History of the Periodic Table: Difference between revisions

Almost all of the credit for the periodic table goes to Dmitri Mendeleev. He arranged the elements by their atomic mass, like Newlands, but he did something different. He added in the elements that had not been discovered yet. He decided to do this because while he was studying the atomic masses he noticed that when they were put in order some of them increased more than others. <ref name=BJU/> He also arranged them vertically <ref>BBC. [http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/atomic_structure/periodictablerev1.shtml Atoms and the periodic table] ''BBC Science''. Accessed May 21, 2017.</ref>, and added the transition metals. He recognized that the transition metals did not fit into the chart so he separated them from the rest of the periodic table. Mendeleev summarized his work by writing the periodic law. The law states, ''The properties of elements vary with their atomic masses in a periodic way.'' <ref name=BJU/>

Although Mendeleev's periodic table was brilliant, there were still some things wrong about it. The way that the elements were arranged still did not always group the elements that were similar. One of Ernst Rutherford's assistants, Henry Moseley, suggested that they develop a way to count the number of protons in an atom's nucleus. Once he created a way to do this, he realized they needed to revise the periodic table to make it more accurate, now that they could find the number of protons in an atom. He changed the periodic table and the periodic law. The modern periodic law states, ''The properties of elements vary with their atomic numbers in a periodic way''. <ref name=BJU/>  

The only large addition to the Periodic Table was after World War II. The experiments with nuclear energy created heavy elements. These elements created in man-made nuclear reactions were called transuranium elements. They were given this name because their atomic numbers are greater than uranium's atomic number. Neptunium and plutonium are the only transuranium elements found in nature. The rest of them are products of the nuclear reactions. <ref name=BJU/>

The modern periodic table has more than the 63 elements that were discovered by Mendeleev. Most of the periodic tables up to this date have up to 109 elements. It has 18 groups in vertical columns. The vertical columns are labeled by roman numerals or numbers, and each horizontal row is called a period, and the periodic table consists of seven periods. <ref>GENESIS. [https://genesismission.jpl.nasa.gov/educate/scimodule/cosmic/explore_2ST.pdf Cosmic Chemistry: An Elemental Question] ''Genesis Education''. Accessed May 21, 2017.</ref> On the left and middle side of the table there are the elements that are metals. On the right side are the nonmetals, groups 13-18. The metalloids are adjacent to the stair-step line on the table. On the bottom of the table are the tow rows of elements called the lanthanide series and the actinide series. The atomic number increases from left to right along the whole periodic table, and become less metallic.

There are distinct families in the periodic table. One example is the alkali metal family. It consists of all the elements in the periodic table that are very chemically reactive. The elements are lithium, sodium, potassium, rubidium, cesium, and francium. These metals conduct electricity easily and have a bright and shiny surface. They all react easily with water. Alkali metals are most commonly used in streetlights, soap, rayon, and paper. There are many different families. The others are: alkaline-earth metals, transition metals, post-transition metals, metalloids, nonmetals, halogens, and noble gases. <ref name=BJU/>