Effective Nuclear Charge vs Nuclear Charge
Atoms are mainly composed of protons, neutrons and electrons. Nucleus of the atom contains protons and neutrons. And there are electrons circling around the nucleus in orbitals. Atomic number of an element is the number of protons it has in the nucleus. The symbol for denoting the atomic number is Z. When the atom is neutral, it has the same number of electrons as protons. Thus, atomic number is equal to the number of electrons in this instance.
What is Nuclear Charge?
In a nucleus of an atom, mainly there are two sub atomic particles, neutrons and protons. Neutrons don’t have any electrical charge. But each proton has a positive charge. If there are only protons in the nuclei, the repulsion between those will be higher (like charges repel each other). Therefore, presence of neutrons is important to bind the protons together in the nuclei. The total positive charge of all the protons in a nucleus of an atom is known as the nuclear charge. Since the number of protons in an atom is similar to the atomic number, nuclear charge is also similar to the atomic number of the element. Therefore, the nuclear charge is unique to an element. And we can see how the nuclear charges are changing through the periods and groups of the periodic table. The nuclear charge increases from left to right through a period and it also increase down a group. Nuclear charge is important for an atom, because it is the electrostatic force that attracts and binds the orbital electrons to the nucleus. Since the electrons are negatively charged, they are attracted to the positive nucleus charges.
What is Effective Nuclear Charge?
Electrons in an atom are arranged in different orbitals. Inside a main orbital, there are other sub orbitals. For each sub orbital, two electrons are filled. The electrons in the last orbital are known as valence electrons, and they are situated farther from the nucleus. Since electrons are negatively charged, in an atom, there is electron – electron repulsion between them. And also there is electrostatic attraction between the protons in the nuclei and the orbital electrons. However, the nuclear charge doesn’t affect the same way to all the electrons. The electrons in the valence shells feel the minimum nuclear charge effect. This is because the electrons in between the nucleus, and the outer shells intervene and shield the nuclear charges. Effective nuclear charge is the nuclear charge experienced by the outer shell electrons. And this value is lower than the actual nuclear charge. For example, fluorine has nine electrons and nine protons. Its nuclear charge is +9. However, its effective nuclear charge is +7, because of the shielding due to two electrons. Effective nuclear charge of an atom can be calculated by the following formula.
Effective nuclear charge= atomic number- number of nonvalence electrons
What is the difference between nuclear charge and effective nuclear charge?
• Nuclear charge is the total positive charge of all the protons in a nucleus of an atom. Effective nuclear charge is the nuclear charge experienced by the outer shell electrons.
• Effective nuclear charge is lower than the value of nuclear charge. (Sometimes it can be similar)