The periodic table is an organised array of all known chemical elements in – approximately – order of atomic weight. The table is arranged in three main ways: by group, period and block. The table’s groups are the 18 vertical columns that run from left to right. Groups are considered the most important classification method, as they stack elements that have very similar properties and trend well throughout. The table’s periods are the top seven horizontal rows on the grid running top to bottom, and partner elements across the groups that share similarities in their properties.
While groups in general hold greater similarity, certain periods hold stronger trends between elements than groups, a good example being in the transition metals. Finally, because of the importance in the classification system of the number of electrons in each element’s outer shell, the table is also broken down into four main blocks, dependent on the atomic orbital type of each element’s highest energy electrons. These are s, p, s and f-blocks respectively, and can be seen on the above table, each separated by a colour change.
Answered by Ben Gompertz. Ben is a recent graduate from the University of Birmingham with an MSci in Physics with Astrophysics. He begins a PhD course studying Gamma Ray Bursts at the University of Leicester later this year.