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 arrangement of the elements is known as the Periodic Table of Elements and is arranged according to the atomic number of elements. Note that an element: 1  consists of only one kind of atom, 2  cannot be broken down into a simpler type of matter by either physical or chemical means, and. 3  can exist as either atoms (e.g. argon) or molecules (e.g., nitrogen).