as we have come to understand the elements are listed on the periodic table in a way that reveals their periodicity as a result Beyond being arranged in rows or periods the elements in the same column or group will display similar properties as it was these properties that revealed the periodicity of the elements in the first place so what are these groups and what are these properties well we can see that if we exclude the lanthanides and actinides there are 18 groups on the table let's hop around the table and discuss some of these groups group one is called The Alkali Metals these all have similar reactivity because they each have one valence electron or one electron in their outermost shell as we go down the group each element has one more shell than the last as we can see from these electron configurations But whichever is the outermost shell there is only one electron in it and it is the valence electrons that determine how an element does chemistry so this explains the similarities amongst the elements of a group lithium sodium potassium rubidium cesium and francium are all highly reactive because they are all ready and willing to lose their one valence electron group two which is called the alkaline earth metals contains elements that all have two valence electrons so they also behave similarly looking at the other side of the table group 18 is the noble gases these are also known as the inner gases because they tend to be completely unreactive this is because they have a full valence shell of electrons in contrast just one group over is group 17 the halogens these are only missing one electron to fill their outermost shell so they all display a great tendency to gain one electron moving left from there we have group 16 the calcagens as well as group 15 the nictogens and the similarities in reactivity again have to do with valence electrons the number of bonds these types of atoms will form and the ratios in which they will combine with other elements are functions of the number of valence electrons so in reality the periodic table is arranged in a way that shows how elements on the left side tend to lose electrons and elements on the right side tend to gain electrons this is really all that chemistry is a sharing or transfer of electrons so that is how the periodic table is more than just a list of all the elements it is a powerful representation of the patterns that all the matter on Earth participates in