What is a chelate?

Ferrous (II) Sulfate Heptahydrate

Edta Molecule

Chelates are organic molecules that can trap or encapsulate certain highly reactive trace metal cations which prevent them from entering into unwanted chemical reactions and forming insoluble compounds, which are unavailable.
Chelates incorporate metal ions into a soluble but bound form, to make them available to the plant because they are very soluble in water.
Chelation is bonding the metal ion to an organic molecule, making the metal ion highly soluble.
A chelated form of a mineral has different qualities from the mineral itself. 
One quality that can change is bioavailability; the ability to absorb and use the mineral.
Bioavailability can be increased or decreased depending on the mineral-chelate complex formed.
Some synthetic metal-chelate complexes form extremely strong bonds and bind minerals so tightly that they are unavailable for their physiological functions, and if used in foliar fertiliser has a great deal of trouble releasing the metal ion once in the plant.
Metal-chelate complexes used in foliar fertilisers need to form bonds strong enough to protect them from unwanted chemical reactions but once in the plant should release easily.
Natural chelating agents do not share the problems of the synthetics and are state-of-the-art technology for delivering selected mineral and trace elements with maximum bioavailability, tolerability and safety
If a yield-limiting deficit is suspected or established then the chelated mineral applied as a foliar will address that deficit more accurately and with greater speed than any other nutrient.
These elements are far more easily absorbed by plant roots and leaves in this chelated form because of changes in the electrical charge from the trace minerals as a result of their organic encapsulation.
The chelation process removes the positive charge from the metals, allowing the neutral or slightly negatively charged, chelated molecule to slide through the pores on the leaf and root surface more rapidly.
These pores are negatively charged, so there is a problem with fixation of positively charged minerals at the pore entrance.

There is no such restrictive barrier for the neutral, chelated mineral.