effective nuclear charge

(noun)

That experienced by an electron in a multi-electron atom, typically less for electrons that are shielded by core electrons.

Related Terms

Examples of effective nuclear charge in the following topics:

  • 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.
    • As an approximation, we can estimate the effective nuclear charge on each electron.
    • The effective nuclear charge on an electron is given by the following equation:
    • What is the effective nuclear charge for each?
    • Diagram of the concept of effective nuclear charge based on electron shielding.

  • Multielectron Atoms

    • The size of the shielding effect is difficult to calculate precisely due to effects from quantum mechanics.
    • As an approximation, the effective nuclear charge on each electron can be estimated by: Zeff=Z−σZ_\text{eff} = Z - \sigma, where $Z$ is the number of protons in the nucleus and σ\sigma is the average number of electrons between the nucleus and the electron in question. σ\sigma can be found by using quantum chemistry and the Schrodinger equation or by using Slater's empirical formula.
    • Each has 10 electrons, and the number of nonvalence electrons is two (10 total electrons minus eight valence electrons), but the effective nuclear charge varies because each has a different number of protons:
    • As a consequence, the sodium cation has the largest effective nuclear charge and, therefore, the smallest atomic radius.
    • A multielectron atom with inner electrons shielding outside electrons from the positively charged nucleus

  • Nuclear Fission

    • Most fissions are binary fissions that produce two charged fragments.
    • Occasionally, about 2 to 4 times per 1000 events, three positively charged fragments are produced, which indicates a ternary fission.
    • The strong nuclear force is the force between two or more nucleons.
    • The electromagnetic force causes the repulsion between like-charged protons.
    • These two forces produce opposite effects in the nucleus.

  • Nuclear Size and Density

    • Nuclear size is defined by nuclear radius; nuclear density can be calculated from nuclear size.
    • Nuclear size is defined by nuclear radius, also called rms charge radius.
    • It can be measured by the scattering of electrons by the nucleus and also inferred from the effects of finite nuclear size on electron energy levels as measured in atomic spectra.
    • The first estimate of a nuclear charge radius was made by Hans Geiger and Ernest Marsden in 1909, under the direction of Ernest Rutherford at the Physical Laboratories of the University of Manchester, UK.
    • This gives a charge radius for the gold nucleus ($A=197$) of about 7.5 fm.

  • Binding Energy and Nuclear Forces

    • Binding energy is the energy used in nuclear power plants and nuclear weapons.
    • The nuclear force is now understood as a residual effect of an even more powerful "strong force" or strong interaction.
    • Gluons hold quarks together with a force like that of an electric charge (but of far greater power).
    • Such forces between atoms are much weaker than the attractive electrical forces that hold together the atoms themselves (i.e., that bind electrons to the nucleus), and their range between atoms is shorter because they arise from a small separation of charges inside the neutral atom.
    • These nuclear forces are very weak compared to direct gluon forces ("color forces" or "strong forces") inside nucleons, and the nuclear forces extend over only a few nuclear diameters, falling exponentially with distance.

  • Nuclear Fusion

    • The protons are positively charged and repel each other, but they nonetheless stick together, demonstrating the existence of another force referred to as nuclear attraction.
    • This force, called the strong nuclear force, overcomes electric repulsion in a very close range.
    • The effect of nuclear force is not observed outside the nucleus, hence the force has a strong dependence on distance; it a short-range force.
    • At large distances, two nuclei repel one another because of the repulsive electrostatic force between their positively charged protons.
    • 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.

  • The Compton Effect

    • The Compton Effect is the phenomenon of the decrease in energy of photon when scattered by a free charged particle.
    • Compton scattering is an inelastic scattering of a photon by a free charged particle (usually an electron).
    • Inverse Compton scattering also exists, and happens when a charged particle transfers part of its energy to a photon.
    • Although nuclear Compton scattering exists, Compton scattering usually refers to the interaction involving only the electrons of an atom.
    • Studying this effect, Compton verified that photons have momentum.

  • Nuclear Weapons

    • The proliferation of nuclear weapons, explosive devices which derive force from nuclear reactions, is a key challenge of foreign policy.
    • The proliferation of nuclear weapons, explosive devices which derive their destructive force from nuclear reactions (either fission or a combination of fission and fusion), is an important challenge of foreign policy.
    • By the 1960s, steps were being taken to limit both the proliferation of nuclear weapons to other countries and the environmental effects of nuclear testing.
    • The Partial Test Ban Treaty (1963) restricted all nuclear testing to underground facilities, to prevent contamination from nuclear fallout, while the Nuclear Non-Proliferation Treaty (1968) attempted to place restrictions on the types of activities signatories could participate in, with the goal of allowing the transference of non-military nuclear technology to member countries without fear of proliferation.
    • Identify the history of nuclear weapons and international efforts to regulate them

  • Charge Distribution in Molecules

    • Similarly, nitromethane has a positive-charged nitrogen and a negative-charged oxygen, the total molecular charge again being zero.
    • Finally, azide anion has two negative-charged nitrogens and one positive-charged nitrogen, the total charge being minus one.
    • Because of their differing nuclear charges, and as a result of shielding by inner electron shells, the different atoms of the periodic table have different affinities for nearby electrons.
    • Electronegativity differences may be transmitted through connecting covalent bonds by an inductive effect.
    • Excellent physical evidence for the inductive effect is found in the influence of electronegative atoms on the nmr chemical shifts of nearby hydrogen atoms.

  • Fusion Reactors

    • Fusion power is the power generated by nuclear fusion processes.
    • Fusion between the nuclei is opposed by the repulsive positive electrical charge common to all nuclei because they contain protons.
    • The easiest way to do this is to heat the atoms, which has the side effect of stripping their electrons and leaving them as bare nuclei.
    • The temperatures required to provide the nuclei with enough energy to overcome their repulsion is a function of the total charge.
    • Therefore, hydrogen, which has the smallest nuclear charge, fuses at the lowest temperature, and is often used as fuel.