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Melting Point and Atomic Radius
Name: Michael
Status: student
Grade: 9-12
Location: MN
Country: United Kingdom
Date: Winter 2009-2010
Question:
What is the relationship between melting point and
atomic radius?
Replies:
Hi Michael,
There appears to be no particular connection between atomic radius of an
element and its melting point. Lithium, tellurium, palladium and iodine, for
example, have nearly identical atomic radii (145 picometers, 140 pm, 140
pm and 140 pm respectively) yet their melting points are (respectively)
180°C, 450°C, 1555°C, and 114°C.
Another example is to compare cobalt, iridium, and tungsten. All three have
an atomic radius of 135 pm, but their melting points are 1495°C, 2466°C and
3422°C respectively. An extreme example is to compare zirconium (155 pm
radius) and mercury (150 pm radius). Although their atomic radii are nearly
identical, the melting points are not even close. Zirconium's melting point is
1855°C, but mercury is already a liquid at room temperature (its melting
point is -40°C!!).
What can be said is that in any ONE row in the periodic table, atomic radius
tends to grow smaller as you move to the right, and melting point tends to
decrease. Similarly, in any ONE column (e.g. the alklai metals), moving
downwards tends to result in increasing atomic radius, and increasing
melting point.
Hope this helps.
Regards,
Bob Wilson
Michael
I do not know that there is a relationship between melting point and atomic
radius.
This definition of "melting point" is from:
http://en.wikipedia.org/wiki/Melting_point
The melting point of a solid is the temperature at which the vapor pressure
of the solid and the liquid are equal. At the melting point the solid and
liquid phase exist in equilibrium. When considered as the temperature of the
reverse change from liquid to solid, it is referred to as the freezing
point. Because of the ability of some substances to supercool, the freezing
point is not considered to be a characteristic property of a substance. When
the "characteristic freezing point" of a substance is determined, in fact
the actual methodology is almost always "the principle of observing the
disappearance rather than the formation of ice", i.e. the melting point.[1]
Here is a table of the melting points of most of the elements:
http://en.wikipedia.org/wiki/List_of_elements_by_melting_point
Sorted by their melting points. You can click on the little arrows at the
top of each column to sort them by that category.
If they are ordered by melting point, you can refer to their atomic weight
headed by the column with a "Z" in it. In ascending order of melting
points, the atomic weights appear to be in random order.
Cheers,
Mike Stewart
Relating melting point and atomic radius is not a connection that is
"profitable". There are too many factors that influence the melting point.
In addition, atomic radius depends upon whose model used.
While there are some gross trends, I believe the simplest answer is "no".
Vince
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Update: June 2012
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