Atomic number 28

Introduction :
d – block elements are also called transition elements. Transition metals are those elements which contain partially filled d- sub shells either in their atoms or in their common oxidation states. Nickel is a silvery white metal and takes a high polish. Nickel is hard malleable, ductile, ferromagnetic and fair conductor of heat and electricity. Atomic number 28 belongs to Iron – cobalt group. 'Ni' is commercially obtained from pentlandite and pyrrholite of the subdury region of Ontario.
Characteristics of Atomic number 28:

• The element in the periodic table which has atomic number 28 is Nickel. 
• 'Ni' has mass number 58.6934. 
• 'Ni' has oxidation state of 2 and 3. 
• Atomic number 28 has electronic configuration [Ar]4s²,3d⁸. 
• Nickel has chemical formula ‘Ni’.
• Atomic number 28 belong to Period 4 and Group 10.
• 'Ni' belongs to d - block elements. 

Properties of atomic number 28:

• Oxidation states of 'Ni': The elements exhibit variable oxidation states depending on the number of electrons participating in the bonding. Ni has oxidation states 2 and 3. 
• Colors of transition metal ions:  When the visible light of wavelength 400 to 700 nm is passed through a solution of a transition metal compound, it absorbs a particular frequency of radiation and transmits the remaining colors.
• Magnetic properties of 'Ni':  The paramagnetic behavior is highly pronounced in case of iron, cobalt and nickel. Hence they are called ferromagnetic substances.
• Formation of complexes by 'Ni': These metal ions have a great tendency to combine with a large number of molecules or ions called ligands and form complexes. The bond between a metal ion and a ligand is coordinate. Hence, complex compounds are also known as coordination compounds.
• Chemical reaction: Nickel carbonyl can be oxidized, Chlorine oxidizes nickel carbonyl into NiCl₂, releasing carbon monoxide gas.

               2Ni(CO)₄  +  2ClCH₂CH=CH₂    ====>  Ni₂(μ-Cl)₂ (η³-C₃H₅)₂  +  8CO

• Catalytic properties of transition metals: Many transition metals and their compounds are used as catalysts in several inorganic and organic chemical reactions. Nickel catalyst is used in the hydrogenation of oils.                                                                                       Oils +  H₂    →  Fats
• Isotopes of Nickel: ⁵⁸Ni, ⁶⁰Ni, ⁶¹Ni, ⁶²Ni and ⁶⁴Ni are five stable isotopes of Nickel. ⁵⁸Ni being the most abundant.  ⁶²Ni is one of the most stable nuclides.
• Reaction of 'Ni' with halogens:

             Ni_(s)    +    cl_2(g)   ====>    NiCl_2(s)     (Yellow)
             Ni_(s)    +    Br_(g)    ====>    NiBr_2(s)     (Yellow)
             Ni_(s)    +    I_2(g)     ====>    NiI_2(s)       (black)

• Reaction of Nickel with acids:

             Ni_(s)     +   H₂SO_4(aq)  ====>  Ni²⁺_(aq)  +  SO^2-_(aq)  +  H_2(g)  

• Reaction of Nickel with air:

    Nickel metal does not react with air under normal condition. Finely divided Nickel metal readily reacts with air. At higher temperatures, the reaction appears not to proceed to completion but give some nickel(ll) oxide.
            2Ni_{(s)    +}    O_2(g)    ====>  2NiO_(s)                                                                                        

Uses of Atomic number 28:

• It is used in many industrial and consumer products, including stainless steel, magnets, coins, rechargeable batteries, electric guitar strings and special alloys. 
• 'Ni' is used in plating and as a green tint in glass. 
• Atomic number 28 is a metal alloy and its chief use in the nickel steels and nickel cast iron. 
• 'Ni' is widely used in many alloys, such as nickel brasses and nickel bronze. etc.
• Raney Nickel, a finely divided form of metal is alloyed with aluminum which absorbs hydrogen gas.