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 modern periodic table is a chart containing the elements arranged in order of increasing atomic number. A vertical column, called a group, contains elements with similar properties. A horizontal row is called a period. The atomic number of the elements in a period increases from left to right along the row. Before the development of the modern periodic table, there were other attempts to arrange the elements in a useful way. For example, DÃ¶bereiner arranged groups of three elements with similar properties into âtriads'. Newlands and Mendeleev arranged the elements in order of increasing relative atomic mass.