Chemistry 1910 D-block elements: Metal properties
How can can use the trend in Zeff to explain the trend seen in ionization energies?
(1) For K to Ca, we see that the4s electrons has a higher Zeff relative to the 3d electrons and will be lower in energy -4s orbitals fill first. NO d electrons (2) For Sc the 4s and 3d electrons experience the same Zeff.Sc tends to lose both its 3d1 and 4s2 electrons to form Sc3+ ions. (3) The lower Zeff , for the 4s electrons from Ti - Zn indicates that the 4s orbitals are higher in energy than the 3d orbitals and these electrons are easily lost to form 2+ ions.
State the trends in ionization energies of 1st row d-block elements.
(1) From scandium to zinc a small change in the values of the first and second ionization energies is observed: this is due to the build-up of electrons in the immediately underlying d-sub-shells that efficiently shields the 4s electrons from the nucleus and minimizing the increase in effective nuclear charge from element to element. (2) The increases in third and fourth ionization energy values are more rapid. The increase in the 3rd I.E. isn't smooth across the series and there is a decrease from Mn to Fe. The anomaly is related to the electronic configuration of of the M2+ and M3+ ions and the nature of the electron that is removed on ionization. Ionization of Fe2+ has an E.C. [Ar] 3d^6 thus ionization involves the loss of a paired electron. Mn2+ has the E.C. of [Ar] 3d^5 thus the loss of an unpaired electron occurs on ionization. Electron-electron repulsion is greater between paired electron in the same orbitals than between unpaired electrons in different orbitals. Ionization of Fe2+ reduces electron-electron repulsion. Additionally, removal of an electron from Mn2+ involves the reduction in the exchange energy as you reduce the amount of unpaired electrons.
Periodic trends of main group elements versus d-block elements.
(1) The chemistry of the main group elements changes dramatically across a given period as the number of valence electrons changes. Transition metals however show great similarities within a period because the chemistry of its electrons in the d orbitals do not readily participate in bonding as easily as s and p orbitals. (2) As we move from left to right of the main group elements the added electron does not efficiently shield the increasing nuclear charge, so nuclear charge felt by outer most electrons increases - radii becomes smaller. For the transition elements atomic radii remains relatively similar across the period. As we go across the period for 1st row d-block elements, electrons are added to the underlying d-subshells, efficiently shielding the 4s electrons from the nucleus and minimizing the increase in effective nuclear charge from element to element, hence, small variations in periodic properties.
What are the properties of d-block elements?
(1) They are ALL metals (2) Most form coloured compounds (3) They are good conductors of heat and electricity (4) They can be hammered or bent into shapes easily - malleable and ductile (5) They tend to be less reactive than s-block metals (6) They tend to have relatively high melting points (7) They are among the most useful of all elements - high oxidation states
What nine of the d-block elements are essential for life?
(1) V (2) Hg (3) Mo (4) Mn (5) Fe (6) Ni (7) Zn (8) Cr (9) Co
OXIDATION STATES BY 1ST ROW D-BLOCK ELEMENTS
(1)Towards the right of the period the most common oxidation state is +2 as the 3d orbitals become lower in energy as the nuclear charge increases. (2) For the first 5 elements ( Sc - Mn) the maximum oxidation state corresponds to losing all 4s and 3d electrons. (3) The high oxidation states found in Fe, Co, Ni, Cu, Zn. are rare and their compounds are very strong oxidizing agents. (4) Ti, V, Cr, Mn, Fe, Co, Ni, have low oxidation states which are not stable in aqueous solution but are stabilized by ligands such as CO.
What are the deviations in the first d-block row elements atomic radii? Account for these deviations.
- Decrease in atomic radii from Sc to Cr - Mn has anomalously high atomic radii - Fe, Co, Ni are very similar in atomic radii - Ni to Zn are slight increase The deviation from the trend in atomic radii is caused by electron-electron repulsions. For the elements on the right-hand side of the series, as more electrons are placed in the d orbitals there is an increase in electron-electron repulsion which is more significant than the increase in effective nuclear charge or Zeff, causing atomic radius to increase. The trend in the difference in atomic radius is relatively small compared to main group elements.
Most first d-block elements have an electronic configuration (E.C.) of 3d^n 4s^2. Exceptions to this are?
1. Chromium whose E.C. is 3d^5 4s^1 2. Copper whose E.C. is 3d^5 4s^1
What are the importance of transition elements?
1. Therapeutic drugs 2. Chemical sensors 3. Coloring agents - paints, pigments, cosmetics 4. Biological molecules - haemoglobin, chlorophyll, catalysts 5. Gems (Jewelry and technological applications) - rubies, emeralds, garnets, etc. lasers 6. Construction materials
Work out the E.C. of Co ^3+ and Co^0. Show all working and explanatory steps.
1. Write down the E.C. of Co atom and place all electrons in the d orbital. Co atomic number is 27 i.e. [Ar] 3d^7 4s^2 --> [Ar] 3d^9 Co^3+ lost electrons hence, [Ar] 3d^6 is E.C. Co^0 is neutral hence, [Ar] 3d^9 is E.C.
For oxidation states LOWER THAN +2, the 4s electrons must be transferred into _____ orbitals before removing electrons when finding out the electronic configuration unless the d orbitals are full.
3d orbitals
The orbital in the picture is a ________?
Ans: dx^2 y^2
Name the d orbital in the picture.
Ans: dxy
What orbital is depicted in the picture?
Ans: dxz
Identify the d orbital in the diagram.
Ans: dyz
What d orbital is in the diagram?
Ans: dz^2
How does period number relate to the position of d-block elements?
Elements from period 4 are called first row d block elements, period 5, 6 and 7 are called second, third and fourth row d-block elements.
Why do first row d-block elements have the 4s orbitals filled even though it is higher in energy than 3d orbitals?
For a free atom of a first row d-block element, the 4s orbital is more diffused than the 3d orbitals, so putting electrons in this orbital reduces electron-electron repulsion.
What elements does the IUPAC definition of a transition element exclude? And why?
Group 12 elements - Zinc, Cadmium and Mercury because they only form ions with a d^10 configuration they are called d-block metals.
Does the size of the orbital increase or decrease in this order: 3d<4d<5d?
Increase
Which of the elements in the first row d-block elements has a variation in atomic orbital energies? What is the variation?
Manganese, Mn with an atomic number (Z) = 25. The 3d orbital is lower in energy than the 4s orbital.
Explain why is it easier to remove an electron from Fe2+ than Mn2+ even though the zeff of iron is higher.
Mn2+ requires a reduction in exchange energy which reduces the numbers of pairs of parallel electrons to remove an electron unlike the removal of an electron from Fe2+.
What is the IUPAC definition of a transition element?
One whose atom has partially filled/incompletely d-orbitals or that can give rise to cations with partially filled d orbitals.
Why is there a widespread occurrence of alloys for transition metals?
Since there is little difference in the atomic radii of most of the first row transition metals, it is relatively easy for one to substitute for another in a lattice.
What is the Lanthanide Contraction?
The effect that results from from poor shielding of nuclear charge force by 4f electrons; the 6s electrons are drawn towards the nucleus, thus resulting in a smaller atomic radius.
Ions and compounds of the d-block elements NEVER contain 4s electrons. Why is this so?
The electrons in the 4s orbitals are higher in energy than the electrons in the 3d orbitals thus the 4s electrons are lost first. When metal centers are involved in forming a molecule or compound, electron-electron repulsions are reduced - 4s orbitals are unoccupied.
The f-block metals lie between ______________ and ________ and also between ________ and ________.
The f-block metals lie between La and Hf and also Ac and Rf.
What is a triad?
The first three elements in a d-block group.
Relate zeff to first row d-block ionization energies.
The increasing effective nuclear charge across the first row d-block elements also affects their ionization energies, which increase from left to right.
The size of an atom/atomic radii of transition elements is highly dependent on what?
The size of an atom/atomic radii is dependent on the 4s orbitals. The pull of the increasing number of protons in the nucleus is offset by the extra screening due to the increasing number of 3d electrons. Thus, the transition elements atomic radii remains relatively similar across the period.
Why are scandium and zinc not usually classified as transition metals?
The transition metals are compounds that form at least 1 stable ion where the compound has an incomplete d subshell. Therefore, Scandium is not a transition metal, because it forms only Sc3+ ions with n d-electrons, and Zn is not a transition metal because it forms only Zn2+ ions with all the 3d electrons present.
Explain why the +3 oxidation state becomes increasingly less stable with respect to the +2 oxidation state on moving from left to right across the first row of the d-block elements.
The variations in oxidation state stability are due to the increase in third ionization energy across the row or period. Third ionization energy increases due to the increase of effective nuclear charge, Zeff which occurs as a result of the inefficient shielding of the d electrons. * As the third ionization energy increases, it becomes energetically less favourable to form the +3 oxidation state *
The transition elements are much denser than the s-block elements and show a gradual increase in density from scandium to copper. This trend in density can be explained by what?
This trend in density can be explained by the small and irregular decrease in metallic radii coupled with the relative increase in atomic mass.
What are the d block elements commonly called? Why?
Transition metals, because they provide a transition between the electropositive metals of the 's' block and the more electronegative metals of the p block from generally left to right across a period (row).
Small increases in ionization energies results in most transition metals having multiple oxidation states. Is this true or false?
True
True or false: D block metals become denser across the period.
True
True or false? 2nd and 3rd row d-block elements in a triad tend to be chemically similar to each other.
True
True or false? The increase in size between 3d and 4d metals is much greater than between 4d and 5d metals.
True
Where can you find the d-block elements on the periodic table?
in Groups 3-12
Following the trend that the sizes of the d orbitals increase in the order of 3d<4d<5d, it is expected that atomic radii will _________ down the group. However, this increase is only observed between rows ________ and _______ of the d-block. Atoms of row 2 and row 3 similar in size due to the______________________________.
increase, 1 and 2, lanthanide contraction
For oxidation states +2 and higher, the E.C. can be found by ________ the 4s electrons plus the appropriate number of 3d electrons.
removing
