"Using the Bohr model, we can determine the number of valence electrons an atom has. The valence electrons are the electrons in the outermost energy level (shell) of an atom, which are responsible for the atom's chemical behavior.
Elements in the same group (column) on the periodic table have the same number of valence electrons. For example, all elements in Group 1 (the alkali metals) have one valence electron, while all elements in Group 2 (the alkaline earth metals) have two valence electrons.
In the Bohr model, the number of valence electrons is equal to the number of electrons in the outermost shell. For example, in the Bohr model of hydrogen, there is one electron in the first energy level (shell), which is also the valence electron.
Therefore, if two elements have the same number of valence electrons in their Bohr models, they are in the same group (column) on the periodic table.
On the other hand, elements in the same period (row) on the periodic table have the same number of energy levels (shells). For example, all elements in the second period (row) have two energy levels (shells), while all elements in the third period (row) have three energy levels (shells).
In the Bohr model, the number of energy levels is equal to the number of shells or orbits around the nucleus. For example, in the Bohr model of helium, there are two electrons in the first energy level (shell) and no electrons in the second energy level (shell), which means that helium is in the first period (row) of the periodic table.
Therefore, if two elements have the same number of energy levels in their Bohr models, they are in the same period (row) on the periodic table." (ChatGPT, 2023)