Those elements that fill the 5f orbital. Because actinium—which does not fill the 5f orbital—exhibits characteristics similar to those of the actinides, it is usually considered part of the actinidesfamily. Of the other 14 actinides, usually shown at the bottom of the periodic table, only the first three occur in nature.
The number of protons in the nucleus of an atom. Since this number is different for each element, elements are listed on the periodic table of elements in order of atomic number.
A term used to describe the pattern formed by orbitals.
The length of time it takes a substance to diminish to one-half its initialamount. For a sample of radioisotopes, the half-life is the amount of time it takes for half of the nuclei to become stable isotopes. Half-life can be a few seconds; on the other hand, for uranium-238, it is a matter of several billion years.
The lanthanides and actinides, which are unique in that they fill the f orbitals. For this reason, they are usually treated separately.
Atoms that have an equal number of protons, and hence are of the same element, but differ in their number of neutrons. This results in a difference ofmass. Isotopes may be either stable or unstable. The unstable type, known as radioisotopes, are radioactive.
The transition metalsthat fill the 4f orbital.
The sum of protons and neutrons in the atom's nucleus. The designation 238 U, for uranium-238, means that this particular isotope of uranium has a mass number of 238. Since uranium has an atomic number of 92, this means that uranium-238 has 146 neutrons in itsnucleus.
A subatomic particle that has no electric charge. Neutrons are found at the nucleus of an atom, alongside protons.
The center of an atom, a region where protons and neutrons are located, and around which electrons spin. The plural of "nucleus" is nuclei.
A region of probabilities regarding the position of an electron for anatom in a particular energy state. The higher the principal energy level, the more complex the pattern of orbitals.
A value indicating the distance that an electron may move away from the nucleus of anatom. This is designated by a whole-number integer, beginning with 1 and moving upward. The higher the principal energy level, the greater the energy in the atom, and the more complex the pattern of orbitals. Elements in the transition metal family have principal energy levels of 4, 5,6, or 7.
In a general sense, radiation can refer to anything that travels in astream, whether that stream be composed of subatomic particles or electromagnetic waves. In a more specific sense, the term relates to the radiation from radio active materials, which can be harmful to humanbeings.
A term describing a phenomenon whereby certain isotopes, known as radioisotopes, are subject to a form of decay brought about by the emission of high-energy particles. "Decay" does not mean that the isotope "rots"; rather, it decays to form another isotope until eventually (though this may take a long time) it becomes stable.
An isotope subject to the decay associated with radioactivity. A radioisotope is thus an unstable isotope.
A region within the principal energy level occupied by electrons in anatom. Whatever the number n of the principal energy level, there are n sublevels. Actinides are distinguished by the fact that their valence electrons are in a sublevel corresponding to the 5f orbital.
A group of 40 elements (counting lanthanum and actinium), which are the only elements that fill the d orbital. In addition, the transition metals have their valence electrons on two different principal energy levels. Though the lanthanides and actinides are considered inner transition metals, they are usually considered separately.
Elements with an atomic number higher than that of uranium (92). These have all have been produced artificially. The transuranium elements include 11 actinides, as well as 9 transition metals.
Electrons that occupy the highest principal energy level in an atom. These are the electrons involved in chemical bonding.
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