Most explosives are not elements, they are compounds, however several elements will react explosively under some conditions.
Caesium (132 amu) reacts explosively with water, as would Francium (but Francium is so rare that no one has isolated enough to see or weigh)
Several heavy radioactive substances can be made to undergo fission, especially plutonium-239)
The heaviest element in the periodic table (known in March 2013) is ununoctium.
The information in the question 'What is the heaviest element?' should answer this. Access this by the web link below.
Einsteinium is a radioactive element and is not inherently explosive. However, it can release energy in the form of radiation as it decays, but it is not known to exhibit explosive properties.
Now californium is considered as the heaviest naturally occurring chemical element.
Mercury is the heaviest element at a liquid state.
The heaviest (hevest?) naturally occurring element is Uranium (238 a.m.u.) but the heaviest known element is atom number 114, 117 or 118, the exact mass being unknown but over 250.
The heaviest element that is highly radioactive is Ununoctium, which has an atomic number of 118.
The heaviest stable element is bismuth, atomic number 83, atomic weight 208.9804). Any heavier element is radioactive, which means it decays into lighter elements - uranium, the heaviest naturally occurring element, will eventually decay into lead-207.
The heaviest element announced in February 2004 was ununpentium with the atomic number 115.
Granite.
The heaviest element with a one letter atomic symbol is uranium (symbol: U).
This element is francium.