Tabla de Contenidos
Anyone who sees a modern periodic table will notice that it is almost always very colorful. Also, when comparing multiple tables with each other, you’ll also notice that even though the colors may be different, they always follow the same pattern. This is because the periodic table is color-coded, with those atoms that share physical or chemical properties with each other also sharing the same color. This color is different from the color of other atoms that exhibit different behavior.
In the following sections we will discuss why the elements in the periodic table are color coded and what is the importance of this coding. However, to give more context to this discussion, let’s start with a brief comment about the importance of the periodic table in chemistry and science in general.
Importance of the periodic table
The periodic table is one of the most important tools chemists have. It represents the culmination and summary of centuries of scientific research on the composition and properties of matter in general, and of the chemical elements in particular.
Since the Russian chemist Dmitri Mendeleyev proposed his model of the periodic table in 1869, it has been completed with the discovery or synthesis of new elements until, today, we have a table with 118 different elements ordered by their atomic number. in groups and periods .
The way elements are arranged on the periodic table allows us to reliably predict most of the physical and chemical properties of elements when compared to other members of their group. Many properties such as effective nuclear charge, common valences, atomic and ionic radius, ionization energy, and electron affinity vary predictably over a group or period. This information is extremely useful for predicting the type of chemical compounds that will form when one element combines with another, and even for predicting the type of chemical bond that will form between them.
Why is the periodic table color coded?
The amount of information that we possess today regarding each element is very large and it is impractical and even impossible to compress all this information in a small box of not much more than 1 cm 2 of area. This makes it necessary to find creative ways to encode the information, to allow the incorporation of more information in the same space. Using color codes is one of the simplest and most visually effective ways to achieve this.
How are the elements color coded on the periodic table?
There are different ways to color code the periodic table. Some are based on the physical properties and metallic character of the elements, others are based on the family or group of elements to which it belongs, while others are related to the values of some periodic properties such as electronegativity. Here are some of the more common ways to color code the periodic table.
Metallic character coding
The most common way to code the periodic table is based on the metallic character of the different elements. According to this criterion, the elements are broadly classified into metals, nonmetals, metalloids, and noble gases, but subdivisions can also be made within these large groups. The following table shows this subdivision highlighted through the use of different colors:
In this color coding, which, by the way, is the most common, we can notice 11 different colors. In this particular coding, the warmer colors are assigned to elements with a higher metallic character, while the cooler colors are assigned to those with a less metallic character, although this is not strictly necessary.
As seen in the legend, the orange group of elements corresponds to the alkali metals, the one to its right corresponds to the alkaline earths , and the elements in the center block are called transition metals or d-block elements (as indicated by the blue block in the small periodic table-shaped inset at the bottom left in the figure above).
The two separate rows of elements in the periodic table that have different shades of light green correspond to the internal transition metals (also known as rare earths or f-block elements, as indicated by the yellow block in the insert).
On the other hand, the deeper yellow elements to the right of the transition metals are the p-block metals. The deep green elements are elements that possess properties of both metals and nonmetals, which is why they are called metalloids or semimetals. The purple ones correspond to the nonmetals and the pink ones correspond to the halogens (which are also nonmetals, although they are identified separately in this table).
Finally, the group of blue elements corresponds to the noble gases and the gray elements are synthetic elements whose properties are unknown, so they cannot be classified in any of the other groups.
block encoding
Some periodic tables are coded in such a way that the color represents the block to which each element belongs, as shown in the following figure:
In this case, the code seeks to facilitate the recognition of the type of orbital or subshell in which the outermost valence electrons are found. In other words, it indicates the last sublevel (and therefore the secondary quantum number ) in which the last electrons that fill the electronic configuration of an element are located. There are only four sublevels in which the atoms in their ground state locate electrons, which are the s, p, d and f sublevels, which give rise to the four respective homonymous blocks.
Thus, the first two groups of the periodic table (alkali and alkaline earth metals) as well as hydrogen and helium, make up the s block of the periodic table (intense orange elements). Then, the yellow elements, which form groups 13 to 18 (not including helium), correspond to the p block (yellow block).
The central block elements correspond to the d block elements (which are filling do orbitals which easily form ions with partially filled d orbitals) and finally, the lanthanides and actinides (in green color) form the f block of the inner transition metals. , as mentioned earlier.
Coding by group or family of elements
Another relatively common way to code the elements is giving importance only to the group to which it belongs. These groups are often referred to as families of elements and are characterized by having the same or similar valence shell configurations. The following periodic table shows this coding, and the legend shows the name of each family, some of which have particular names, while in the case of the transition metals, the family is named after the first element of the respective group.
Electronegativity coding
In addition to the color groups mentioned above, some particular periodic tables use a color code adjusted to some scale that represents a physical or chemical periodic property. Such is the case of the periodic table of electronegativities that is presented below.
In cases like this, a specific color is usually assigned to each value of the property in question (in this case, electronegativity) or to each range of values. The colors can be arbitrary (as in the case of this image) or they can be assigned using some mathematical function of the property you are looking to encode.
For example, you can assign a single color and vary its hue based on the electronegativity value, so just by looking at the colors it is clear which elements have higher electronegativity and which have lower.
References
411 Answers. (nd). What is a color-coded periodic table? 411ANSWERS.COM. https://en.411answers.com/a/what-is-a-color-coded-periodic-table.html
Chang, R. (2012). Chemistry (11th ed .). McGraw-Hill Education.
Org Elements (2022, March 13). Periodic Table of the Elements . https://elementos.org.es/tabla-periodica
Hernández, L. (2012, August 25). Beware of the colors of the periodic table. Science Online. https://www.cienciaonline.com/2012/08/25/cuidado-con-los-colores-de-la-tabla-periodica/
Les Kanaris. (nd). Why is the periodic table color coded? https://us.leskanaris.com/2735-what-is-the-importance-of-color-on-the-periodic-tabl.html
Little.Is. (2021, July 14). Colors of the periodic table of the elements . Proco.es. https://proco.es/arte-y-diseno/colores-de-la-tabla-periodica-de-los-elementos/
