Periodic table

The periodic table is a way of displaying the chemical elements so that the electronic properties of each element resemble all of those above and below it. Look at the leftmost column below. Lithium, sodium, potassium and the rest are all low-melting metals with good electrical conductivity, which almost always donate one electron in chemical interactions, and which react violently with water. Hydrogen, too, meets some of those criteria, although it's a freak in any system. Moving downward, row by row, the elements get larger because the table is arranged by atomic number, reading from left to right and top to bottom. The columns are called groups, or sometimes families; and they go and they're numbered 1 to 18. The rows are called periods, and they're numbered from 1 to 7. To paraphrase Randall Munroe's "What If": Do not build the 8th row.

Wikipedia has an excellent periodic table, which can be accessed via the article on any element, and which, via that element's isotopes, to a table which can pull up a list of any element's isotopes. This wiki's tables tend to focus on elements which have not yet been observed.

The types of periodic tables are:

• Standard periodic table: The periodic table with actinides and lanthanides on the bottom.
• Expanded periodic table: The periodic table with the actinides and lanthanides in the middle.
• Extended periodic table: A larger version of the standard periodic table.