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Development of Periodic Table

The end of the periodic table: End of the periodic table ? As the relative speed increases, the mass appears to increase. The relativistic mass becomes closer to infinity when the speed of the object approaches speed of light. Many theoretical calculations interpret that the velocity of 1s electron of element untriseptium (a theorized chemical element that is predicted to be a synthetic element of Z=137) approaches the velocity of light. If this element may actually be discovered, it may be renamed to feynmanium (symbol Fy) after Richard Feynman, an American theoretical physicist, who suggested that the neutral atoms cannot exist beyond this element. He made this statement based on simplistic interpretation of the relativistic Dirac equation which runs into problems with electron orbitals at Z > (1/α) = 137, and that a periodic table of elements based on electron orbitals therefore breaks down at this point. A more rigorous analysis calculates the limit to be Z ≈ 173, but also that this limit would not actually spell the end of the periodic table.

Learning Objectives

After completing the topic, the student will be able to:

  • Write electronic configuration of neutral elements or ions by using the building up principles.
  • Explain the exceptions in electronic configuration of certain elements by using Hund's rule of maximum multiplicity.
  • State Newland's law of octaves and recognize the similarity of properties of every 1st and 8th element in Newland's series of elements.
  • Appreciate how the concept of grouping elements in accordance to their properties led to the development of periodic table.
  • Discuss the merits and demerits of various methods of grouping elements and understand how modern periodic arrangement describes the drawbacks of its earlier periodic arrangement.
  • Understand the periodic laws and significance of atomic number and electronic configuration as the basis of periodic classification.
  • Identify and group the given elements in the modern periodic table with the help of electronic configuration or atomic number.
Electronic configuration of IA group elements Electronic configuration of IA group elements Arrangement of electrons in the shells according to their energy levels is called as electronic configuration. Electronic configuration of alkali metals is shown here with addition of outer shell with increase in their number of electrons.
Periodic Table

The arrangement of electrons in the orbitals of an atom is called the atom's electronic configuration. The electronic configuration of any atom can be shown in an energy‐level diagram by placing that atom's electrons in the orbitals in the order of increasing energy level. The pairing of electrons of opposite spin in an orbital takes place only when necessary. An abbreviated way of presenting electronic configuration is to write the principal quantum number and letter of each occupied orbital and then use a superscript to indicate number of electrons in each orbital. The orbitals of each atom are then written in the order of increasing energy levels as shown in adjacent figure.

The electrons filling different atomic energy levels or shells, is neatly given by Aufbau principle, shown in the figure below. All the superscripts for an atom must add up to the total number of electrons in the atom: 1 for hydrogen, 3 for lithium, 11 for sodium, and so on. The orbitals are not always listed in order of principal quantum number. The 4s orbital, for example, is lower in energy than the 3d orbitals as is indicated on the energy level diagram. The 4s orbital, therefore, appears before the 3d orbital.

Lavoisier's table of elements Lavoisier's table of elements At the end of the 18th century, Lavoisier tabulated a list of the 33 elements and simple compounds known at that time.
History of periodic table

At the end of the 18th century, Lavoisier tabulated a list of the 33 elements and simple compounds known at that time. By 1870, 65 elements were discovered and tabulated by D. Mendeleev and others. Today there are 116 elements to understand the properties of matter. These elements combine to form millions of compounds, some of the elements have similar properties, so there is need of organization of these elements to understand their behavior. Before going to understand the extended form of periodic table here is a discussion of early organization of elements.

The elements shown in the table were the agreed upon elements at the time of Lavoisier. The names in the right purple column were listed as elements but Lavoisier suspected that they weren't elements; he just couldn't get them to decompose. Later, lime was shown to be calcium combined with oxygen. Magnesia consisted of magnesium, sulfur and oxygen. Silex and Argill were also found not to be elements but made up of true elements.

Dalton suggested that substances around us were made up from a grouping of specific number of atoms of different elements. This idea would tremendously simplify the complexity of all the materials around us. For example, a water molecule is made from two atoms of hydrogen and one atom of oxygen. If there are 2 oxygen atoms and 2 hydrogen atoms in a molecule then it is not water but something else. Salt is made from one sodium atom and one chlorine atom. Ammonia is made from 3 hydrogen atoms and one nitrogen atom.

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