nucleus

Examples of nucleus in the following topics:

• Nuclear Binding Energy and Mass Defect

  • A nucleus weighs less than its sum of nucleons, a quantity known as the mass defect, caused by release of energy when the nucleus formed.
  • This mass, known as the mass defect, is missing in the resulting nucleus and represents the energy released when the nucleus is formed.
  • As the size of the nucleus increases, the strong nuclear force is only felt between nucleons that are close together, while the coulombic repulsion continues to be felt throughout the nucleus; this leads to instability and hence the radioactivity and fissile nature of the heavier elements.
  • This graph shows the nuclear binding energy (in MeV) per nucleon as a function of the number of nucleons in the nucleus.
  • Notice that iron-56 has the most binding energy per nucleon, making it the most stable nucleus.

• Nuclear Fission

  • Within the nucleus, there are different forces that act between the particles.
  • This force binds protons and neutrons together inside the nucleus, and it is most powerful when the nucleus is small and the nucleons are close together.
  • These two forces produce opposite effects in the nucleus.
  • In these nuclei, it's possible for particles and energy to be ejected from the nucleus.
  • In order to initiate fission, a high-energy neutron is directed towards a nucleus, such as 235U.

• The Shielding Effect and Effective Nuclear Charge

  • The shielding effect, approximated by the effective nuclear charge, is due to inner electrons shielding valence electrons from the nucleus.
  • Electrons in an atom can shield each other from the pull of the nucleus.
  • Therefore, these electrons are not as strongly bound as electrons closer to the nucleus.
  • Because of shielding, the nucleus has less control over this 6s1 electron than it does over a 3s1 electron.
  • where Z is the number of protons in the nucleus (atomic number), and S is the number of electrons between the nucleus and the electron in question (the number of nonvalence electrons).

• Modes of Radioactive Decay

  • Radioactive decay occurs when an unstable atomic nucleus emits particles or light waves.
  • A nucleus with too many protons causes repulsion between these like charges.
  • To reduce this repulsion, the nucleus emits an α particle.
  • A nucleus with mass number A and atomic number Z is represented as (A, Z).
  • The column "Daughter nucleus" indicates the difference between the new nucleus and the original nucleus.

• Isotopes of Hydrogen

  • The nucleus of deuterium, called a deuteron, contains one proton and one neutron (mass number = 2), whereas the far more common hydrogen isotope, protium, has no neutrons in the nucleus.
  • 4H contains one proton and three neutrons in its nucleus.
  • The nucleus consists of a proton and four neutrons.
  • One tritium nucleus captures two neutrons from the other, becoming a nucleus with one proton and four neutrons.
  • The helium-8's neutrons were donated to the hydrogen's nucleus.

• Nuclear Fusion

  • Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse," to form a single heavier nucleus.
  • The nucleons in the interior of a nucleus have more neighboring nucleons than do those on the surface.
  • The binding energy per nucleon generally increases with the size of the nucleus but approaches a limiting value corresponding to that of a nucleus with a diameter of about four nucleons.
  • The electrostatic force, on the other hand, is dependent upon the inverse-square of the distance between two like-charged particles, so a proton added to a nucleus will feel an electrostatic repulsion from all the other protons in the nucleus.
  • At nucleus radii distances, the attractive nuclear force is stronger than the repulsive electrostatic force.

• Periods 1 through 3

  • The principle of valence emerged, attributable to the presence or absence of electrons and the energy of those electrons in the volume around an atom's nucleus.
  • Neils Bohr proposed a simplified picture of an atom, with a central nucleus surrounded by electrons in specific energy levels (n).
  • It is important to remember that the periodic table is a representation of atoms with zero net charge; they have as many electrons around the nucleus as they have protons in the nucleus.
  • In each full orbital, there are 2 electrons, giving a total of 10 to balance the positive charge provided by the 10 protons in the nucleus.
  • With the nucleus at the center with a positive charge, the electrons are "organized" in energy levels, or shells, at increasing distances from the nucleus.

• Ionization Energy

  • As the atomic radius decreases, it becomes harder to remove an electron that is closer to a more positively charged nucleus.
  • Conversely, as one progresses down a group on the periodic table, the ionization energy will likely decrease since the valence electrons are farther away from the nucleus and experience greater shielding.
  • They experience a weaker attraction to the positive charge of the nucleus.
  • This is because additional electrons in the same shell do not substantially contribute to shielding each other from the nucleus, however an increase in atomic number corresponds to an increase in the number of protons in the nucleus.
  • The ionization energy of the elements increases as one moves up a given group because the electrons are held in lower-energy orbitals, closer to the nucleus and thus more tightly bound (harder to remove).

• Average Atomic Mass

  • For example, the element hydrogen (the lightest element) will always have one proton in its nucleus.
  • The element helium will always have two protons in its nucleus.
  • Atoms of the same element can, however, have differing numbers of neutrons in their nucleus.
  • For any given isotope, the sum of the numbers of protons and neutrons in the nucleus is called the mass number.
  • The atomic number of chlorine is 17 (it has 17 protons in its nucleus).

• General Rules for Assigning Electrons to Atomic Orbitals

  • The central structure of an atom is the nucleus, which contains protons and neutrons.
  • This nucleus is surrounded by electrons.
  • Electrons with the lowest energy are found closest to the nucleus, where the attractive force of the positively charged nucleus is the greatest.
  • Here, electrons are arranged in energy levels, or shells, around the nucleus of an atom.
  • Electrons further away from the nucleus will have higher energy.