Transition Element

What is Transition Element?

A metal from the central block of the Periodic Table, between Group II and Group III. Transition elements have high densities and high melting points, form coloured compounds, and often act as catalysts, either as the element itself or as one of its compounds. Extended candidates also describe their ions as having variable oxidation numbers, including iron(II) and iron(III).

This definition is part of the The Periodic Table chapter in Cambridge IGCSE Chemistry.

Concepts related to Transition Element

• central block
• coloured compounds
• Catalyst

Common mistakes with Transition Element

• 3 · “Group number = ion charge” applied everywhere Defect Deducing a \(+4\) ion for carbon, or a \(+7\) ion for chlorine, by reading the group number as the charge. Fix The relationship holds for Groups I, II and III (charge \(=\) group number, positive) and for Groups V, VI and VII (charge \(=\) group number \(-\,8\), negative). Group IV and the transition elements do not follow it, and Group VIII normally forms no ions at all.
• 8 · “All transition metal compounds are coloured” Defect Turning a typical property into a universal law, and then using it to reject a correct identification. Fix Transition elements form coloured compounds and are often catalysts. Neither statement is “always”. Titanium(IV) oxide, the white pigment in paint, and scandium oxide are both white solids. One property alone never classifies an element — look for the cluster.
• Error 4 · “Carbon is in Group IV, so it forms \(\mathrm{C^{4+}}\) ions.” Defect The group-to-charge rule applied outside its range. Chemistry Four outer electrons is equally far from losing all of them and from gaining four. Group IV elements normally share electrons instead, forming covalent bonds as in \(\mathrm{CO_2}\) and \(\mathrm{CH_4}\). Repair The rule covers Groups I–III and V–VII. Group IV is an exception, and so are the transition elements. Transfer What ion does silicon \((2,8,4)\) form in its simple compounds? None — it shares.
• Error 5 · “Iron is in the eighth column, so its ion is \(\mathrm{Fe^{8+}}\).” Defect Main-group reasoning applied to a transition element. Chemistry The group-number-to-charge rule covers Groups I–III and V–VII only. The transition elements sit outside it entirely, so no charge can be deduced from a column count. Repair For a transition element, read the charge from the name or the formula of the compound — never from a column count. Transfer What is the charge on the copper ion in copper(II) sulfate? \(+2\). Supplement — Extended candidates Supplement 8.4.2 Why The reason no single charge follows from the position is that transition elements have ions with variable oxidation numbers. Iron forms \(\mathrm{Fe^{2+}}\) and \(\mathrm{Fe^{3+}}\), so there is no one answer for the question to have. A Core candidate needs the rule's limit; an Extended candidate needs the reason as well.
• Error 17 · “All transition metal compounds are coloured, so a white compound rules it out.” Defect A typical property hardened into a universal law, then used backwards. Chemistry Transition elements form coloured compounds and are often catalysts. Neither is “always”: titanium(IV) oxide is the white pigment in paint. And a property that is typical of a class cannot be used to exclude a member on one counter-example. Repair Classify on the cluster: high melting point, high density, coloured compounds, catalysis. (Extended candidates add variable oxidation number as a fifth.) Transfer A metal melts at \(1668\,{}^\circ\mathrm{C}\), has density \(4.51\;\mathrm{g/cm^3}\), and forms a white oxide. Transition element? Probably yes — two strong signals, and one white compound does not rule it out.

Examiner tips on Transition Element

• What a three-property answer needs. For “give three properties that show \(\mathrm{Y}\) is a transition element”, the answer needs three distinct properties each tied to the data you were given — not to three ways of saying “it is dense”. Scan the four Core properties and pick the ones the question has actually supplied evidence for; Extended candidates have a fifth to scan as well.