The periodic table is a much more interesting concept than people give it credit for. Periodic means the repeating according to some pattern. The first periodic table is very different from the modern one. They are both very interestingly organized. The periodic table has the elements on them. The first periodic table was first introduced to us in 1869 by a Russian scientist named Dmitri Mendeleev. Mendeleev studied chemistry at the University of St. Petersburg. Mendeleev’s table had many differences from the one we use today. His periodic table was in order by atomic mass. Our modern one is in order by atomic number. His also only had about 63 elements. Our modern one has 118 elements. Although there are some differences, there are also some similarities. Both …show more content…
Halogens are group 17. Halogens are highly reactive in elemental form. Even though this group only needs one electron in its outer level, it has seven electrons. When halogens are in gas form they are diatomic molecules. Diatomic molecules are two atoms in the same covalent bonds. Halogens have many different uses. Bromine, Chlorine, and Iodine are three main halogens. Bromine is the only liquid metal that is a halogen. Chlorine is the most abundant halogen. Iodine is a shiny, purple-gray solid. All three of these elements are abstracted from salt-water. Iodine is important for the human body’s diet for production of the hormones thyroxin and to prevent goiter. Goiter is the enlarging of the thyroid gland in the neck. When Iodine is heated, it turns into a purple liquid. Hydrogen is the only elements that aren’t really classified as a group. Hydrogen is at the top of the periodic table because it is the lightest element. 90% of atoms are hydrogen. Most hydrogen is in water. When hydrogen is burned in oxygen, it forms H2O. Hydrogen has a single electron and is highly reactive. Hydrogen can also gain an electron when added to an Alkali Metal or an Alkaline Earth