Final answer:
The "+1" on the periodic table signifies that elements in the first group, like H, Li, and Na, usually form cations with a +1 ionic charge due to the loss of one valence electron.
Step-by-step explanation:
The number "+1" written on the periodic table above the period that contains H, Li, and Na indicates the ionic charge that elements in that group typically form. Elements such as hydrogen (H), lithium (Li), and sodium (Na), which are located in the first group of the periodic table, have one valence electron they tend to lose when forming ions. Consequently, they commonly form cations with a +1 charge.
The periodic table is a tool that organizes elements by their atomic number and groups them based on similar properties, including their tendency to form certain ions. For instance, the second group contains alkaline earth metals such as beryllium (Be) and magnesium (Mg), which tend to form ions with a +2 charge. On the opposite end of the periodic table, the halogens in the next-to-last column, like fluorine (F) and chlorine (Cl), typically form anions with a -1 charge. This systematic arrangement helps in predicting the behavior of elements during chemical reactions.