in StemSocial10 months ago

Author: @madridbg, through Power Point 2010, using public domain images. andreas160578

Greetings and welcome dear readers of the #Hive platform who are passionate about scientific content with practical contributions from a flexible perspective. In this sense, through the publication that we will share through the @Stemsocial community, we seek to address the chemical processes behind the process of photocopying or xerographic techniques, as a technological advance with great importance in the business and academic world.


It is no secret that chemistry is based on the understanding of the periodic properties of the different elements that make up the periodic table and that are present in our lives, either naturally or synthesized by the hand of man.

In this sense, and with the intention of achieving a conceptual approach according to the title of this thematic we will analyze some basic characteristics that manifest the elements belonging to group 6A, among which stand out Sulfur, Selenium, Oxygen, Polonium and Tellurium.

These elements are great representatives of chemical behavior, for example the oxygen present in all combustion processes and is essential for life on the planet, sulfur, substances necessary in amino acids and photovoltaic process among other applications and uses that we can give these substances.

However, in this research we will focus on the use of selenium mainly of non-metallic character, a lustrous semiconductor applied in the processes of copying and reproduction of images on paper, fundamentals that we will describe below.


In this section we will focus on a specific periodic property, which refers to the electronic configuration of the elements of group 6A, which in general have a s2p4 configuration, according to the rain method, which implies that in its last valence layer only two electrons are missing to generate a complete octet.

This quality is responsible for oxygen being highly oxidizing, a property that is affected as the metallic character intensifies, so it is to be expected that the last two members of this group (selenium and tellurium) present greater metallic characteristics and behave as reducing agents, a fact attributable to the loss of electronegativity of these elements.

Fig. 2. Periodic table of the chemical elements. Author: Attribution: 2012rc

In the case of selenium, it can be found in various allotropic forms, starting with liquid selenium, which can melt at over 180 degrees Celsius, is insoluble in water and alcohol and partially soluble in carbon disulfide and is highly soluble in ether. Among the fundamental characteristics of the element in terms of this writing, highlights the ability to convert light into electricity through the photoelectric effect phenomenon that we will describe in the next section.


Prints on paper have been of growing interest for human development, which is why different methods have been implemented that allow us to obtain better quality and durable images over time.

Among the methods implemented, wet photographic methods and printing using carbon paper stand out. However, these advances seem to have become obsolete from 1950, where technological processes began to emerge in terms of images and today we can reproduce images of unimaginable qualities.

Fig. 3. Representation of photocopying machine, by means of selenium drum Author: pxfuel

But beyond the advances generated, the appearance of the photocopying process revolutionized business and office work, thanks to the diversification, speed and efficiency of these amazing machines.

Nowadays, wet compiling has been replaced by dry processes (xerography) where the photoconductive properties of selenium are used. This process implies that the conductivity of this element increases by a factor of 1000 when it is exposed to light and when light decreases, conductivity decreases.

Fig. 4. Representation of the xerographic process Author: Yzmo

Chemically the process starts when the drum filled with selenium is uniformly charged with positive charge, which when exposed to a lens irradiated with light, is able to generate an image according to the electrical charges, which is transferred to the paper when the element in the drum loses conductivity due to the absence of illumination.

At this point, it is necessary for the paper to come into contact with the negatively charged toner which will be responsible for printing the image that we can perceive sensorially through our eyes. So the toner particles act as a pigment that when heated adheres to the paper fixing the image and restarting the process for a new copying action.


Undoubtedly, chemical processes are indispensable in our daily work, from those related to metabolic issues, to major technological advances that have chemical systems as the main engine of operation.

Hence the need to keep us informed and with basic knowledge that allows us to generate a holistic view of reality and scientific knowledge. That is why through this topic we have been able to make a conceptual approach to issues related to the periodic properties and the photoelectric effect exhibited by the elements.


[1] Chang, R. (2010). Química. Decima edición. McGraw-hill Interamericana editores. ISBN: 978-607-15-0307-7.

[2] Ralph, H. Petrucci, William S. Harwood, E. Geoffrey Herring. (2003). QUIMICA GENERAL. Octava edición. PEARSON EDUCACIÓN. S.A., Madrid.



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I never knew the drum is usually filled with selenium. When a drum becomes bad, does it means that the selenium has been exhausted and if otherwise, does the selenium gets to pollute the environment?

Greetings friend @gentleshaid, first of all thank you for stopping by and expressing your concerns.

In this regard, we should be clear that:

"Chemically the process begins when the drum filled with selenium is uniformly charged with positive charge, which when exposed to a lens irradiated with light, is able to generate an image according to the electrical charges, which is transferred to the paper when the element in the drum loses conductivity due to the absence of illumination."

If we start from the above we realize that selenium is not depleted in this process, because it enters into a cycle or a kind of restoration based on illumination, so that the material that is depleted is the charged pigment in the barrel and that is negatively charged in order to interact with selenium through the luminous phase.

So if we analyze these fundamentals according to the pollution of the environment, the plastic waste in the barrel ends up accumulating and generating sources of pollution.

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