Valence Electrons
A group.
The periodic table is arranged according to the atomic structure of the elements. The atomic structure, specifically the electron arrangement determines the properties of the elements. Elements with the same outer electron configurations have similar properties and are located in the same group.
Each group has a group number.
Elements in the same period have the same number of electron shells, moving across a period (progressing group to group), elements gain electrons and protons and become less metallic. This arrangement reflects the periodic recurrence of similar properties as the atomic number increases.
Transition metals
elements in a group have the same number of valence electrons
In the Periodic Table of the Elements, a column (group) contains all elements that exist with the group number of electrons in the outer energy level of an atom of that element.
No riboflavin is not on the periodic table of elements
3rd group
There is a group of elements in the periodic table as the elements with same properties are clubbed together.
All elements in the same group have the same number of valence electrons.
The short answer is order. Elements are grouped in a table according to similarities in electron structure, atomic composition, the number of protons / neutrons / electrons. This also then naturally groups them by similar properties, metallic / nonmetallic, electronegativity, etc. Periods (columns) group by number of valence (outer shell) electrons.the basis of arrangement of element in a periodic table is based on the increasing proton number of the elements.