The periodic table is a device for organizing and categorizing all of the known chemical elements. Its setup is fairly straightforward, despite seeming confusing and overwhelming upon first inspection. However, after the major trends in the table are explained, it becomes a very useful tool for understanding basic chemistry.
The table was first created by Dimitri Mendeleev in the mid 1800s with a “periodic” pattern. This pattern exists because elements had repeating characteristics that made them easy to classify. This recurring patterns have led to the table being developed with three major classifcations: periods, groups and blocks.
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.
Blocks are the separated regions of the table that have similar general properties. 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.
Periods 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 increasing 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.
General Breakdown of the Table
As mentioned before, groups 3 through 12 are the transition metals or the d-block. Group 1 is known as the alkali metals, which are all highly reactive and never found pure in nature, and group 2 is the alkaline earth metals, which are very reactive with oxygen and are often found in fairly high concentrations in the earth. These two groups represent the s-block. Groups 13 to 18 represent the semimetals and has the noble gases, as well as more reactive halogens, and is known as the p-block.
The f-block, which is separated from the rest of the table, has high atomic element numbers split into two periods: the lathanides and actinides. These two periods show more similarity within the period than the elements do in the traditional groups categories, an exception to the trend found consistently throughout the rest of the table.