Periodic Table and periodicity - Andhra Pradesh PCS Exam Notes

Periodic Table and periodicity

Criteria for a new element discovery

Assessing if an element has been “discovered” is not a simple task. While reviewing the discovery profiles of the transfermium elements in the early 90s’, IUPAC and IUPAP set up to establish a series of criteria that must be satisfied for the discovery of an element to be recognized.

Temporary name and symbol

While an element can have been claimed, before the claim has been validated and before the element is formally named, the element has a temporary name and symbol.

Validation and assignation of an element discovery

Claims for the discoveries of new elements appear time to time in the scientific literature. IUPAC, along with IUPAP, is involved in assessing these claims. In result, IUPAC technical reports are released that review each pertaining references and recognize the laboratory whose claims fulfill the agreed criteria.

Naming new element

When the discovery of a new element has been validated and the priority for its discovery has been assigned, the naming process can begin. The Laboratory to which the discovery has been assigned is invited to propose a name and symbol. IUPAC will then review the proposal, and if agreed, after an additional 5-month public review, will formalize the name.

Periodicity

Periodicity refers to trends or recurring variations in element properties with increasing atomic number. Periodicity is caused by regular and predictable variations in element atomic structure.

Mendeleev organized elements according to recurring properties to make a periodic table of elements. Elements within a group (column) display similar characteristics. The rows in the periodic table (the periods) reflect the filling of electrons shells around the nucleus, so when a new row begins, the elements stack on

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Periodicity was helpful to Mendeleev because it showed him gaps in his periodic table where elements should be. This helped scientists find new elements because they could be expected to display certain characteristics based on the location they would take in the periodic table. Now that the elements have been discovered, scientists and students used periodicity to make predictions about how elements will behave in chemical reactions and their physical properties. Periodicity helps chemists predict how the new, superheavy elements might look and behave.

Periodicity can include many different properties, but the key recurring trends are:

This is the energy needed to completely remove an electron from an atom or ion. Ionization energy increases moving left to right across the table and decreases moving down a group.

A measure of how readily an atom forms a chemical bond. Electronegativity increases moving left to right across a period and decrease moving down a group.

This is half the distance between the middle of two atoms just touching each other. Atomic radius decreases moving left to right across a period and increases moving down a group. Ionic radius is the distance for ions of the atoms and follows the same trend.

This is a measure of readily an atom accepts an electron. Electron affinity increases moving across a period and decreases moving down a group. Nonmetals usually have higher electron affinities than metals.