Definition

• The periodic table of the elements is basically an arrangement of all known elements. Several properties of each element determines its configuration, like number of protons and electrons, along with its atomic weight. The table is a vital reference for all types of chemical research, since an element's place on the table can tell a chemist several pieces of vital information.
  
  

History

• The table is unofficially attributed to Dmtri Mendeleev, a Russian chemist who first published the table in the mid 19th century. The claim is unofficial, however, because several chemists before him contributed to the formation of the table by examining the properties of elements and the patterns they form. The table had been being formed for several years beforehand, Mendeleev was simply the first to make it official.
  
  

Periods

• The rows of the periodic table are commonly called periods, giving the table part of its namesake. The period number is determined by the highest energy level of an electron in the element. Elements in the same period are not necessarily sharing the same properties; often, the left side of the row contains active solids while the right side is made up of inactive gases. The period number increases as you move down (left to right) the table.
  
  

Groups or Families

• The columns of the table are often called groups, or families. There are 18 groups in the table. They are determined based on the specific electron configuration, so if two elements are in the same column the have the same valence electron configuration. This basically means that these two elements will behave similarly in chemical reactions.
  
  

Reading

• Hydrogen
  
  Each box in the periodic table has the same structure and can be read the same way. First, the very top number is called the atomic number. It refers to the number of protons in one atom of that element. This progresses down the table, with hydrogen (pictured) being first. Next, the central letter is the abbreviation for the element represented. Some are intuitive, like H meaning hydrogen. Some are not, like K meaning potassium. The lowest number is the atomic weight, which is the weight of one atom of the element.