Chapter 22, Problem 22.1QP

What characteristics of the transition elements set them apart from the main-group elements?

Interpretation Introduction

Interpretation:

The characteristics of transition elements that set them apart from main group elements have to be described.

Concept Introduction:

In the periodic classification of elements, elements are classified into s-block elements, p-block elements, d-block elements and f-block elements.  The d-block elements (group $3-12$) are referred to as transition elements.  The s-block elements (group $1\text{ and 2}$) and p-block elements (group $13-18$) are known as main group elements.

Answer to Problem 22.1QP

Following are the characteristics that make transition elements unique from main group elements -

• All of the transition elements are metals but all of the main group elements are not metals.
• Transition elements have higher melting points than main group elements.
• Transition elements exhibit more variable oxidation state in its compounds unlike main group elements.
• Transition elements form more colored compounds and paramagnetic compounds than main group elements do.
• Many of transition elements form complex compounds, also known as co-ordination compounds than main group elements do.
• Transition elements have higher densities than main group elements.

Explanation of Solution

Transition elements are metals.  But main group elements are constituted of metals, non-metals and metalloids.

Due to higher density transition elements tend to exhibit higher melting point than main group elements.  For example, Tungsten is a transition element and has melting point $3422 °C$ whereas main group element Lead has melting point $327.5 °C$.

Transition elements tend to form ions with various oxidation states whereas oxidation state of main group elements will not be more than two or three types.  Transition elements exist in zero oxidation state too in its compounds unlike main group elements.  For example, Manganese, a transition element has oxidation state of $+2$ to $+7$ in its compounds whereas main group element such as Sodium has only one oxidation state $+1$ and Lead has $+2$ and $+4$ oxidation states.  Main group elements don't exhibit as many oxidation states than transition elements do.  In compounds like $Ni{(CO)}_4$, Nickel, a transition element is in zero oxidation state whereas  none of the main group element is found to exist in its compounds.

Many of the compounds formed by transition elements are colored unlike the compounds of main group elements. For example, Cobalt (II) chloride is pink in color whereas Tin(II) chloride is colorless.

Figure 1

Many transition elements $Mn,\text{ Ru, Os, Cr, Pt, Pd, Zn, Rh, W, Ir}$ etc, form complex compounds in which transition metal is the central metal ion - ${\left[Fe{\left(CN\right)}_6\right]}^{4-},{\left[Cu{\left(H_{2}O\right)}_6\right]}^{2+},{\left[Co{(N{H}_3)}_{5}Cl\right]}^{2+}$ etc. but there are very less number of main group elements such as Aluminium, Tin, Lead form complex ions.

Conclusion

Transition elements are far different and unique from main group elements in both physical and chemical properties.