The concept we are looking for here is electronegativity. This concept is a measure of how strong an atom or element can attract a pair, that is bonding, of electrons to itself.
Fluorine is the element or atom of the greatest electronegativity. Electronegativity would increase as we move left to right of the periodic table.
Ligands are small molecules that transmit signals in between or within cells. Ligands exert their effects by binding to cellular proteins called receptors.
