In 1789, Laviosier wrote Traité Élémentaire de Chimie, which is the first modern chemistry textbook. The textbook included a list of simple substances, that Laviosier believed could not be broken down any further. The list, which included oxygen, nitrogen, phosphorus, mercury, zinc, and sulfur, was a basic outline for the modern periodic table. Russian chemist, Mendeleev, was the first scientist to construct a periodic table similar to the modern version. He organized elements according to increasing atomic mass and put columns of elements together that shared physical and chemical properties. He left blank areas for unknown elements whenever there was a large gap in atomic mass between two elements. He predicted the undiscovered elements’ properties, and when they were discovered they fit perfectly in the gaps. In 1864, Meyer published his own periodic table, unknown to Mendeleev. Meyer’s table consisted of 28 elements, classified by valence electrons. Unlike Mendeleev, Meyer did not predict new elements. English chemist, Mosley, “fixed” Mendeleev’s mistake by arranging elements by increasing atomic number instead of increasing atomic mass. He’s credited for developing the modern periodic table as well as forming periodic law, which states that when elements are arranged by increasing atomic number, there is a repeating pattern of their physical and chemical properties.
According to periodic law, elements that are in the same group have the same number of valence electrons and reoccurring trends in their physical and chemical properties. The four trends caused by periodic law and valence electrons are atomic radii, ionic radii, ionization energy, and electronegativity. The first one, atomic radius, basically tells you the size of an atom. It is half the distance between two nuclei of identical atoms bonded together. As you go down a group, atomic radius