Dmitri Mendeleev developed a chart-like arrangement of the elements called the 18 . He stated that if the elements were listed in order of increasing 5 , their properties repeated in a regular manner. He called this the 17 of the elements. The arrangement used today differs from that of Mendeleev in that the elements are arranged in order of increasing 6 . Each horizontal row of elements is called a(n) 16 . Each vertical column is called a(n) 9 , or, because of the resemblance between elements in the same column, a(n) . In rows 4 through 7, there is a wide central section containing elements, each of which is called a(n) . Rows 6 and 7 also contain two other sets of elements that are listed below the main chart. These are called the __ and the , respectively. Each of the elements to the left of the stairstep line of the chart, is classified as a(n) __ . Each of the elements at the right side of the stairstep line is classified as a(n) . Each of the elements between these two main types, having some properties like one type and other properties like the other type, is called a(n) . Each of the elements in the column labeled IA or 1 is called a(n) . Each of the elements in the column labeled IIA or 2 is called a(n) . Each of the elements in column VIIA or 17 is called a(n) . Each of the elements in column VIIIA or 0 or 18 is called a(n) .