Main Difference – Nuclear Charge vs Effective Nuclear Charge
Nuclear charge and effective nuclear charge are two different chemical terms that are used to explain properties of atoms. Atoms are the smallest units that all matter is made out of. An atom is composed of a nucleus and electrons. The nucleus is composed of protons and neutrons. Protons are positively charged subatomic particles. These protons determine the nuclear charge of an atom. Electrons are in continuous movement around the nucleus. The pathways that electrons are moving are known as electron shells. The outermost electron shells have electrons with a minimum attraction to the nucleus. The nuclear attraction these electrons experience depends on the repulsion from inner shell electrons and the nuclear charge. The net charge an outer shell electron experiences is known as the effective nuclear charge. The main difference between nuclear charge and effective nuclear charge is that the value of effective nuclear charge is always a lower value than that of the nuclear charge.
Key Areas Covered
1. What is Nuclear Charge
– Definition, Explanation
2. What is Effective Nuclear Charge
– Definition, Explanation, Equation for Calculation
3. What is the Difference Between Nuclear Charge and Effective Nuclear Charge
– Comparison of Key Differences
Key Terms: Atom, Effective Nuclear Charge, Electrons, Electron Shells, Neutrons, Nuclear Charge, Protons, Subatomic Particles, Valence Electrons
What is Nuclear Charge
Nuclear charge is the total charge of the nucleus. It is essentially a positive charge. This is because the nucleus of an atom is composed of protons and protons are positively charged subatomic particles. Each and every atoms is composed of at least one proton in the nucleus. Thus, the nuclear charge is always a positive charge.
A nucleus is composed of protons and neutrons (except for protium isotope). Protons are positively charged, and neutrons are neutrally charged subatomic particles. One proton has +1 electrical charge. The number of protons increases across the periodic table of elements. Therefore the nuclear charge is also increased accordingly.
Figure 1: Deuterium atom is composed of a proton and a neutron in its nucleus. This single proton contributes to the nuclear charge of Deuterium.
Nuclear charge is the major reason for the attraction between nucleus and electrons. Since the nuclear charge is positive, negatively charged electrons are attracted to the nucleus due to electrostatic forces. The number of protons and electrons is equal in a neutral atom. In other words, electrons neutralize the nuclear charge.
Furthermore, the nuclear charge of an element is a fixed value. This means, even though there are isotopes in an element, the nuclear charge of all those isotopes is the same since isotopes have the same number of protons in their nuclei.
What is Effective Nuclear Charge
The effective nuclear charge is the net charge an electron experiences in an atom with multiple electrons. Outer shell electrons are the electrons located farthest from the nucleus. These electrons have the least attraction to the nucleus due to the distance. Therefore, these outer shell electrons have minimum effect from the nucleus. Electrons in the outermost shell are known as valence electrons.
In an atom with multiple electrons, there are electron-electron repulsion forces apart from electron-nucleus attraction force. The net charge experienced by an electron or the effective nuclear charge can be calculated using the following equation.
Equation of Effective Nuclear Charge
Zeff = Z – S
Where, Zeff is the effective nuclear charge,
Z is the atomic number (number of protons in the nucleus)
S is the number of shielding electrons.
Figure 02: Effective Nuclear Charge
Shielding electrons are the electrons located in between the nucleus and the outer shell electrons. The above equation shows the net charge obtained by deducting the repulsion by inner shell electrons from the attraction by the nucleus.
Difference Between Nuclear Charge and Effective Nuclear Charge
Definition
Nuclear Charge: Nuclear charge is the total charge of the nucleus.
Effective Nuclear Charge: Effective nuclear charge is the net charge that an outer shell electron experiences in an atom.
Electrons
Nuclear Charge: Nuclear charge does not depend on the charge of electrons in an atom.
Effective Nuclear Charge: Effective nuclear charge is calculated considering the effect of inner orbital electrons and the nuclear charge.
Protons
Nuclear Charge: Nuclear charge depends only on the number of protons present in the nucleus.
Effective Nuclear Charge: Effective nuclear charge does not depend only on the number of protons.
Value
Nuclear Charge: The value of nuclear charge is always a positive value and is higher than the value of effective nuclear charge.
Effective Nuclear Charge: Effective nuclear charge is a lower value than that of the nuclear charge.
Conclusion
Nuclear charge and effective nuclear charge are two different values that are calculated regarding atoms of chemical elements. Nuclear charge is the total charge of a nucleus. Effective nuclear charge is the net charge that an outermost shell electron experiences. The main difference between nuclear charge and effective nuclear charge is that the value of the effective nuclear charge is always a lower value than that of the nuclear charge.
References:
1. “Nuclear Charge.” Clackamas Community College, Available here.
2. Helmenstine, Anne Marie. “Effective Nuclear Charge Definition and Table.” ThoughtCo, Available here.
3. “Effective Nuclear Charge.” Chemistry LibreTexts, Libretexts, 14 Aug. 2016, Available here
Image Courtesy:
1. “Blausen 0527 Hydrogen-2 Deuterium” By BruceBlaus – Own work (CC BY 3.0) via Commons Wikimedia
2. “Effective Nuclear Charge” By Own work – Effective Nuclear Charge.gif (CC0) via Commons Wikimedia
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