A period 9 element is one of the chemical elements in the ninth row (or period) of the periodic table of the elements. None of these elements has yet been created. A chemical element, often called simply element, is the class of atoms which contain the same number of protons. ... In the periodic table of the elements, a period is a row of the table. ... The periodic table of the chemical elements, also called the Mendeleev periodic table, is a tabular display of the known chemical elements. ...
A period 1 element is one of the chemical elements in the first row (or period) of the periodic table of the elements. ... A period 2 element is one of the chemical elements in the second row (or period) of the periodic table of the elements. ... A period 3 element is one of the chemical elements in the third row (or period) of the periodic table of the elements. ... A period 4 element is one of the chemical elements in the fourth row (or period) of the periodic table of the elements. ... A period 5 element is one of the chemical elements in the fifth row (or period) of the periodic table of the elements. ... A period 6 element is one of the chemical elements in the sixth row (or period) of the periodic table of the elements, including the Lanthanides. ... A period 7 element is one of the chemical elements in the seventh row (or period) of the periodic table of the elements. ... A period 8 element is one of the chemical elements in the eighth row (or period) of the periodic table of the elements. ...
Periodic tables The periodic table of the chemical elements, also called the Mendeleev periodic table, is a tabular display of the known chemical elements. ...
The periodic table is the most important reference a chemist has because it puts all the known elements into a meaningful pattern.
The period number of an element signifies the highest energy level an electron in that element occupies (in the unexcited state).
The number of elements in a period increases as one moves down the periodic table because as the energy level of the atom increases, the number of energy sub-levels per energy level increases.