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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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