Periodic Table

The system of periodic elements was first invented by a Russian chemist by the name of Dmitri Ivanovich Mendeleev. Dmitri Mendeleev. He placed the periodic elements in vertical columns and sorted them by the repeatability of their chemical and physical properties. However, there were many white spots in his Periodic Table.

Later, with the help of many others, Mendeleev discovered the missing elements. Years later, a British physician, Henry Moseley, identified the nuclear masses in each element and arranged them in order from smallest to largest. This is what we call the modern periodic table today. The modern periodic system is composed of all elements ordered in ascending atomic number (periodic table). There are seven periods or horizontal rows of the periodic table. There are 9 periods in total. Vertical columns are called groups. They are denoted by letters from 1A to 7A. There are four different categories elements can be placed into depending on their electron configuration.

The first is noble gases; this is Group 0. Noble gases are elements that have outermost s and p levels fill. For example, Helium is 1s2 and Argon is 1s 2s22p°3s23p° . Representative elements are usually called the Group A elements. Representative elements are elements whole outermost s and p sublevels are only half filled. For example, Lithium is 1s 2s1 and Potassium is 1s 2s 2p 3 s2 3 p° 4 s’ It includes alkali metals, alkaline earth metals and halogens. Group B elements are called transition elements. The transition metals are elements whose outermost s sublevel and the nearby d sublevel contain electrons.

They are defined by having electrons added to the d orbitals. Lastly, the inner transition metals are elements whose outermost s sublevel and the nearby f sublevel usually contain electrons, identified by the filling of f orbitals. The atomic radius is half the distance between the nuclei of two like atoms. Although, it can only be found if the elements that exist as diatomic molecules. When you move down the periodic table atomic size usually increases. Although, it usually decreases when you move from left to right across a period (horizontally). Ions are formed when an atom gains or loses an electron. Ionization energy is the energy required to remove an electron from its gaseous form. In general, the ionization energy decreases as you move down a group. Although, for representative elements, or Group A, generally increases when you go from left to right across a period.

Electronegativity is the tendency for the atoms of the element to attract electron when they are chemically combined with another element. It is indicated in arbitrary units on the Pauling electronegativity scale. When you go across a period from left to right, the electronegativity increases. All of these elements make up the periodic table. Without it we would not have the periodic table of elements today. This is what we call today the Modern periodic table.