Download Chapter 13 Notes - Net Start Class

Chapter 13 Notes
Electron Models
Evolution of Electron Models
• The first model of the electron was given
by J.J. Thompson—the electron’s
discoverer. His was the “plum pudding”
model.
The Rutherford Model
• With Rutherford’s discovery of the
nucleus of an atom, the atomic model
changed.
The Bohr Model
• Niels Bohr introduced his model, which
answered why electrons do not fall into the
nucleus.
• He introduced the concept of energy levels,
where the electrons orbited similar to the
way the planets orbit the sun.
Bohr Model and Energy Levels
• In the Bohr model, electrons are in energy
levels, or regions where they most probably
are orbiting around the nucleus.
• The analogy is that energy levels are like
the rungs of a ladder—you cannot be
between rungs, just like an electron
cannot be between energy levels.
• A quantum of energy is the amount of
energy it takes to move from one energy
level to the next.
Quantum Mechanical Model
• In 1926, Erwin Schrodinger used the new
quantum theory to write and solve
mathematical equations to describe electron
location.
The Quantum Mechanical Model, cont.
• Today’s model comes from the solutions to
Schrodinger’s equations.
• Previous models were based on physical
models of the motion of large objects.
• This model does not predict the path of
electrons, but estimates the probability of
finding an electron in a certain position.
• There is no physical analogy for this model!
Where are the electrons?
• In an atom, principal energy levels (n) can
hold electrons. These principal energy levels
are assigned values in order of increasing
energy (n=1,2,3,4...).
• Within each principal energy level, electrons
occupy energy sublevels. There are as many
sublevels as the number of the energy level
(i.e., level 1 has 1 sublevel, level 2 has 2
sublevels, etc.)
Where are the electrons?
• There are four types of sublevels we will talk
about—s,p,d and f. Inside the sublevel are
atomic orbitals that hold the electrons. Every
atomic orbital can hold two electrons.
• S has one orbital, P has three, D has five and
F has seven. How many electrons can each
one hold?
Orbital Shapes
s orbital = s sublevel
+
px orbital
+
py orbital
= p sublevel
pz orbital
Where are the electrons?
• So how many electrons can each energy level
hold?
– Level 1 has an s sublevel=2 e– Level 2 has an s and a p sublevel=8e– Level 3 has an s, p and d sublevel=18e– Level 4 has an s, p, d and f sublevel=32e-
Electron Configuration
Electron Configuration
• In the atom, electrons and the
nucleus interact to make the
most stable arrangement
possible.
• The ways that electrons are
arranged around the nucleus
of an atom is called the
electron configuration.
Aufbau Principal
• Electrons enter orbitals of the lowest energy
first.
Pauli’s Exclusion Principal
• An atomic orbital may describe at most two
electrons.
Hund’s Rule
• When electrons occupy orbitals of equal
energy, one electron enters each orbital until
all orbitals contain one electron with parallel
spins.
EMR and
Quantum Theory
How did scientist find out about
energy levels and sublevels?
• When we previously found the
electron configuration for elements, it
was for electrons at ground state (the
lowest energy possible).
How did scientist find out about
energy levels and sublevels?
• As energy is added to atoms, they
absorb the energy by electrons going
from ground state to an excited state,
where electrons are no longer in the
lowest energy orbitals.
How did scientist find out about
energy levels and sublevels?
• Electrons can then only go back to
ground state by releasing the energy,
usually in the form of light in discreet
packets called photons.
How did scientist find out about
energy levels and sublevels?
• If electrons could orbit anywhere,
when they went from excited state to
ground state they would emit light of
all wavelengths.
• This doesn’t happen! Only certain
wavelengths of light are emitted,
which is different for each atom.
How did scientist find out about
energy levels and sublevels?
• This is called an atomic emission
spectra, and is different for every
element!
How did scientist find out about
energy levels and sublevels?
• A scientist named Max Planck studied
the cooling of metal and how its color
changes, and tied the idea of
frequency of light to energy.
• The bands of light correspond to the
specific energy levels.