Barium (Ba) is an element in the periodic table, and its ion has a formula of Ba2+. To identify the group of the periodic table that this element belongs to, we need to understand the organization of the periodic table and how ions are formed.

Organization of the periodic table:
- The periodic table is a tabular arrangement of chemical elements, organized based on their atomic number, electron configuration, and recurring chemical properties.
- The elements are grouped into periods (horizontal rows) and groups (vertical columns).

Formation of ions:
- An ion is an atom or molecule that has gained or lost electrons, resulting in a positive or negative charge.
- Cations are positively charged ions that are formed when an atom loses electrons.
- Anions are negatively charged ions that are formed when an atom gains electrons.

Explanation:
- The formula Ba2+ indicates that the barium ion has a charge of 2+, meaning it has lost two electrons.
- The atomic number of barium is 56, which means it has 56 electrons in its neutral state.
- By losing two electrons, the barium ion (Ba2+) now has 54 electrons.
- Barium belongs to Group 2 of the periodic table, also known as the alkaline earth metals group.
- Group 2 elements have two valence electrons in their outermost energy level.
- By losing these two valence electrons, barium achieves a stable electron configuration similar to that of a noble gas (neon).
- The elements in Group 2 have similar chemical properties due to their shared valence electron configuration.

Conclusion:
Based on the given formula Ba2+, the element barium (Ba) belongs to Group 2 of the periodic table. Group 2 elements are known as alkaline earth metals and have two valence electrons in their outermost energy level.