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ChemWiki: The Dynamic Chemistry E-textbook > Inorganic Chemistry > Descriptive Chemistry > d-Block Elements > Periodic Trends

Periodic Trends

Transition Metal plays an important role in our society. For example, copper lets us have the electricity in our homes; gold plays an important role in our economy. It is important that we understand the periodic trends of these important metals.

Some important Characteristics of Transition metals

What makes transition metals so unique is the partially filled d orbital. This cause transition metals to make very high melting points(more on this later). Transition metals are metals that are very good at conducting energy which means they are great at conducting heat and electricity. Transition metals can be also be hammered and coiled, in other words, transition metals are malleable and ductile. Transition metals are luster, which means they have a shiny and polished surface. Some important characteristics of Transition metals include:
  • Contain unfilled d orbital
  • Conduct energy (heat, electricity ) very well
  • Malleable and ductile
  • Metallic luster

Periodic trends of Transition Metals

Melting Point

Transition metals have high melting points due to strong metallic bonds. Number of unpaired electrons in the outermost shell indicates the strength of the metallic bonds. Therefore, the more unpaired electrons are present, the higher melting point will be. The first 4 elements in a row always have the highest melting points. However, as the unpaired d orbital electrons pair up, the melting point decreases. The last 5 elements in a row have a lower melting point than the first 4 elements. The last element in each row has the lowest melting point because the d orbital electrons are filled.

As stated above, Zn, Cd, Hg, all have the lowest melting point since their d orbital electrons are occupied.
 
Example 1: Scandium
Lets look at an example between Scandium (Sc) and Zinc (Zn).
Sc: [Ar] 4s² 3d¹ lets take a look at the d orbital:

For Sc we see that there is only one electron in the d-orbital and that electron is unpaired.
Melting point of Sc is 1814 K.
Example 2: Zinc
Now let’s look at Zinc (Zn)
Zn: [Ar] 4s² 3d¹? lets take a look at the d orbital:
For Zn we see that there are no unpaired electrons in the d- orbital.
The melting point of Zn is 692.93 K, which is significantly lower than Sc at 1814 K. This example shows that the number of unpaired electrons does effect the melting point.

The metallic radius

Decreases with the atomic number for the first 5 to 6 elements in a series and the metallic radius increases for the last few elements in a series. (the reason the metallic radius behaves like this is due to the nuclear charge.) As the number of electrons increases, the number of protons in the nucleus increases as well. The number of protons contributes to the nuclear charge, which helps in shielding. As the number of protons in the nucleus increases, the atom is strongly shielding results in decrease of the atomic radius.

Ionization energy

By definition, ionization energy is how much energy is required to remove one electron from an element to the outer shell. Ionization energy increases from left to right due to the number of valance electrons increase from left to right in the periodic table. Ionization energy also increases from bottom to top.

Electronegativity and Bond Polarity

Electronegativity is the ability of an atom to pull electrons to itself. In the periodic table, electronegativity increases from left to right and from bottom to top. In all cases, if electrons are not being shared equally between atoms, the bonds will be polar. On the other hand, if electrons are being shared equally, the bonds will be nonpolar.
 
For example: In water, the oxygen molecule are more electronegative than the hydrogen molecules. Therefore, electrons in the bonds tend to stay longer on the side of oxygen.  The bonds between the oxygen and hydrogen are polar. Furthermore, oxygen has a slightly negative charge while the hydrogen has a slightly positive charge.

Electrode Potential

Electrode Potential is the potential of receiving a electron. The electron potential increases across the series for transition metals. H+ can reduce all transition metals except Cu because Cu has a higher reduction potential than H+. Lets look at the half reactions and the electrode potential for H+, Zn2+ which is a transition metal and Cu which is the exception to the rule.

 
2H+(aq) + 2e-?H?(g) = 0 V
Zn2+(aq) + 2e-?Zn(s)= -.90 V
 Cu+(aq)+e-?Cu(s) = .520 V
 
From this example we can tell that H+ can reduce Zn²+ because Zn2+ has a smaller electrode potential than H+, we also can tell that H+ can not reduce Cu+ because Cu+ has a higher electrode potential than H+.

Magnetism

Since some transition metals have unfilled d electrons, they can also have magnetic properties such as paramagnetic or ferromagnetic. A paramagnetic is not a permanent magnet, but when a magnet field is present it can turn into a magnet. Whereas, ferromagnetic is a permanent magnet. Paramagnetic means that an atom or ion has unpaired electrons and individual magnetic effects do not cancel out. On the other hand, diamagnetic insists that an atom or ion have all the electrons paired with each other and the individual magnetic effects cancel out.
 
The periodic table above shows elements colored according to the type of magnetism they show at room temperature. For example: Mn is a paramagnetic because it has 5 unpaired electrons.

Problems

  1. Which transition metal has a higher melting point Ti or Mn and why?
  2. True or False. Cu can be reduced by H+?
  3. Which transition metal has a bigger atomic radius, V or Fe?
  4. What unique trait gives transition metal there ability to form magnets?
  5. True or False. Transition metals are bad at conducting heat and electricity? 
  6. Is Zn diamagnetic or paramagnetic?

Answers

  1. Ti has higher melting point because it has 2 unpair electrons, Mn has no unpaired electrons.
  2. False, Cu is the only transition metal that is not reduced by H+.
  3. V has a greater atomic raduis than Fe because radius decrease with atomic number. V has a bigger atomic number than Fe.
  4. The trait is most transition metal have unfilled d orbitals.
  5. False. Transition Metals are great at conducting heat and electricity.
  6. Zn is diamagnetic because all of its electrons in the electron configuration are paired.

References

  1. Petrucci, Ralph. General Chemistry: Principles & Modern Applications. 9th ed. Upper Saddle River, New Jersey 2007.
  2. Zener, C. Interaction Between the d-shell in the Transition Metal. Physical Review. 81.4 (1951).

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Last Modified
11:49, 12 May 2014

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