APA stands for American Psychological Association. APA is often called name-and-date style. APA Format is widely used in psychology, business, education, engineering and the social sciences.The latest APA manual is called: Publication Manual of the American Psychological Association, sixth edition.
The elements are arranged in order of their increasing atomic number. Also the columns or groups are arranged by the number of valence electrons that a element has. For example, all the elements in column 1 have 1 valence electron meaning it has 1 electron in its outer shell. Elements in the same column tend to have similar if not identical properties.
The Periodic Table is an arrangement of the elements in order of atomic number. Columns in the table - groups. The elements in any one vertical column are said to be in the same group or family. Eight of the groups are numbered from left to right. Elements in the same group have similar chemical properties. The group number is the same as the number of electrons in the outer shell of all the elements in the group.