8.1.2 Electron Shielding

Question 1

Electron Shielding

Answer 1

• 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.
• A 2s orbital is lower in energy than a 2p orbital for elements beyond hydrogen.

Question 2

NOTE

Answer 2

• 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 shielding is because the electrons closer to the nucleus partially block the charge of the nucleus.
• Electron shielding 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 difference 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 difference in probability density distribution 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.

Question 3

Why is it that the 2p orbitals do not decrease in energy as much as the 2s?

Answer 3

Because they experience a greater shielding effect (lower effective nuclear charge).

Question 4

Why is it that the 2s orbital is favored over the 2p orbital when a third electron is added?

Answer 4

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

Question 5

The 2s and 2p orbitals are equal in energy in each of the following species except

Answer 5

B3+

Question 6

How many electrons can fit in any given orbital?

Answer 6

2

Question 7

What is an effective nuclear charge?

Answer 7

The charge experienced by electrons in outer energy levels through electron shielding

Question 8

Which of the following orbitals is lowest in energy for a lithium atom?

Answer 8

2p

Question 9

Which of the following would have the most negative energy?

Answer 9

An electron that is in a 2s orbital

Question 10

Which of the following is the best description of electron shielding?

Answer 10

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

Question 11

Why do 2s orbitals experience less shielding than 2p orbitals?

Answer 11

2s orbitals have some electron probability density closer to the nucleus than 1s orbitals

Question 12

If 2p orbitals had a small amount of electron probability density inside of the 1s orbital, how would electron shielding be affected?

Answer 12

The 2p orbitals would experience slightly less shielding than they do with their real probability clouds