Periodic table structure

In 1869, Russian scientist Mendeleev designed the periodic table used today. The elements were ordered by their atomic number and grouped by their physiochemical properties. This allows scientists to predict how theoretical undiscovered elements will act. The periodic table got its name from the periods (rows) in the table which show common trends in atomic structure and properties.

The columns of the periodic table are called groups, they each have their own number and name. Elements in the same group have very similar properties because they have the same number of electrons in their outer shell. As you go down a group, the elements get bigger as they gain an extra shell of electrons.

The rows in the Periodic Table are called periods, they are numbered and represent how many shells of electrons an element has. As you move across a period, the nuclear charge gets bigger but the size of the atom gets smaller.

Where an element is found in the periodic table can tell you a lot about its physical and chemical properties. Most elements are metals, but the top right corner of the periodic table is reserved for non-metals. An element’s group indicates how many electrons are in the outer shell, this helps to determine the ionic charge. Metals form positive ions with the charge of their group number. Non-metals form negative charges with the charge of their group number - 8.

Each period consists of sublevels that can be filled with a certain number of electrons. To illustrate this, the periodic table can be split into blocks, s, p, d and f. The block and period an element is found in shows which sublevel the valence electrons are stored in. Aluminium (Al) would have valence electrons in sublevel 3p, with an electron configuration = 1s²2s²2p⁢3s²3p¹. A shorthand way to write the electron configuration is starting from the noble gas before, eg [Ne]3s²3p¹ for Aluminium.


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