What is a transition elements?

Transition elements

The transition elements are found in the d block of the Periodic Table, between Groups 2 and 13. However, not all d-block elements are classified as transition elements.

We do not define?scandium?(Sc) and zinc (Zn) as?transition?elements.

• Scandium, with the electronic configuration [Ar] 3d 1 4s 2 , forms only one ion, Sc 3+. This 3 + ion has no electrons in its 3d sub-shell: the?electronic?configuration of Sc 3+ is just its argon core, [Ar].?
• Zinc, with the electronic?configuration?[Ar] 3d 10 4s 2 , forms only one ion, Zn 2+. This 2 + ion has a complete 3d sub-shell: the electronic configuration of Zn 2+ is [Ar] 3d 10 .?

So neither?scandium?nor zinc forms an ion with an?incomplete?d sub-shell. In this chapter we will be looking at the transition elements in the first row of the d block. These are themetals titanium (Ti) through to copper (Cu), according to the?definition?above.

Ions of transition elements

The transition elements are all metals. In common with all metals, their atoms tend to lose electrons so they form positively charged ions. However, each transition metal can form more than one positive ion. For example, the common ions of copper are Cu and Cu2+. We say that the transition metals have variable oxidation states. The resulting ions are often different colours.

Look at the ions of vanadium in their different oxidation states.

Figure: Vanadium and its oxidation states: a a solution containing VO2 + ions, b a solution containing VO2+ ions, c a solution containing V 3+ ions, d a solution containing V 2+ ions.?

Properties of transition elements?

This block of metals includes many you will be familiar with, for example copper, iron, nickel, zinc and chromium

? They are less reactive metals.?

? They form a range of brightly?coloured?compounds?

? They are harder and stronger than the metals in Groups I and II.?

? They have much?higher?densities than the metals in Groups I and II.?

? They have high melting points (except for mercury, which is a liquid at room temperature).?

? They are good?conductors?of heat and electricity.?

? They show catalytic activity as elements and?compounds. For example, iron is used in the industrial production of ammonia gas (see Haber process,).?

? They do not react (corrode) so quickly with oxygen and/or water

? They form simple ions with variable oxidation numbers.?

For example:

– Copper forms Cu+ (Cu(I)) and Cu2+ (Cu(II)), in?compounds?such as Cu2 O and CuSO4 .?

– Iron forms Fe2+ (Fe(II)) and Fe3+ (Fe(III)), in?compounds?such as FeSO4 and FeCl3 .?

– Cobalt forms Co2+ (Co(II)) and Co3+ (Co(III)), in?compounds?such as CoCl2 and Co(OH)3 .

? They form more complicated ions with high oxidation numbers. For ezxample, chromium forms the dichromate(VI) ion, Cr2 O7 2?, which contains chromium with a +6 oxidation number (Cr(VI)) and manganese forms the?manganate(VII) ion, MnO4 ? , which contains?manganese?with a +7 oxidation number (Mn(VII)).

Copper is used in many situations which involve good heat and electrical conduction. It is also used in medallions and bracelets

?This bucket has been coated with zinc to prevent the steel of the bucket corroding

Electronic configurations?transition elements

Table shows the electronic?configurations?of the atoms in the first row of the transition elements. In atoms of the transition elements, the 4s sub-shell is normally filled and the rest of the electrons occupy orbitals in the 3d sub-shell. However, chromium and copper atoms are the exceptions.

Chromium?atoms have just one electron in the 4s sub-shell. The remaining five electrons are arranged in the 3d sub-shell so that each of its five orbitals is?occupied?by one electron.?

Copper atoms also have just one electron in the 4s sub-shell. The remaining ten?electrons?are arranged in the 3d sub-shell so that each orbital is filled by two electro

s.

Table : Electronic configurations of the first row of transition elements.

Most common Oxidation States

It is the similarity in the energy of the 3d and 4s atomic orbitals that make these?variable?oxidation?numbers?possible. Because there are variable oxidation states, the names of compounds containing?transition?elements must have their?oxidation?number included, e.g. manganese(IV) oxide, MnO2 , and cobalt(II) chloride

CoCl2 .

Table : Common oxidation states of the transition elements.?

Physical and chemical properties of the transition elements

The transition elements commonly have physical properties that are typical of most metals:?

1. they have high melting points they have high densities?
2. they are hard and rigid, and so are useful as construction?materials?
3. they are good conductors of?electricity?and heat?
4. they have variable oxidation states?
5. they behave as catalysts they form complex ions
6. they form coloured ions.?

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