Transcript Chapter 7: Completing the Model of the Atom

Chapter 7:
Completing the
Model of the
Atom
Section 7.1: Expanding the
Theory of the Atom
Electrons
 Occupy
 electron
a complex world of energy levels
distribution in energy levels of an
atom account for many of the physical
and chemical properties of the element
Energy levels
Electrons with the most energy are farthest
from the nucleus and occupy the
outermost level
Review of Electromagnetic
Radiation and Energy levels
 Waves
have a range of freq. and
wavelengths


Higher freq = Shorter wavelength = Greater
energy
Lower freq = Longer wavelength = Lower
energy
Review of Electromagnetic
Radiation and Energy levels
(cont)
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Use to calculate the exact amount of energy released by electrons
in atoms
•
By absorbing a specific amount of energy, an e- can jump to a
higher energy level
•
When an e- falls back to a lower energy level, it releases the same
amount of energy in the form of radiation (light) with a definite
frequency
•
The energy (color) of light depends on how far the electron falls
•
Greater energy = Color more toward the violet end of spectrum
Heisenberg’s Uncertainty
Principle
 States
that it is impossible to measure
exactly both the position and momentum
(mass and speed) of an object (electron)
 This
led to the electron cloud model in
atoms
Electron cloud model
Because we cannot pinpoint exactly
where an electron is on the “surface” of
an atom, we refer to its position as an
electron cloud.
The chemical behavior and properties of
any 2-subtances are determined by the
number of these electrons around the
nucleus
How do we describe the
electron cloud?
 We
use quantum numbers. These
represent the energy states of the
electron.
 These
difference in energy states were
“discovered” due to the different spectral
lines of an emission spectrum.
Quantum Numbers
There are 4 quantum numbers that describe
the electron distribution of electrons in an
atom
They are n, l, m and s
Principal quantum number, n
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Describes the general size of the electron cloud
Numbered levels low to high – 1,2,3,4…(integers)
Electrons may be found in each
The maximum # of electron possible in any one
level is 2n2
We have been calling these energy levels, 1-7
Each main energy level has sublevels
Angular quantum number, l
 Describes
the shape of the electron cloud
 It represents the sublevels within an
energy level
 The value of l is 0 to (n-1)
 The number of sublevels is equal to the
value of n
 The lowest sublevel is s, then p, d and f
Angular quantum number, l
(cont)
 Each
sublevel can hold up to a specific #
of electrons:




s sublevel can hold 1 pair (2 electrons)
p can hold 3 pair (6 electrons)
d can hold 5 pair (10 electrons)
f can hold 7 pair (14 electrons)
 Each
pair has a different place in space,
this space is called an orbital.
Orbitals
Angular quantum number, l
(cont)
 The
sum of all the electron clouds in any
sublevel is a spherical cloud.
 Electrons are repelled by each other and
attracted to the positive nucleus
Blocks in the Periodic Table
Magnetic Quantum Number,
m
 Describes
the orientation in space of a
particular orbital
 The value is any integer between +l and -l
Electron Spin Quantum
Number, s
 Describes
the spin of the electron within
an orbital
 The value is +1/2 (clockwise) or -1/2
(counterclockwise)
 If there are 2 electrons in an orbital, they
must spin in opposite directions.
Hund’s Rule
In a set of orbitals, the electrons will fill the orbitals in a
way that would give the maximum number of parallel
spins (maximum number of unpaired electrons).
Analogy: Students could fill each seat of a school bus,
one person at a time, before doubling up.
Orbital
Diagram for
Hydrogen
Orbital
Diagram
for Helium
Orbital
Diagram
for Lithium
Orbital
Diagram
for
Beryllium
Orbital
Diagram
for Carbon
Orbital
Diagram
for Nitrogen
Standard Notation
of Fluorine
2
1s
Number of electrons
in the sub level 2,2,5
2
2s
5
2p
Sublevels