Periodic Table properties
In chemistry, a periodic table is a tabular array of the chemical elements arranged by increasing atomic number, electron configuration, and recurring chemical properties. This arrangement shows periodic trends. The rows of the table represent groups, periods, and families of the periodic table. In this way, the table is similar to a family tree—a horizontal representation of groups of related elements. The periodic table is laid out in a grid with horizontal rows called periods and vertical columns called groups. It is a tradition to start a new group with the period's first element, which is called the element's atomic number and the first row's first element. The rows of the table are then enumerated with letters of the local standard alphabet, and the columns are numbered according to the order of the periodic table's elements within each row. The first group is one through the ninth, or groups 1 to 8, except in groups 4, 5, 6, and 7, which are numbered groups 1, 2, 3, and 7 respectively in the IUPAC version of the periodic table. In the periodic table, each horizontal row (group) and each vertical column (period) is numbered with a letter or symbol. The main section of the table is often called the "main table" or "first table" to emphasize that the elements on the main part of the table are more numerous than in other parts of the table. Periodic trends are chemical trends that are common to all elements and are believed to be largely responsible for the periodic table's organization. Each horizontal row is called a family and each vertical column is called a group. The first horizontal row (family) is one through the eighth, or families 1 to 8, except in group 3, which is called group 1. The second through fourth families are called groups 1, 2, 3, and 7 respectively in the International Union of Pure and Applied Chemistry (IUPAC) version of the periodic table. The main trends are listed below. The properties of the elements in a row or column, such as whether an element is a metal or a nonmetal and whether it is an alkali earth or alkali metal, are determined by the electron configurations, atomic radii, ionic radii, and electronegativities of the elements in that row or column. The elements are ordered by increasing atomic number, electronegativity, and ionic radius.