ATOMIC STRUCTURE ANALOGIES
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The immensity of Avogadro's Number (AN) is so great that it is
impossible for a person to have a true realization or comprehension of
just how large it is. As a result, analogies are used to try to get some
idea of its size.
This group of analogies are examples of typical textbook analogies:
a) AN of marbles spread over the surface of the earth, would produce a
layer of marbles about 50 miles thick.
b) AN of grains of sand spread over the United States, would produce a
layer of sand about 3 inches deep.
c) It would take 3 million years for the world's entire population of
6.5 billion people, counting at the rate of one object per second, to
collectively count an Avogadro's Number of objects
Poskozim,J. Analogies for Avogadro's Number Journal of Chemical
Education 1986, 63(2), p.125
As you go down a vertical group in the periodic table, the trend is
that the atomic radius increases as more energy levels are added on. This
is similar to the observation that as a tree adds on growth rings, the
stem becomes larger in radius.
The increasing atomic size as you go down a vertical group or family in
the periodic table is similar to the pattern of increasing size shown by
the spots on a giraffe's neck as you go from its head down to the body.
Parking lot rows are analogous to the energy levels in an atom in the
Different numbers of electrons are found in different energy levels.
Similarly, not all rows will hold the same number of cars, depending on
the location and shape of the rows.
The energy levels, generally speaking, fill from the nucleus outwards.
Similarly, the arena in which the basketball or hockey game is being
played, represents the nucleus of the atom. The parking lot rows that are
closest to the arena are always the ones which get filled up first, and
the farther away ones later.
The ionization energy of an electron in an outside energy level is
smaller than for an electron in an inner level. Similarly, a car parked on
an outer row of the parking lot can generally get out of the lot easier
after the event, than a car located in one of the congested inner rows,
closer to the arena (nucleus).
One of the main postulates of the Bohr Model of the atom is that
electrons can only exist in certain stable energy levels. It is analogous
to saying that when you stand on a ladder you have a certain amount of
potential energy at each rung position, and you can not stand at any in
betwen position or have any in between amount of energy. If you do try to
stand at a position in between two rungs, you will always automatically
slide down to a lower rung and a correspondingly lower energy position.
According to the Bohr Model, electrons can only exist in particular
energy levels around the nucleus. This is like a stick shift on an
automobile ... it only works when it is in 1st gear, 2nd gear, etc ... and
not at any in between position.
Hund's Rule states that in order for electrons to be in a state of
lowest energy, no electron pairing takes place until each orbital in the
sublevel contains one electron.
If the empty seats on a bus represent the available orbitals in a
given sublevel, one would normally observe that strangers would tend to
sit in separate seats until all the seats contain one person, then begin
A stranger who came and sat on your seat even though other empty seats
were available, might put you into an anxious or "excited" state since you
would be wishing the person would move to an unoccupied seat.
Source: Goh, Ngoh Khang; Chia, Lian Sai; and Tan, Daniel.
Some Analogies for Teaching Atomic Structure at the High School Level Journal
of Chemical Education September 1994, 71(9), p.733
When a beam of low frequency, low energy light is directed onto a metal
surface, it will reflect off with no effect upon the metal. If many light
sources of the same frequency are used, there is still no effect on the
metal. An analogy would be that if you shoot at a person in a suit of
armor using either a single BB gun or many BB guns at once, the person
inside the armor will not be affected.
If light of higher frequency and energy from only a single source is
used, then this greater amount of energy may be absorbed and cause
electrons to be promoted and ejected. Similarly, if the BB gun is replaced
by a more powerful rifle, then it would only take one shot to pierce the
armor and hurt the person inside.
Source: McCullough, Thomas Simple Analogies in General
Chemistry Journal of Chemical Education July 1992, 69(7), 543.
According to the Quantum Theory, an electromagnetic wave guides a flow
of energy which is transported along the wave in bundles (photons) of size
hf. A simplified view of the situation would be to say that if a wave was
represented by a group of people marching in a line, the photons would be
analogous to the backpack each person was wearing, and each of which
contained a particular amount of material. This analogy could be extended
to say that older, more energetic adults would carry a greater load in
their backpacks than would children.
When a power boat is cruising on a lake, the wave which it produces has
its greatest amplitude right at the boat, and the amplitude decreases as
the distance from the boat increases. Thus you could locate the most
probable location of the boat by analyzing the amplitude and energy of its
associated water wave.
This is analogous to the wave mechanical model which visualizes the
atom as a positive nucleus surrounded by vibrating electron waves. The
Schroedinger Wave Equation describes the amplitude and other
characteristocs of the waves which are associated with the moving
electrons, and thus it also is able to describe the energy and location of
the orbiting electrons.
Sometimes electrons are described as being small particles of matter.
At other times when we describe the organization and behavior of
electrons, we treat them as wave patterns.
Someone who had never seen a television would report seeing
recognizable images of people, buildings, etc. when watching the screen
from across the room. However, a similar observer, if placed with their
eye right up against the screen, would report seeing dots of varying
colors and brightness. Both descriptions of the screen are correct; the
perspective of the viewer determines which properties are observed at that
Source: Licata, Kenneth P. Chemistry Is Like a ... Science
Teacher 1988, 55(8), p.42
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