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Analogies for Avogadro's Number

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
Source: Poskozim,P.;Wazorick,J.;Tiempetpaisal,P.;and Poskozim,J. Analogies for Avogadro's Number Journal of Chemical Education 1986, 63(2), p.125
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Atomic Size is like the Growth Rings of a Tree

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.
Source: Original
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Atomic Size is like the Spots on a Giraffe's Neck

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.
Source: Original
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Energy Levels are like Rows in a Parking Lot

Parking lot rows are analogous to the energy levels in an atom in the following ways:
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).
Source: Original
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Energy Levels are like Standing on a Ladder

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.
Source: Original
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Energy Levels are like a Stick Shift

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.
Source: Unknown
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Hunds Rule and Excited State is like Strangers Getting on a Bus

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 pairing up.
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
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Photoelectric Effect is like Shooting with Different Guns

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.
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Photons are like Backpacks

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.
Source: Original
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Wave Mechanical Model is like a Power Boat

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.
Source: Original
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Wave Particle Duality is like Watching a TV Screen

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 moment.
Source: Licata, Kenneth P. Chemistry Is Like a ... Science Teacher 1988, 55(8), p.42
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From this Analogies page you can go either to the other analogy pages:
[ Atomic Structure | Biology | Chemical Bonding | Chemical Reactions]
[Electrolytes | Equilibrium | Matter ]

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