LEVEL – I
1. The atomic number of an element is 5 and mass number is 11. Find the number of electrons, protons and neutrons present in an atom of it. How can this element be represented?
Ans : Number of electrons (Z=5)=5
Number of protons (Z=5)=5
Number of neutrons (A=Z)=11-5=6
Since the atomic number is 5 , the element is boron and is represented as : 5B11
2. The Kinetic energy of an electron is 4.55 X 10-25 J. The mass of electron is 9.1X10-31 kg. Calculate velocity, momentum and the wavelength of the electron.
Ans : Setp-1 Calculation of the velocity of electron.
Kinetic energy = ½ mv2 = 4.55 X 10-25 J = 4.55 X 10-25 kg m2 s-2
3. Which has higher energy, 3d or 4s? Explain?
Ans: 3d because n+l for 3d is 3+2=5, but for 4s it is 4+0=5
4. State and explain Hund’s rule of maximum multiplicity?
Ans : It states that pairing of e in the degenerate orbital is not possible until there is one e in each orbital
5. Define (i) work function (ii) Threshold frequency.
Ans: (i) Work function is the minimum energy of light radiations required to remove an electron from the metal surface. (ii) Frequency related to work function is threshold frequency.
6. Half filled and full filled orbitals have extra stability. Why?
Ans: Due to exchange energy
7. What are isoelectronic series?
Ans : Species having same no of electrons.
LEVEL – 2
1. The uncertainty in the position of a moving bullet of mass 10g is 10-5m.Calculate the uncertainty in the velocity.
Ans: Uncertainty Principle
3. Which of the following are iso-electronic species?
Na+,, K+, Mg2+, Ca2+, S2-, Ar.
Ans: Na+ and Mg2+ are iso- electrons species (have 10 electrons) K+, Ca2+, S2- are iso-electronic species (have 18 electrons).
4. (i) Write the electronic configuration of the following ions? (a) H- (b) Na+ (c) O2- (d) F-.
(ii) What are the atomic numbers of the elements whose outermost electronic configurations are represented by:
(a) 3s1 (b) 2p3 and (c) 3d6 ?
(iii) Which atoms are indicated by the following configurations? (a) [He] 2s1 (b) [Ne] 3s2 3p3 (c) [Ar] 4s2 3d1.
Ans: (i) (a) 1s2 (b) 1s2 2s2 2p6 (c) 1s2 2s22p6. (d) 1s2 2s22p6.
(ii) (a) Na (Z=11) has outermost electronic Configuration = 3s1
(b) N (Z=7) has outermost electronic Configuration = 2p3
(c) Fe (Z=26) has outermost electronic Configuration = 3d6
(iii) (a) Li (b) P (c) Sc
5. Show that the circumference of Bohr orbit for the hydrogen atom is an integral multiple of the de Broglie wavelength associated with the electron revolving around the orbit.
Ans: According to Bohr’s theory,
6. The unpaired electrons in Al and Si are present in 3p orbital. Which electrons will experience more effective nuclear charge from the nucleus?
Ans: Configuration of the two elements are:
Al (Z=13) : [Ne]103s23p1 ; Si (Z=14) :[Ne]103s23p2
The unpaired electrons in silicon (Si) will experience more effective nuclear charge because the atomic number of the element Si is more than that of Al.
7. The electronic energy is negative. How will you account for that?
Ans: Electron just out of atom has zero energy. It enters in the atom due to attraction of atom so it loses energy.
8. How many unpaired electrons are present in Pd (Z=46)?
Ans: Zero
9. Write electronic configuration of Ca(z=24) and Cu(z=22).
Ans: Ca= 1s2 2s2 2p6 3s2 3p6 4s2
Cu=1s2 2s2 2p6 3s2 3p6 3d10 4s1
LEVEL – 3
4. Draw the shape of all d orbitals.
Ans:
5. Consider an element Z that has two naturally occurring isotopes with the following percent abundances: the isotope with a mass number of 19.0 is 55.0% abundant; the isotope with a mass number of 21.0 is 45.0% abundant. Calculate the average ATOMIC MASS for element Z.
6. Complete the following table.
