The periodic table of elements is extremely useful to chemists because it allows them to readily access a lot of information about the elements in two different ways.  One way is simply reading the numbers off of the table that are associated with each element.  We can get the atomic number (number of protons) and atomic weight (number of grams per mole) of each element because it is printed directly on the table for each element block.  Chemists calculate molecular weights for chemicals quite often, so having all of this information in one place is quite useful.  The other way that the periodic table is helpful is in seeing atomic and chemical trends by seeing where different elements are placed on the table.  The shape of the periodic table and the position of the elements relative to each other is not random.  Instead, it is based on a variety of factors and the positions of the elements helps chemists to see that the reactivity is for different elements, what types of ions they form, what type of electrons they have, and other types of trends like atomic radius and electronegativity.  It also helps students see all of this information to help them with understanding concepts and answering exam questions!