Evaluate Yourself: Chemistry Periodic Classification of Elements

Evaluate Yourself

1. What is the basic difference in approach between Mendeleev's periodic table and modern periodic table ?

2. The element with atomic number 120 has not been discovered so far. What would be the IUPAC name and the symbol for this element? Predict the possible electronic configuration of this element.

Answers:

Atomic number : 120

IUPAC temporary symbol : Unbinilium

IUPAC temporary symbol : Ubn                                                                   

Possible electronic configuration :[Og] 8s²

3. Predict the position of the element in periodic table satisfying the electronic configuration (n-1)d², ns2 where n=5

Answers:

Electronic Configuration : (n – 1)d² ns²

for n = 5, the electronic configuration is,

1s²2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 4d²

5s²Atomic number : 40

4^th group 5^th period (d block element)

= Zirconium

4. Using Slater's rule calculate the effective nuclear charge on a 3p electron in aluminium and chlorine. Explain how these results relate to the atomic radii of the two atoms.

Answers:

Electronic Configuration of Aluminium

Effective nuclear charge = Z – S

= 13 – 9.5

(Z_eff)_Al   = 3.5

Electronic Configuration of chlorine

5. A student reported the ionic radii of isoelectronic species X³⁺, Y²⁺ and Z^- as 136 pm, 64 pm and 49 pm respectively. Is that order correct? Comment.

Answers:

X³⁺, Y²⁺, Z^– are isoelectronic.

Effective  nuclear  charge  is  in the order  (Z_eff )_Z-  < (Z_eff )_Y2 +  < (Z_eff )_X3+ and

Hence, ionic radii should be in the order

r_Z -  > r_Y2 +  > r_X3+

The correct values are,

6. The first ionisation energy (IE₁) and second ionisation energy (IE₂) of elements X, Y and Z are given below.

Element   :  IE₁ (kJ mol^-1) : IE2 (kJ mol^-1)

X :  2370 :  5250

Y  : 522 :  7298

Z :  1680  : 3381

Which one of the above elements is the most reactive metal, the least reactive metal and a noble gas?

Answers:

Noble gases : Ioniation energy ranging from 2372 KJmol^–1 to 1037 kJ mol^–1.

For element X, the IE₁, value is in the range of noble gas, moreover for this element both IE₁ and IE ₂ are higher and hence X is the noble gas.

For Y, the first ionisation energy is low and second ionisation energy is very high and hence Y is most reactive metal.

For Z, both IE₁ and IE₂ are higher and hence it is least reactive.

7. The electron gain enthalpy of chlorine is 348 kJ mol^-1. How much energy in kJ is released when 17.5 g of chlorine is completely converted into Cl^- ions in the gaseous state?

Answers:

Cl(g) + e^– → Cl^–(g) ∆H = 348 kJ mol^–1 

For one mole (35.5g) 348 kJ is released.