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A team at Lawrence Berkeley National Laboratories reported the discovery of elements 116 and 118 in June 1999.

The same team retracted the discovery in July 2001. The discovery of elements 113,114, and 115 has been reported but not confirmed.

The atomic masses listed in this table reflect the precision of current measurements. (Values listed in parentheses are the mass numbers of those radioactive elements' most stable or most common isotopes.)

A BIOLOGIST'S GUIDE TO THE PERIODIC TABLE

The classification system used in this book is based on both the commonly recognized six-kingdom system and the newer, three-domain system. A kingdom is a group of related phyla, whereas a domain is a larger-scale grouping that can encompass kingdoms. In the three-domain system, all living organisms are classified into one of three domains based on cellular similarities. Two of the three domains consist of prokaryotes, and one domain consists of eukaryotes. The table below compares the two systems of classification.

The domain Bacteria aligns with the kingdom Eubacteria. The domain Archaea aligns with the kingdom Archaebacteria. Both archaea and bacteria are prokaryotic microbes, although the two groups differ significantly.

The third domain, Eukarya, consists of all of the eukaryotic organisms. The four kingdoms that align with the domain Eukarya are Animalia (animals), Plantae (plants), Fungi (fungi), and Protista (protists).

The information on the following pages is conveniently organized into commonly recognized subgroups. However, not all of the existing subgroups are presented here, and all classifications are sometimes debated and revised by the scientific community. For example, biologists have proposed several new kingdoms to replace Protista, because the subgroups of Protista are no longer thought to be strongly related. Also, scientists are still uncertain about the number of species in each group.

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