Question

What are common mistakes students make with the periodic table?

Answer 1

• Confusing groups and periods. Although the table itself is called the periodic table, elements in the same group (or column) are often more similar than those in the same period (row).

For example, the alkali metals (lithium, sodium, potassium, rubidium, cesium and francium) of group 1 share several properties. In their solid state, they are soft enough to be cut with a knife, and in pure form (a solid chunk of lithium, for example), they react violently with water, with the intensity of this reaction increasing as one moves down the group.

By comparison, elements in the same period have less in common. This is because elements in the same period have the same number of orbitals, or "energy levels" for their electrons. By contrast, elements in the same group have the same number of electrons in their outermost orbital; these valence electrons are a primary determinant of how an element will behave in a chemical reaction.

Another common mistake occurs when listing the electron configuration of elements. Simply put, many students forget that the 3`d` sub-orbital is filled after the 4`s` sub-orbital; it can be confusing to find sub-orbitals for one orbital being filled after the first sub-orbital for the next orbital has been filled.

Additionally, mistakes can arise surrounding the lanthanide and actinide series. Because of their placement on most versions of the periodic table outside of their expected position, many students will accidentally neglect them altogether.