# How the Periodic Table of the Elements is used in Chemistry

The periodic table of the elements is a visual representation of all 118 chemical elements. For the uninitiated it often appears to be an useless jumble of undecipherable numbers, letters, and symbols. However, for those who have learned to understand it, it is an invaluable tool. Professional chemists and beginning chemistry students alike rely on it daily as a reference for the structures and properties of all the chemical elements. Its usefulness stems from a few main characteristics of its design.

First is the way it is arranged. Russian chemistry teacher Dmitri Mendeleev developed the table so that each row (called a period) follows periodic trends in the elements. As you go across the table you are able to observe some specific trends in the structure and properties of atoms. For example if a chemist wants to quickly reference the chemical reactivity of an element he simply has to glance at the table. He will automatically know that elements to the far left and far right of the table (excluding the final group which are nonreactive) will be more likely to react then those in the middle. The same is true for elements near the bottom of the table compared to those near the top. Some other notable trends that can be easily displayed and referenced by looking at the periodic table are as follows:

1. Atomic radii increases from right to left and from top to bottom on the table.

2. Ionization Energy (the amount of energy required to remove an electron from an element) increases from left to right and top to bottom across the table.

3. Ionic Size decreases from top to bottom.

First year chemistry students are taught these trends and can then use the table as a quick reference sheet to compare elements for these properties.

Another major use of the table is as a reference to determine atomic structure. The table is arranged by atomic number which corresponds to the number of protons, and consequently the number of electrons, in an atom. When you couple this knowledge with the mass number displayed on most tables (protons+neutrons) you can subtract the atomic number from the mass number to find the number of neutrons the element has. This information allows you to know and draw the structure of any atom.

The knowledge of the number of electrons is enough to determine how the elements will bond. Most high school chemistry students will have the knowledge to draw electron dot structures, and eventually Lewis structures for compounds, using only their periodic table as a guide.

Yet another use of the table is as a reference for the identifying properties of the elements. If you were trying to determine which element a substance was you could do so with basic properties like its state of matter, melting point, boiling point, and chemical reactivity. Some more advanced periodic tables will have all of this information and more. Knowing this information you will be able to identify most elements, and even determine their general uses.

Whether a beginner who relies on the table for all of their basic chemistry knowledge, or a professional using it as a quick and reference sheet, the period table plays a major role in the work of all chemists. It saves countless hours of looking up properties of elements. It is also a visual tool that has helped many thousands of people better understand concepts that they would otherwise struggle with. No matter who you are or what you do, the table has played some role in your life, directly or indirectly.