Synthetic elements are radioactive and decay rapidly into lighter elements—possessing half-lives so short, relative to the age of the Earth (which formed 4.54 billion years ago), that any atoms of these elements that may have existed when the Earth formed have long since decayed. Atoms of synthetic elements only occur on Earth as the product of atomic bombs or experiments that involve nuclear reactors or particle accelerators, via nuclear fusion or neutron absorption.
Atomic mass for natural life is based on weighted average abundance of natural isotopes that occur in the Earth's crust and atmosphere. For synthetic elements, the isotope depends on the means of synthesis, so the concept of natural isotope abundance has no meaning. Therefore, for synthetic elements the total nucleus count (protons plus neutrons) of the most stable isotope, i.e. the isotope with the longest half-life—is listed in brackets as the atomic mass.
Not all radioactive elements are synthetic. For instance, uranium and thorium have no stable isotopes but occur naturally in the Earth's crust and atmosphere. Unstable elements such as polonium, radium, and radon—which form through the decay of uranium and thorium—are also found in nature, despite their short half-lives.
Read more about this topic: Synthetic Element
Famous quotes containing the word properties:
“A drop of water has the properties of the sea, but cannot exhibit a storm. There is beauty of a concert, as well as of a flute; strength of a host, as well as of a hero.”
—Ralph Waldo Emerson (18031882)
“The reason why men enter into society, is the preservation of their property; and the end why they choose and authorize a legislative, is, that there may be laws made, and rules set, as guards and fences to the properties of all the members of the society: to limit the power, and moderate the dominion, of every part and member of the society.”
—John Locke (16321704)