Electron Shielding (8.1.2) Flashcards
• Every electron has a unique set of quantum numbers, and only two electrons fit in each orbital.
• Every electron has a unique set of quantum numbers, and only two electrons fit in each orbital.
• Electrons further from the nucleus feel a lower effective nuclear charge.
• Electrons further from the nucleus feel a lower effective nuclear charge.
• A 2s orbital is lower in energy than a 2p orbital for elements beyond hydrogen.
• A 2s orbital is lower in energy than a 2p orbital for elements beyond hydrogen.
By the Pauli exclusion principle, every electron
has a unique set of quantum numbers. For
example, the quantum numbers for one electron in
helium are 1, 0, 0, +1/2, while the quantum numbers
for the other electron in helium are 1, 0, 0, –1/2.
Only two electrons fit in each orbital. The only
difference between the two electrons in an orbital is
their electron spin.
Electrons further from the nucleus feel less of the
nuclear charge than electrons closer to the nucleus.
This is referred to as electron shielding. The
charge felt by a given electron is the effective
nuclear charge.
This is because the electrons closer to the nucleus
partially block the charge of the nucleus.
This is analogous to moths around a light bulb.
Moths further from the light bulb can be in the
shadow of moths closer to the light bulb, and
therefore see less of the light.
A 2s orbital is lower in energy than a 2p orbital for
elements beyond hydrogen.
This is because 2s orbitals have some electron
probability density closer to the nucleus than 1s
orbitals, while 2p orbitals have all of their electron
density outside of the 1s orbitals. This means that
2p orbitals are shielded by 1s and 2s orbitals. This
shielding causes 2p orbitals to feel a lower effective
nuclear charge, and therefore to be higher in
energy.
By the Pauli exclusion principle, every electron
has a unique set of quantum numbers. For
example, the quantum numbers for one electron in
helium are 1, 0, 0, +1/2, while the quantum numbers
for the other electron in helium are 1, 0, 0, –1/2.
Only two electrons fit in each orbital. The only
difference between the two electrons in an orbital is
their electron spin.
Electrons further from the nucleus feel less of the
nuclear charge than electrons closer to the nucleus.
This is referred to as electron shielding. The
charge felt by a given electron is the effective
nuclear charge.
This is because the electrons closer to the nucleus
partially block the charge of the nucleus.
This is analogous to moths around a light bulb.
Moths further from the light bulb can be in the
shadow of moths closer to the light bulb, and
therefore see less of the light.
A 2s orbital is lower in energy than a 2p orbital for
elements beyond hydrogen.
This is because 2s orbitals have some electron
probability density closer to the nucleus than 1s
orbitals, while 2p orbitals have all of their electron
density outside of the 1s orbitals. This means that
2p orbitals are shielded by 1s and 2s orbitals. This
shielding causes 2p orbitals to feel a lower effective
nuclear charge, and therefore to be higher in
energy.
Why is it that the 2s orbital is favored over the 2p orbital when a third electron is added?
Though their energies are very similar overall, the 2s orbital spends a little time inside the 1s orbital, thus achieving a slightly lower energy overall. (C)
The 2s electron is sometimes able to exist inside of the density of the 1s orbitals electron density, because of this the 2s orbital is a lower energy (and thus fills before) the 2p orbitals.
Which of the following orbitals is lowest in energy for a lithium atom?
2p (A)
The 2p orbitals are higher in energy than the 2s orbital in a lithium atom. However, they are the lowest in energy of the orbitals listed.
What is an effective nuclear charge?
The charge experienced by electrons in outer energy levels through electron shielding (B)
The electrons that are between the nucleus and the electron in question act to screen out some of the charge from the nucleus so the electron does not feel the full electrostatic attraction from the nucleus.
Why do 2s orbitals experience less shielding than 2p orbitals?
2s orbitals have some electron probability density closer to the nucleus than 1s orbitals. (C)
2s orbitals have a small amount of electron probability density inside of 1s orbitals, while 2p orbitals do not. Therefore, electrons in 2s orbitals can spend some time closer to the nucleus, and experience the full nuclear charge.
Why is it that the 2p orbitals do not decrease in energy as much as the 2s?
Because they experience a greater shielding effect (lower effective nuclear charge). (A)
Because the 2s orbital has the ability to partially exist inside the 1s orbital and feel a larger effective nuclear charge, the 2s orbital is able to be pulled to a lower energy level than the 2p which feels the full effect of the 1s electron shielding.
Which of the following would have the most negative energy?
An electron that is in a 2s orbital (D)
The most negative energy value that an electron can have is the one which is available to the electron in the lowest energy orbital. The 2s orbital is a slightly lower energy than the 2p orbital because of electron shielding.
If 2p orbitals had a small amount of electron probability density inside of the 1s orbital, how would electron shielding be affected?
The 2p orbitals would experience slightly less shielding than they do with their real probability clouds. (C)
Since electrons in 2p orbitals would be able to spend some time near the nucleus, they would experience less shielding than they do with their real probability clouds. However, it is impossible to tell from the information given how much of an effect this would have relative to 2s orbitals.
Which of the following is the best description of electron shielding?
Electron shielding is the decrease in the effective nuclear charge experienced by an electron in an outer energy level, due to the interaction of electrons at lower levels with the nucleus. (D)
Electron shielding causes the effective nuclear charge (the amount of pull experienced by an electron) to be decreased by an electron in an outer energy level. It is due to the influence of electrons at inner energy levels screening out some of the pull from the nucleus.
How many electrons can fit in any given orbital?
2 (B)
The two electrons in a given orbital have opposite spins.
The 2s and 2p orbitals are equal in energy in each of the following species except
B3+ (D)
B3+ still has two electrons. Therefore, the 2p orbital is shielded, and is higher in energy than the 2s orbital.
