The periodic table of elements was invented and arranged by Russian chemist Dmitri Mendeleev in 1869. It arranges chemical elements into groups and periods. The elements are ordered by their atomic number, which is how many protons or electrons are in that particular element, and go from lowest to highest. Today, there are 118 known elements on the table.
Mendeleev was able to realize that he could arrange the 65 known elements on the table so that each element had a higher atomic weight than the atom on its left and similar properties as the elements in its column. By charting the elements like this, Mendeleev could see where there were gaps, meaning that there were more elements to discover.
Each row of elements across the table is a period. There are seven periods. Every row down the table is a group, of which there are eighteen. Elements in a group have their electrons arranged similarly, which makes the elements behave in similar ways. For example, group eighteen is called the Noble Gases because all of the elements in that group are gases that do not combine with any other atoms.
Chemists use the periodic table to observe patterns and relationships between the elements. An example of this is that elements on the top left of the table are the most metallic and elements on the bottom right of the periodic table are the least metallic. Another example is of the atomic radius. The atomic radius tends to decrease as one moves across the table to the right and the effective nuclear charge begins to increase. These are just two of many trends and patterns.
The periodic table of elements has played a crucial role in many scientific discoveries throughout history. It provides a simple and organized way to view all the known elements. Along with that, the table also shows many trends and relationships of elements. The periodic table is a vital part of science today, and will continue to be far into the future.