Blocks
A block of the periodic table of elements is a set of adjacent groups. The respective highest-energy electrons in each element in a block belong to the same atomic orbital type. Each block is named after its characteristic orbital: s, p, d, f, g (no elements belonging to the g-block have been observed).

The four blocks are s, p, d, and f. Elements in each block are colour coded in the background graphics, the periodic tables, and the element pages themselves. To see these colours, however, you need browser software with capable of shading the cells in a table. If you do not see these colours, please upgrade your browser software.
Groups 1-2 (except hydrogen) and 13-18 are termed main group elements.
Groups 3-11 are termed transition elements. Transition elements are those whose atoms have an incomplete d-subshell or whose cations have an incomplete d-subshell.
Main group elements in the first two rows of the table are called typical elements.
The first row of the f-block elements are called lanthanoids (or, less desirably, lanthanides. The second row of the f-block elements are called actanoids (or, less desirably, actanides.
All About the Periodic Table
The periodic table, also known as Mendeleev's table, is a table of the chemical elements existing on Earth. The Russian chemist Dmitri Mendeleev is credited with its creation in 1869, although less extensive tables existed before this. He intended to display the patterns apparent in the chemical properties of each element. Since its original creation, new elements have been discovered and added to Mendeleev's initial table.
STRUCTURE
The structure of the periodic table is very significant. The current table holds 117 elements in a very distinct order for the purpose of showing similarities and differences in chemical properties. Out of all of the elements, 94 are found in nature and the other 24 were synthetically produced with particle accelerators. As well, most copies of the periodic table separate the metal and non-metal elements with a dark stair-step line. The metals are on the left and the non-metals on the right. Additionally, elements are placed in order of increasing atomic number, which is the number of protons in the nucleus of the element's atom. The rows are also organized so that elements with similar properties are found in the same columns. Within