What are the main features of the periodic table?

Expert Answers

An illustration of the letter 'A' in a speech bubbles

Most versions of the periodic table share the same basic information;

  • Each square represents an element, with that element's symbol printed in a font size larger than any other information. The full name of the element is often written above or below it. 
  • The molar mass of the element is usually printed below the name, to varying degrees of specificity. 
  • The number of protons in the element is printed somewhere at the top of the square.
  • Some tables also print the abbreviated electron configuration, color-code the metallic classifications, and/or print the numbers of the periods and groups.

However, the format of the periodic table is what really distinguishes this information, with the exception of the lanthanide and actinide series, which are typically printed below the main body of the table for no other reason than that their inclusion in their proper place would make the table unreasonably wide and difficult to scale legibly. Other than this concession, the table is arranged roughly in order of which orbital electrons go into as the atoms get progressively more massive. This is the main reason for the "gaps" as well as the apparent inconsistencies in orbital filling in heavier atoms (for example, 3d being filled after 4s despite belonging to a "lower" shell). A side effect of this arrangement is that it prioritizes noble gases on the far-right column, and allows for convenient trends such as atomic size, electronegativity and metallic character to be visually correlated to a physical location on the table. 

Approved by eNotes Editorial Team