An atom is stable if the forces among the particles that makeup the nucleus are balanced. An atom is unstable (radioactive) if these forces are unbalanced; if the nucleus has an excess of internal energy. Instability of an atom's nucleus may result from an excess of either neutrons or protons.
The stability of atoms depends on whether or not their outer-most shell is filled with electrons. If the outer shell is filled, the atom is stable. Atoms with unfilled outer shells are unstable, and will usually form chemical bonds with other atoms to achieve stability.
When the atoms of an element have extra neutrons or protons it creates extra energy in the nucleus and causes the atom to become unbalanced or unstable. Whether radioactive elements can become stable and if so, how. The unstable nucleus of radioactive atoms emit radiation.
Stable isotopes
It is the number of neutrons in the nucleus of the atom that guarantees this stability. Let's go back to the case of carbon-12, which is stable. It has 6 protons and 6 neutrons. As for carbon-14, it has 6 neutrons and 8 neutrons, which creates its instability.
Radioactive isotopes are unstable because they have too many electrons. Many elements have one or more isotopes that are radioactive. These isotopes are called radioisotopes. An example of a radioisotope is carbon-14.
Elements with atomic number (Z) greater than 82 have no stable isotopes. Isotopes of elements with atomic number (Z) less than 20 and with a neutron to proton ratio of close to 1 are more likely to be stable if the nucleus contains an even number of protons and an even number of neutrons.
On the periodic table, most elements have at least one stable form. But others have only unstable forms, all of which decay by emitting radiation and transforming into different elements until becoming one that's stable.
For example, uranium-238 is unstable because it spontaneously decays over time, but if a sample of uranium-238 is allowed to sit for 1000 years, only 0.0000155% of the sample will have decayed. However, other unstable nuclei, such as berkelium-243, will be almost completely gone (>99.9999% decayed) in less than a day.
There are two main types of isotopes: stable and unstable (radioactive). There are 254 known stable isotopes. All artificial (lab-made) isotopes are unstable and therefore radioactive; scientists call them radioisotopes. Some elements can only exist in an unstable form (for example, uranium).
A stable atom is an atom that has enough binding energy to hold the nucleus together permanently. An unstable atom does not have enough binding energy to hold the nucleus together permanently and is called a radioactive atom.
Protons—whether inside atoms or drifting free in space—appear to be remarkably stable. We've never seen one decay. However, nothing essential in physics forbids a proton from decaying. In fact, a stable proton would be exceptional in the world of particle physics, and several theories demand that protons decay.
Hence, oxygen is not a stable element.
Answer and Explanation: The elements with no stable isotopes are technetium, promethium, and all elements with atomic numbers 83 or greater.
Hence, the most unstable particle is the neutron with a half-life of only 106 minutes. The phenomenon of the disintegration of radioactive elements with the emission of alpha, and beta particles, and the formation of atoms of new elements.
Heavier nuclei are less stable—that's something we all learned in school. Adding more nucleons (protons and neutrons) makes atoms more likely to break apart. It's one reason why elements heavier than plutonium haven't been found in nature.
Elements beyond uranium should become more and more unstable as they get heavier, as Coulomb repulsion starts to be stronger than the strong force that holds the nucleus together.
The most common isotope of iron, iron-56, is thought to be the most stable nucleus since it has the lowest mass per nucleon of all nuclides. Iron-56 is also a strongly and effectively bound nucleus, having a binding energy of. 8 MeV per nucleon.
But one oxygen atom cant exist on its own, because its unstable. Usually any atom needs 8 electrons in its outer orbit in order to stay stable. But, the Oxygen atom has 6 electrons in its outer orbit. So, it needs two more electrons in order to make it 8.
The arrangement of particles within uranium-235 is somewhat unstable and the nucleus can disintegrate if it is excited by an outside source. When a U-235 nucleus absorbs an extra neutron, it quickly breaks into two parts. This process is known as fission (see diagram below).
An isotope is an atom that has different numbers of neutrons and protons. Isotopes can be lighter or heavier, depending on the excess or lack of neutrons. Most isotopes do not occur in nature because they are unstable. Isotopes that do occur in nature are said to be stable.
The least stable ground state isotope is francium-215, with a half-life of 0.12 μs: it undergoes a 9.54 MeV alpha decay to astatine-211.
Because carbon-14 has six protons, it is still carbon, but the two extra neutrons make the nucleus unstable. In order to reach a more stable state, carbon-14 releases a negatively charged particle from its nucleus that turns one of the neutrons into a proton.
Unstable isotopes (which are thus radioactive) are called radioisotopes. Some elements, eg uranium, have no stable isotopes. When an atom of a radioisotope decays, it gives off some of its excess energy as radiation in the form of gamma rays or fast-moving sub-atomic particles.