Semiconductor nanoparticles (also called quantum dots or nanocrystals) are generally used a lasing medium in a laser, as fluorescent tags in biological testing methods, and as electronics devices. However, these nanoparticles traditionally have high production costs and the methods used for synthesis are extremely toxic at high temperatures, posing safety risks during mass production. Additionally, it has been difficult to form nanoparticles of uniform size. This invention is directed to semiconductor nanoparticles having an elementally passivated surface. These nanoparticles are capable of being suspended in water without substantial agglomeration and substantial precipitation on container surfaces for at least 30 days. The method of making the semiconductor nanoparticles includes reacting at least a first reactant and a second reactant in a solution to form the semiconductor nanoparticles in the solution. A first reactant provides a passivating element which binds to dangling bonds on a surface of the nanoparticles to passivate the surface of the nanoparticles. The nanoparticle size can be tuned by etching the nanoparticles located in the solution to a desired size. Additionally, nanoparticles of this technology with a passivated surface decreases bonding between nanoparticles and thus decreases nanoparticle agglomeration. A passivated surface comprises surface having passivated dangling bonds, where a passivating element is bound to the dangling bonds. Furthermore, the passivating element reduces or eliminates undesirable reconstructions of atomic positions on the nanoparticle surface which cause energy levels to appear within the band gap of the nanocrystals. These extra energy levels may lead to decreased light emission at desired wavelengths and emission and absorption of light at undesired wavelengths.