Period 7 of the periodic table
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Period 7 is the seventh row of the periodic table of chemical elements. It begins with francium (atomic number 87) and ends with oganesson (atomic number 118). All elements in this period are radioactive, meaning their atomic nuclei decay and transform into other elements over time.
The period contains 32 elements, the same number as period 6. This is because the electron shells designated 7s, 5f, 6d, and 7p must be filled. The filling of the 5f shell produces a group of elements called the actinides, which run from actinium (89) to lawrencium (103) and are typically shown separately below the main table.
Elements in this period
The period begins with francium, an alkali metal, and radium, an alkaline earth metal. These are followed by the actinides, which include thorium, uranium, and plutonium. After lawrencium come transition metals such as rutherfordium, dubnium, and seaborgium, ending with the period 7 elements that conclude with oganesson.
Superheavy elements
Elements with atomic numbers greater than 103 are called superheavy elements. They do not occur in measurable amounts in nature; they are made in nuclear research centers by bombarding atoms with a high-energy particle accelerator. Their lifespans are typically fractions of a second or shorter, so study of their chemical properties relies on experiments conducted with only a few atoms.
General properties
Period 7 elements have nuclei with many protons, which reduces nuclear stability. As atomic number increases, relativistic effects from fast-moving inner electrons alter the expected properties, so their chemical behavior sometimes differs from that of other elements in the same group.