In a color-coded periodic table of the elements, the box for each element is colored. This color represents the classes of elements, which include metals, metalloids and non-metals. In general, the color blue is used for metals, orange for metalloids and green for non-metals. The periodic table may be further color-coded to include other groups such as transition metals, rare earths, alkali metals, alkaline earths, halogens and noble gases.
The modern periodic table organizes elements by their atomic number, which is unique to each element. The atomic number represents the number of protons in an atom of the element. In the modern periodic table, the atomic number increases from left to right and from top to bottom. The periodic table is also organized into periods and groups. Periods are the rows and groups are the columns. The elements in each period begin with metals on the left side, then move to metalloids and then to nonmetals on the right. The elements contained in each group have similar physical properties. For instance, all elements in group 18 are considered colorless, odorless gases. Groups and periods may have different numbers of elements within them. Overall, the modern periodic table contains more than 110 elements.