This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “General Properties of the Transition Elements (D-Block)”.
1. The d-electrons affect the properties of the transition elements to a great extent.
Explanation: The transition elements differ from one another only in the number of electrons in the d-orbitals of the penultimate shell. The d-orbitals of the transition elements project to the periphery of the atom more than s and p-orbitals. Therefore, the d-electrons affect the properties of transition elements to a great extent.
2. Why is there an increase in the atomic radius of transition elements at the end of the period?
a) Increased electron-electron repulsions
b) Decreased electron-electron repulsions
c) Increase in nuclear charge
d) Increase in atomic mass
Explanation: Near the end of the period, the increased electron-electron repulsions between added electrons in the same orbitals are greater than the attractive forces due to increased nuclear charge. This results in the expansion of the electron cloud and therefore, increases the atomic size.
3.Which of the following iswhy the atomic radii of the second and third transition series are almost same?
a) Actinoid contraction
b) Radioactive nature
c) Lanthanoid contraction
d) Filled d-orbital
Explanation: In the atoms of the second transition series, the number of shells increases and so, their atomic radii is greater than that of the first transition series. The atomic radii of the second and third transition series are almost same due to lanthanoid contraction.
4. The decrease in atomic size of the d-block elements in a series is small after midway.
Explanation: In the beginning of the series, the atomic radius decreases with increase in atomic number as the nuclear charge increases and the shielding effect of the d-electrons is small. After midway, the increased number of d-electrons show an increase in shielding effect which counterbalances the increase in nuclear charge. Therefore, the decrease in atomic radius post midway is minimal.
5. Which of the following is not a property of a transition metal?
a) They are lustrous
b) They are malleable
c) They are ductile
d) They have low boiling points
Explanation: The transition metals exhibit all the characteristics of metals. They are hard, lustrous, malleable and ductile, have high melting and boiling points, high thermal and electrical conductivity and high tensile strength.
6. What type of bond do the transition elements form with themselves?
a) Ionic bond
b) Covalent bond
c) Coordinate bond
d) Metallic bond
Explanation: Transition elements have relatively low ionization energies and have one or two electrons in their outermost energy level. As a result, they form metallic bonds. This is also the reason behind the metallic properties of transition elements.
7. Which of the following is not a very hard metal?
Explanation: Greater the number of unpaired electrons, stronger is the bonding due to overlapping of unpaired electrons between different metal atoms. Cr, Mo and W have maximum unpaired d-electrons and are harder metals whereas Zn, Cd and Hg are not very hard due to the absence of unpaired electrons.
8. Which of the following statements is incorrect?
a) Manganese has an abnormally low boiling point
b) Transition elements have low enthalpies of atomisation
c) Transition elements exhibit metallic bonding
d) Transition metals generally have a high boiling point
Explanation: Transition metals generally have high melting and boiling points. Magnesium and technetium have abnormally low boiling points. This is due to the strong metallic bonds between the atoms. They have high enthalpies of atomization.
9. Which of the following element has the highest density among transition metals?
Explanation: Among the d-block elements, iridium has the highest density (22.61 g cm-3) whereas scandium has the lowest density (3.43 g cm-3). Osmium has slightly lesser density (22.59 g cm-3) than iridium.
10. Which of the following element has the highest ionisation enthalpy?
Explanation: Ionisation enthalpy shows only a little variation on moving along the period of d-block elements. The first ionisation enthalpy of zinc, cadmium and mercury are higher than the other elements in their respective periods because of the fully filled (n-1)d10ns2 configuration.
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