The periodic table is universally recognized in chemistry for organizing all known chemical elements. It has widespread use in chemical engineering, physics, biology and other hard sciences. Despite its common use, it can be quite confusing upon first glance. However, after the major parts are explained, the table’s value and uses become more obvious.
The first thing you notice when looking at the table are the obvious letters and numbers. The letters are the abbreviations for each represented element. Some are obvious, like O for oxygen and N for nitrogen, while others aren’t nearly so simple, like Fe for iron or K for potassium. The numbers are the atomic numbers, or number of protons in the nucleus (and number of electrons if the element is chemically neutral). The table is ordered by this atomic number and allows for the periodic trends explained below.
The table was first created in the mid 1800s with a “periodic” pattern. This pattern exists because elements had repeating characteristics that made them easy to classify. This system of patterns was first noted after the discovery of valency, or the common reactivity patterns of elements. For instance, carbon generally reacts with elements in groups of four because of the 4 valence electrons available for binding. This recurring patterns have led to the table being developed with three major classifcations: periods, groups and blocks.
The first category is known as a group. Also known as families, groups are the vertical columns of the table and present the easiest classification system in the table. The elements in a group have very similar properties, despite different atomic numbers and other atomic properties. For instance, group 18 is known as the noble gases. They are found in the 18th, or last, column of the table. They all display little reactivity with other elements and have the same basic properties: odorless, colorless gases.
Next are blocks, which are the separated regions of the table that have similar general properties defined by their electron configuration. For instance, groups 3 through 12 represent what are known as the transition elements. They are all metals with some level of reactivity to other elements. This categorization allows broader classifications within the table that take advantage of larger periodic trends.
Lastly are the periods, which are horizontal rows in the table. While they don’t generally have similarities, they represent repeating electron conditions. For instance, as you move across each period you can see trends that include changes in atomic radius, electronegativity, and ionization energy. While they aren’t strictly increasing the whole way across, the pattern in each row appears to repeat from row to row.