Using the number of core electrons as the value for the she ding constant usuall

Question

Using the number of core electrons as the value for the she ding constant usually causes calculated values of Z_eff to be too large because: Select one: the number of core electrons does not account for all of the repulsions that can occur among electrons. there are attractions that will occur among valence and core electrons. valence e electrons feel mere effects from the nucleus than core electrons. the repulsions that occur among the valence electrons are mere important than the repulsions that occur among core electrons. there will be additional interactions that occur due to the neutrons n the nucleus.

Explanation / Answer

Question 1. What is the value of Zeff for a valence electron in an atom of aluminium?

Ans: Zeff means "Effective Nuclear Charge".

Calculation of Zeff:

a) Zeff = No. of protons (-) No. of Core electrons (or)

b) Zeff = Z-S (sigma);

where core electrons means those that are not part of the valence shell and as such, are not involved in bonding and S(sigma) means "Screening Constant" i.e., the no. of inner electrons screens the attraction in between the nucleus and the valence electrons.

Therefore Zeff of valence electrons in an atom of aluminium = No. of protons in Al (-) No. of core electrons

= 13 - 10 = +3

So, answer is +3.

Question 2: The shielding constant for a valence electron in a multi electron atom is approximately equal to:

Ans:Shielding constant means the no. of electrons that screens the attraction in between nucleus and the valence electrons. Hence, shielding constant is for a valence electron in a multi electron atom is equal to "the No. of Core electrons".

Hence the answer is "B".

Question 3: Which of the following questions could not be used to determine the effective nuclear charge?

Ans:

For Calculation of Zeff the following equations are used:

a) Zeff = No. of protons (-) No. of Core electrons (or)

b) Zeff = Z-S (sigma);

Therefore Zeff = attractions - repulsions are not used to determine the effective nuclear charge.

So, answer is "A"

Question 4: Using the number of core electrons as the value for the shielding constnat usually causes calculated values of Zeff to be too large because:

Ans: the number of core electrons does not account for all the repulsions that can occur among electrons.

So the answer is "A".

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