Chemical element of metals. Cu comes from Cuprum, Fe comes from Ferrum, Ag from Argentum. The symbols were not followed by a period (full stop) as with abbreviations. Later chemical elements were also assigned unique chemical symbols, based on the name of the element, but not necessarily in English. For example, sodium has the chemical symbol 'Na' after the Latin "natrium". The same applies to "W" (wolfram) for tungsten, "Fe" (ferrum) for iron, "Hg" (hydrargyrum) for mercury, "Sn" (stannum) for tin, "K" (kalium) for potassium, "Au" (aurum) for gold, "Ag" (argentum) for silver, "Pb" (plumbum) for lead, "Cu" (cuprum) for copper, and
Melting point the same space. The Lindemann criterion states that melting is expected when the vibration root mean square amplitude exceeds a threshold value. Assuming that all atoms in a crystal vibrate with the same frequency "ν", the average thermal energy can be estimated using the equipartition theorem as where "m" is the atomic mass, "ν" is the frequency, "u" is the average vibration amplitude, "k" is the Boltzmann constant, and "T" is the absolute temperature. If the threshold value of "u" is "ca" where "c" is the Lindemann constant and "a" is the atomic spacing, then the melting point is estimated