LESSON 2- ENC and Shielding Effect

Question 1

Shielding Electrons

Answer 1

The electrons in the energy levels between the nucleus and the valence electrons

Question 2

Why are they specifically called shielding

Answer 2

because they “shield” the valence electrons from the force of attraction exerted by the positively charged nucleus.

-This is why valence electrons require less energy to remove than the inner electrons

Question 3

Example of shielding e with fluorine

Answer 3

In fluorine there are 9 protons in the nucleus and there are 2 shielding electrons in the first energy level between the nucleus and the outer shell

Question 4

Trend of shielding e within a period

Answer 4

The # of shielding electrons stays the same within a period (except for increasing gradually and erratically across transition metals)

Question 5

Trend of shielding e with groups

Answer 5

Shielding electrons follow a pattern somewhat like the number of energy levels
They increase in steps as you go down a group

Question 6

Effective Nuclear Charge (Zeff)

Answer 6

The charge felt by the valence electrons after you have taken into account the number of shielding electrons that surround the nucleus.

Question 7

How to figure out ENC?

Answer 7

ENC = nuclear charge - # of shielding electrons
ENC (Zeff) = NC - SE

Question 8

Trend of ENC left to right in a period

Answer 8

The number of protons increase, but the number of shielding electrons stays the same, thus the effective nuclear charge felt by the valence electrons increases

Question 9

Top-to-bottom in a group with ENC

Answer 9

As you go down a group, the increase in the nuclear charge is cancelled out by the increase in shielding electrons and the effective nuclear charge stays the same