Transcript quantum mechanical model

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Calculating Average Atomic Mass
Worksheet
YWBAT
• Describe what Bohr proposed in his model of
the atom.
• Describe what the quantum mechanical
model determines about the electrons in an
atom.
• Explain how sublevels of principal energy
levels differ
Revising the Atomic Model
• Rutherford’s atomic model could not explain
the chemical properties of elements.
• For example, why does iron first glow dull red,
then yellow, then white when heated to
higher and higher temperatures?
The Bohr Model
• Niels Bohr (1913)
• Incorporated discoveries about how the
energy of atoms changes when the atom
absorbs or emits light.
• Stated that the electrons orbit the nucleus like
planets orbit the Sun.
The Bohr Model
• Each possible electron orbit has a fixed energy
known as an Energy Level
Quantum of Energy
Amount of energy
required to move an
electron from one
energy level to another
The Bohr Model
Bohr’s model can be compared to rungs of a
ladder.
• Electrons cannot exist between
energy levels
• The energy levels in atoms are
unequally spaced (higher energy
levels are closer together)
The Bohr Model
• When an electron occupies the lowest
possible energy level it is said to be in its
ground state.
• An electron can absorb energy (become
excited) from an external source:
– Sun
– Fire (heat)
– Electricity
The Bohr Model
• When electrons absorb energy, they can jump
to higher energy levels. This is called the
excited state.
• When the electron returns to the ground
state, it releases energy in the form of light.
Emission
Line
Spectra
The Bohr Model
• Scientists began wondering why the electron
had to be in a specific orbit.
• This led to the Heisenberg Uncertainty
Principle which states:
At a given instant in time, it is impossible to
determine both the position and the velocity of
an electron
Quantum Mechanical Model
• Erwin Schrodinger developed and solved a
mathematical equation describing the
behavior of the electron in a hydrogen atom.
• The modern description of electrons, the
quantum mechanical model, came from the
solutions to the Schrodinger equation.
Quantum Mechanical Model
• The probability of finding an electron is
represented as a fuzzy cloudlike region.
• The cloud is more dense where the probability
of finding the electron is high.
Atomic Orbital – region of space
where there is a high probability
of finding an electron
Quantum Numbers
Used to specify properties of atomic orbitals and
electrons in orbitals:
1.
2.
3.
4.
Principle quantum number (n)
Angular momentum number (l)
Magnetic quantum number (ml)
Spin quantum number (ms)
Principle Quantum Numbers (n)
• Indicates the main energy level (shell)
occupied by the electron
• Assigned values n=1,2,3,4,5,6,…
• Energy level corresponds to the period (row)
of the periodic table
– 1st energy level = first period (n=1)
– 2nd energy level = second period (n=2)
Angular Quantum Numbers (l)
• Indicates the shape of the orbital
• L = s,p,d,f
• Often called the sublevel
Sublevel
The number of sublevels within a principal
energy level is always equal to the principal
quantum number
# sublevels = principal quantum number
For example,
n=1 has 1 sublevel (s)
n=2 has 2 sublevels (s & p)
Sublevel
There can be several orbital configurations
within a sublevel (i.e., s,p,d,f).
S - sublevel contains 1 orbital
P - sublevel contains 3 orbitals
D - sublevel contains 5 orbitals
F - sublevel contains 7 orbitals
Sublevel
Parts of the periodic table corresponds to each
orbital shape (angular momentum number)
Groups 1 & 2 – s block
Groups 13-18 – p block
Groups 3-12 – d block
Bottom two rows – f block
Spin Quantum Number (ms)
• Indicates the spin of the electron
• Clockwise & Counter-clockwise
• A vertical arrow indicates an electron and its
direction of spin.
• In any orbital, the spin of the 2 electrons must
be opposite.
Principal Energy Levels
• # of orbitals in an energy level is equal to n2
• Max of 2 electrons can occupy a single orbital.
• The maximum number of electrons that can
occupy an energy level is 2n2
Quantum Numbers
The building = atom
Apartment Floors = Energy Levels (shells)
Specific Apartments = Orbitals (subshells)
Residents = Electrons