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Questions and Answers
What is the relationship between effective nuclear charge (Zeff) and the actual nuclear charge (Z)?
What is the relationship between effective nuclear charge (Zeff) and the actual nuclear charge (Z)?
- Zeff equals Z when there are no inner electrons.
- Zeff is always greater than Z.
- Zeff and Z are identical in many-electron atoms.
- Zeff is less than Z due to screening effects. (correct)
Which factor contributes to the decrease in effective nuclear charge experienced by outer electrons?
Which factor contributes to the decrease in effective nuclear charge experienced by outer electrons?
- Absence of inner electrons.
- Greater distance of the outer electron from the nucleus. (correct)
- Decrease in the number of protons in the nucleus.
- Increase in electron affinity of the atom.
What does the screening constant (S) represent in the equation Zeff = Z - S?
What does the screening constant (S) represent in the equation Zeff = Z - S?
- The total positive charge in the nucleus.
- The number of valence electrons in an atom.
- The average distance between the outer electron and the nucleus.
- The extent of electron-electron repulsion affecting outer electrons. (correct)
According to Coulomb's law, what increases the attractive force between an electron and the nucleus?
According to Coulomb's law, what increases the attractive force between an electron and the nucleus?
How does the presence of inner electrons affect outer electrons in a many-electron atom?
How does the presence of inner electrons affect outer electrons in a many-electron atom?
What is the primary reason effective nuclear charge (Zeff) is less than actual nuclear charge (Z)?
What is the primary reason effective nuclear charge (Zeff) is less than actual nuclear charge (Z)?
Which statement best describes the concept of effective nuclear charge?
Which statement best describes the concept of effective nuclear charge?
When calculating effective nuclear charge, which of the following cannot be changed to increase Zeff?
When calculating effective nuclear charge, which of the following cannot be changed to increase Zeff?
What is represented by the variable S in the context of inner electrons?
What is represented by the variable S in the context of inner electrons?
What is the primary effect of shielding on the attractive force between the nucleus and valence electrons?
What is the primary effect of shielding on the attractive force between the nucleus and valence electrons?
Given sodium's electron configuration [Ne]3s1, what is the expected effective nuclear charge (Zeff) for the 3s electron?
Given sodium's electron configuration [Ne]3s1, what is the expected effective nuclear charge (Zeff) for the 3s electron?
What causes an increase in effective nuclear charge (Zeff) for the 3s electron in sodium beyond the expected model?
What causes an increase in effective nuclear charge (Zeff) for the 3s electron in sodium beyond the expected model?
How does the energy of orbitals with the same n value change with increasing l value in a multi-electron atom?
How does the energy of orbitals with the same n value change with increasing l value in a multi-electron atom?
Which of the following best explains why core electrons are most effective at shielding valence electrons?
Which of the following best explains why core electrons are most effective at shielding valence electrons?
What is the result of the repulsive effect among electrons in an atom?
What is the result of the repulsive effect among electrons in an atom?
In a sodium atom, how would the effective nuclear charge (Zeff) for the 3s electron change if its probability of being closer to the nucleus was eliminated?
In a sodium atom, how would the effective nuclear charge (Zeff) for the 3s electron change if its probability of being closer to the nucleus was eliminated?
What is the relationship between the 2s and 2p orbital energies in many-electron atoms?
What is the relationship between the 2s and 2p orbital energies in many-electron atoms?
How does the effective nuclear charge (Zeff) change across a period in the periodic table?
How does the effective nuclear charge (Zeff) change across a period in the periodic table?
What is the approximate Zeff experienced by the 2s electron in beryllium (Be)?
What is the approximate Zeff experienced by the 2s electron in beryllium (Be)?
What factor primarily contributes to the increase in Zeff as you move down a column in the periodic table?
What factor primarily contributes to the increase in Zeff as you move down a column in the periodic table?
What is the value of Zeff for the valence electrons in sodium (Na)?
What is the value of Zeff for the valence electrons in sodium (Na)?
What is the formula to estimate the effective nuclear charge (Zeff)?
What is the formula to estimate the effective nuclear charge (Zeff)?
Which of the following statements about core electrons is true?
Which of the following statements about core electrons is true?
In which situation would the effective nuclear charge (Zeff) be highest?
In which situation would the effective nuclear charge (Zeff) be highest?
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Study Notes
Effective Nuclear Charge (Zeff)
- Effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom, influenced by both nuclear charge and electron shielding.
- The attractive force between an electron and the nucleus is determined by the strength of nuclear charge and the distance from the nucleus.
- Coulomb’s law explains that greater nuclear charge increases attraction, while increased distance decreases it.
Electron Interactions
- In multi-electron atoms, electrons experience both attraction to the nucleus and repulsion from other electrons.
- It’s difficult to precisely calculate these interactions due to complex electron-electron repulsions.
- Instead, the effective nuclear charge is treated as a single positive charge at the nucleus, modified by the presence of other electrons.
Screening Effect
- Inner electrons provide a screening effect, reducing the attraction experienced by outer (valence) electrons.
- Screening constant (S) is used to quantify the amount of nuclear charge that is shielded from valence electrons.
- Zeff is calculated using the formula: Zeff = Z - S, where Z is the actual nuclear charge.
Example: Sodium Atom (Na)
- Sodium has an electron configuration of [Ne]3s1, with a nuclear charge of +11 and 10 core electrons.
- The expected screening constant (S) for sodium is 10, leading to an initial Zeff of 1+.
- Due to the 3s electron’s proximity to the nucleus, the effective nuclear charge is increased to approximately 3+.
Orbital Energy Levels
- The concept of Zeff explains energy differences in orbitals; in general, energies increase with increasing l value when n (principal quantum number) is constant.
- For example, in carbon (1s² 2s² 2p²), the 2s orbital is lower in energy than the 2p orbital due to stronger nuclear attraction.
Trends in Effective Nuclear Charge
- Effective nuclear charge increases across a period in the periodic table due to increased nuclear charge (more protons) with constant core electrons.
- Valence electrons become less effective at screening each other as nuclear charge increases, resulting in higher Zeff values.
- For lithium (Li), Zeff is around 1+, while for beryllium (Be), it is about 2+ due to less effective screening from core electrons.
Vertical Trends in Effective Nuclear Charge
- Across columns of the periodic table, Zeff does not change significantly; however, it generally increases slightly down a group due to less effective screening from more diffuse core electron clouds.
- For alkali metals, Zeff values increase from lithium (1.3+) to sodium (2.5+) to potassium (3.5+), despite similar core electron configurations.
Conclusion
- The formula Zeff = Z - S serves as an estimate; actual values of Zeff may vary but provide insight into an atom's structure and behaviors.
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