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Chapter 4
Electronic Structure
of Atoms
Electronic
Structure
of Atoms
Waves
• The distance between corresponding points
on adjacent waves is the wavelength ().
Electronic
Structure
of Atoms
Waves
• The number of waves
passing a given point per
unit of time is the
frequency.
• For waves traveling at
the same velocity, the
longer the wavelength,
the smaller the
frequency.
Electronic
Structure
of Atoms
Electromagnetic Radiation
• All electromagnetic
radiation travels at the
same velocity: the
speed of light (c), 3.00
x 108 m/s.
• Only Frequency and
Wavelength change.
Electronic
Structure
of Atoms
The Nature of Energy
• The wave nature of light
does not explain how
an object can glow
when its temperature
increases.
• Max Planck explained it
by assuming that
energy comes in
packets called quanta.
Electronic
Structure
of Atoms
Quantum
• A quantum of energy is the minimum
quantity of energy that can be lost or
gained by an atom.
• Planck suggested that objects emit
energy in small packets called quanta.
Electronic
Structure
of Atoms
The Nature of Energy
• A photon is a particle of
electromagnetic radiation
having zero mass and
carrying a quantum of energy
Electronic
Structure
of Atoms
The Nature of Energy
Another mystery
involved the
emission spectra
observed from
energy emitted by
atoms and
molecules.
Electronic
Structure
of Atoms
Emission Spectrum
• The lowest energy state of an atom is its
ground state.
• A state in which an atom has a higher potential
energy than it has in its ground state is an
excited state.
• When a narrow beam of light is shined through
a prism, it is separated into 4 specific colors.
The 4 bands are known as hydrogen’s lineemission spectrum.
Electronic
Structure
of Atoms
Emission Spectrum
• When 1st experimented with, scientists
expected to get a continuous range of
frequencies of electromagnetic radiation and
not 4 frequencies. This was known as a
continuous spectrum.
• Disproving the continuous spectrum led to an
entirely new atomic theory known as quantum
theory.
Electronic
Structure
of Atoms
Quantum Theory
• Whenever an excited atom falls to its ground
state or to a lower-energy excited state, it emits
a photon of radiation.
• Excited neon atoms emit light when electrons in
higher energy levels fall back to the ground
state or lower levels. This is what produces the
neon glow.
Electronic
Structure
of Atoms
The Nature of Energy
• Niels Bohr adopted
Planck’s assumption and
explained these
phenomena in this way:
1. Electrons in an atom
can only occupy
certain orbits
(corresponding to
certain energies).
Electronic
Structure
of Atoms
The Nature of Energy
2. Electrons in
permitted orbits
have specific,
“allowed” energies;
these energies will
not be radiated
from the atom.
Electronic
Structure
of Atoms
The Nature of Energy
3. Energy is only
absorbed or emitted in
such a way as to move
an electron from one
“allowed” energy state
to another.
Electronic
Structure
of Atoms
Quantum Numbers
• Electrons do not travel around the nucleus in
neat orbits as Bohr thought but instead in
certain regions called orbitals.
• An orbital is a 3-dimensional region around the
nucleus that indicates the probable location of
an electron.
• Orbitals have different shapes and sizes.
Electronic
Structure
of Atoms
Value of l
0
1
2
3
Type of orbital
s
p
d
f
Electronic
Structure
of Atoms
•
•
•
•
•
•
•
•
•
•
1s = 2 electrons
2s = 2 electrons
2p = 6 electrons
3s = 2 electrons
3p = 6 electrons
3d = 10 electrons
4s = 2 electrons
4p = 6 electrons
4d = 10 electrons
4f = 14 electrons
Electronic
Structure
of Atoms
Hund’s Rule
Electronic
Structure
of Atoms
Orbital Diagrams
• Each box represents
one orbital.
• Half-arrows represent
the electrons.
• The direction of the
arrow represents the
spin of the electron.
Electronic
Structure
of Atoms
Electronic
Structure
of Atoms
Lithium – atomic number 11
Draw the orbital notation
Electronic
Structure
of Atoms
Boron’s electron configuration
Atomic number = 5
Electronic
Structure
of Atoms
The electron configuration of boron is 1s22s22p1.
How many electrons are present in an atom of
boron? What is the atomic number for boron?
Write the orbital notation for boron.
• The number of electrons is equal to the sum of
the superscripts = ______
• The number of protons = electrons so the
atomic number = _____
Electronic
Structure
of Atoms
Write both the complete electron
configuration for iron, Fe.
Electronic
Structure
of Atoms