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Mastering d- and f-block Elements (Class XII Chemistry)
Somak Chatterjee|Mar 8th, 2014 09:29pm
d-Block elements:
- General outer electronic configuration: (n -1)d1-10 ns1-2
- Generally known as: transition elements/ transition metals
|
S. No. |
Properties |
Trends |
Reason |
| 1 | Melting and boiling point | First transition series are lower than those of the heavier transition elements. | Occurrence of stronger metallic bonding (M-M bonding) in heavier metals |
| 2 | Atomic and ionic sizes | The atomic sizes of the elements of the first transition series are smaller than those of the corresponding heavier elements. | Increase in nuclear charge and number of electrons. |
| The atomic sizes of the elements in the third transition series are virtually the same as those of the corresponding members in the second transition series. | Lanthanoid contraction | ||
| 3 | Ionisation Enthalpies | The first ionisation enthalpies of the third transition series are higher than those of the first and second transition series. | Poor shielding effect of 4f electrons in the third transition series |
| 4 | Oxidation states | They show variable oxidation states. | Participation of ns and (n-1)d electrons in bonding |
| 5 | Chemical reactivity | Many of the transition metals are electropositive while few are noble. | Presence of empty d-orbitals (as they can accept electrons) |
| 6 | Magnetic properties | Some metals are paramagnetic while some are diamagnetic. It depends on number of electrons. | Magnetic moment increases with increase in number of electrons |
| 7 | Formation of Coloured Ions | All metals form coloured compounds. | d–d transition |
| 8 | Formation of Complex Compounds | Transition metals form a large number of complex compounds | Comparatively smaller size of metal ions, high ionic charges and availability of d-orbitals for bond formation |
| 9 | Catalytic Properties | Transition metals and their compounds are known for their catalytic activity | They can lend electrons or withdraw electrons from the reagent, depending on the nature of the reaction |
| 10 | Alloy Formation | Alloys are readily formed by these metals | Similar radii |
| 11 | Formation of Interstitial Compounds
|
They form interstitial compounds with hydrogen. | Hydrogen occupies interstitial sites in the metal lattice without changing the type of the lattice |
f-Block elements:
General outer electronic configuration: 4f1-146s2
Generally known as: inner transition elements
|
Properties |
Trends |
Reason |
| Atomic and ionic radii | There is a gradual decrease in atomic and ionic radii of Lanthanoids. | Lanthanoid contraction |
| Oxidation states | The lanthanoids exhibit mainly +3 oxidation state. |
Actinoid: These are the radioactive elements.
|
Properties |
Trends |
Reason |
| Atomic and ionic radii | There is a gradual decrease in atomic and ionic radii of actinoids . | Due to actinoid contraction |
| Oxidation states | There is a gradual decrease in atomic and ionic radii of actinoids. Exhibit mainly +3 oxidation state. | 5f, 6d, and 7s subshells are of comparable energies. |
| Ionisation enthalpy | Lower ionisation enthalpies | 5f electrons are less effectively shielded than 4f electrons. |
| Magnetic property | Paramagnetic | Presence of unpaired electrons. |
Lanthanoid Contraction: The steady decrease in the atomic and ionic radii of the transition metals as the atomic number increases is known as lanthanoid contraction. This is because of filling of 4f orbitals before the 5d orbitals. This contraction in size is quite regular.
Actinoid Contraction: The gradual decrease in the ionic radii with the increase in atomic no. is called actinoid contraction. It is due to the imperfect shielding of one 5f electron by the other in the same subshell.
Topics/ Questions that were asked previously
- Variable oxidation states of transition elements (2007, 2008)
- Atomic size of transition metals (2012)
Q. There is hardly any increase in atomic size with increasing atomic number in a series of transition metals? (2012 Set 3)
- Formation of coloured ions by transition metal ions (2007, 2010)
- Lanthanoid contraction (2007, 2008, 2009)
- Oxidation states of actinoids (2009, 2011, 2012 Set 3)
Q. Actinides exhibit a much larger number of oxidation states than the lanthanoids? (2012 Set 3)
Q. With the same d-orbital configuration (d4), Cr2+ is a reducing agent while Mn3+ is an oxidizing agent? (2012 Set 3)
NCERT questions which have been asked previously
|
Page |
Question Number |
Year |
|
211 |
Example 8.1 |
2010 |
|
220 |
Example 8.7 |
2010 |
|
220 |
Intext question 8.6 |
2010 |
|
232 |
Intext question 8.10 |
2009, 2008 |
|
234 |
Exercise-8.7 |
2007 |
|
– |
8.11 (ii) |
2008 |
|
– |
8.11 (iii) |
2007, 2010 |
|
– |
8.11 (iv) |
2008 |
|
– |
8.21 (i) |
2009, 2012 |
Best of luck,
Team Meritnation!
Add Comment 1 Comment
1. amaira | March 9th, 2014 at 4:26 pm
thanx for uploding this even ig=f im in 9th class i had learened al the periods excet the transiton series thank u for helping me wid it:)))
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