains phenomena like metal glowing or fireworks
When energy is added to the electron, it gets “excited” and goes up to the next energy
level or orbit.
However, it does not stay there long, so it goes back down and when it does it
releases the energy that it gained
The energy given off
is usually in the form
of light which
explains the color
seen in fireworks,
light bulbs, glowing
metal that is heated,
Bohr measured the
energy given off by the
electrons and
determined the
distance of the orbits
(energy levels) from
Number of electrons in each orbit for
Bohr Model
•
Maximum of 2 electrons in 1
storbit or energy
level
•
Maximum of 8 electrons in 2
ndorbit or energy
level
•
Maximum of 8 electrons in 3
rdorbit or energy
level
•
Maximum of 18 electrons in 4
thorbit or
Bohr Model
Limitations
The problem with the Bohr model of the atom was that it only helped explain the behavior of the simple element
hydrogen. It could not explain the more
complex atoms after hydrogen.
What is an orbital????
An orbital is a 3 dimensional area in space
where an electron may be found. It does not
have a set pattern to it like in the Bohr Model of
the atom!
It is a cloud-like area around the nucleus where
the electron can be found 95% of the time.
Much like light, electrons have properties of
both a particle and a wave and do not travel in
a path like planets around a star or like any
other ordinary object that we as humans
The Heisenberg Uncertainty
Principle
This states that it is impossible to know both the position and velocity of an
electron at the with absolute precision. In other words, the more information you
have on one of these values, the less you know about the other!
So in an orbital (electron cloud) it is not possible to know exactly where an
electron is at any one moment. The orbital represents an area in space , the
Heisenberg Uncertainty Principle
Link
Another explanation of the behavior
of electrons is Schrödinger’s Cat –
how electrons do not behave like
ordinary particles we observe in
everyday life!
This electron
cloud model
of the atom is
often also
QUANTUM NUMBERS:
There are 4 different quantum numbers.
These quantum numbers help describe the
location of an electron around the nucleus of
the atom
Important Note:
No 2 electrons can have
the same 4 quantum numbers in an atom. If
they did it would indicate that they are
Principal Quantum Number
This quantum number
tells you the
energy level in
which the electron
is located.
Angular Momentum Quantum
Number
•
The angular momentum quantum
The four types of orbital
shapes:
The 4 types of orbitals are called:
s, p, d and f
s orbitals are spherical in shape:
Orbital shapes
video
Magnetic Quantum Number
•
The magnetic quantum number
shows the orientation of the
Spin Quantum Number
•
Spin quantum number denotes the
behavior (direction of spin) of an
electron within a magnetic field.
•
Possibilities for electron spin:
4.3 Electron Configuration
3 rules for adding electrons to orbitals
1. Aufbau principle: an electron will always
occupy the lowest-energy orbital available
2. Pauli exclusion principle: no two electrons in
the same atom can have the same set of four
quantum numbers
3. Hund’s rule: orbitals of equal energy are each
occupied by one electron before any orbital is
occupied by a second electron, and all
Electron Configuration
Electron configuration is
how the electrons are
arranged in their orbitals
around the nucleus of the
Maximum number of
electrons in each sublevel:
s orbital: 2 electrons
p orbital: 6 electrons
d orbital: 10 electrons
•
Electron configuration of the
Octet
When an element has its outermost s and p
orbitals filled – s
2p
6– it has a total of 8
electrons, known as an octet.
The noble gas elements have octets –
they are chemically unreactive because
NOBLE GAS SHORTCUT FOR
ELECTRON CONFIGURATION
Especially for elements that
have many electrons:
Example:
