The periodic table is organized with elements in the same column having the same arrangement of electrons. This means that elements in the same column also have the same number of valence electrons. Certain columns in the periodic table are named according to the distinctive properties of those elements. For example, group 8A elements are called noble gases. Noble gases are particularly stable because they have filled s and p subshells for their outermost shell. Elements without a noble gas configuration tend to gain, lose, or share electrons to obtain a similar electron configuration as their nearest noble gas. The elements in the periodic table can also be categorized as metals, nonmetals, and metalloids. Metals are in the lower left of the periodic table, nonmetals are in the top right, and metalloids separate them. Metals have distinctive properties. They are generally malleable (which means they can be hammered into sheets), ductile (which means they can be pulled into wires), shiny, solids at room temperature, and good conductors of heat and electricity. In reactions, metals tend to lose electrons to obtain a more stable electron configuration. Nonmetals, on the other hand, tend to be poor conductors of heat and electricity. In reactions, nonmetals tend to gain or share electrons to obtain a more stable electron configuration. Another group in the periodic table with distinctive properties is group 1A. These metals are called alkali metals. They're highly reactive and tend to lose one electron when forming an ionic compound because they have one electron in their outermost s subshell. Group 2A elements are called alkaline earth metals. These metals are slightly less reactive than alkaline metals and tend to lose two electrons when they react because they have two electrons in their outermost s subshell. Group 7A elements are called halogens. When they react, they tend to accept one electron when forming an ionic compound because they have five electrons in their outermost p subshell, or they will share electrons to form a covalent compound. So we can use an element's position in the periodic table to predict what charge it will form in an ionic compound. Our halogens in group 7A form a 1- ion because they need one additional electron to have the same electron configuration as their nearest noble gas. Group 6A tends to gain two electrons because they need two additional electrons to have the same electron configuration as their nearest noble gas. Our alkaline metals, on the other hand, tend to lose one electron to have the same electron configuration as their nearest noble gas. And our alkaline earth metals in group 2A tend to lose two electrons.