How does the periodic table work-?

Answer 1

The layout of the Periodic Table demonstrates recurring ("periodic") chemical properties. Elements are listed in order of increasing atomic number (i.e. the number of protons in the atomic nucleus). Rows are arranged so that elements with similar properties fall into the same vertical columns ("groups"). According to quantum mechanical theories of electron configuration within atoms, each horizontal row ("period") in the table corresponded to the filling of a quantum shell of electrons. There are progressively longer periods further down the table, grouping the elements into s-, p-, d- and f-blocks to reflect their electron configuration. In printed tables, each element is usually listed with its element symbol and atomic number; many versions of the table also list the element's Atomic Mass and other information, such as its abbreviated electron configuration, electronegativity and most common valence numbers. Hope this helps.

Answer 2

Mendeleev's periodic table predicted three elements of atomic weights 45, 68 and 70. He was proven right when these elements were later discovered and identified as scandium, gallium and germanium, respectively. The atomic weights listed in modern periodic tables are slightly different than those in Mendeleev's time because methods for measuring atomic weights were improved during the 20th century. These discoveries demonstrated the usefulness of Mendeleev's approach, even if it wasn't without problems. Explanations would have to wait until the early 20th century, when the structure of the atom began to be revealed. In 1911, English chemist Henry Moseley studied the frequencies of X-rays given off by various elements when high-energy electrons bombarded each. The X-rays each element emitted had a unique frequency that increased with increasing atomic mass. Moseley arranged the elements in order of increasing frequency and assigned each one a number called the atomic number (Z). He realized that the atomic number was equal to the number of protons or electrons. When the elements were arranged by increasing atomic number, the periodic pattern was observed without having to switch some elements (as Mendeleev did), and "holes" in the periodic table led to the discovery of new elements. Moseley's discovery was summarized as the periodic law: When elements are arranged in order of increasing atomic number, there's a periodic pattern in their chemical and physical properties. That law led to the modern periodic table.