Chemical and physical properties of zinc

Reactions with other elements

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Zinc’s chem­i­cal and phys­i­cal prop­er­ties make it a ma­te­ri­al suit­able for a di­verse range of hu­man ac­tiv­i­ties.

How the el­e­ment was dis­cov­ered

Hu­man­i­ty has used al­loys con­tain­ing zinc since an­cient times. The name of the met­al (zin­cum) can be en­coun­tered in the works of Paracel­sus, a doc­tor who prac­ticed medicine in the 16th cen­tu­ry. At around the same time, crafts­men in Chi­na be­gan forg­ing coins from the met­al. Zinc was lat­er dis­cov­ered in Eu­rope and was soon in­tro­duced for wide­spread use in var­i­ous spheres.

The first known al­loy of zinc, brass, was first used in Cyprus, and then in Eng­land, Ger­many, and oth­er Eu­ro­pean na­tions.

Brass astrolabe [Wikimedia]

The name of the met­al comes from the word zin­cum, the et­y­mol­o­gy of which is not en­tire­ly clear. Ac­cord­ing to var­i­ous the­o­ries, zin­cum can be trans­lat­ed from Latin as “white coat­ing,” while the word “zinke” means “tooth” in Ger­man. The met­al re­ceived its mod­ern name in the 20th cen­tu­ry.

El­e­ment char­ac­ter­is­tics

Zinc is lo­cat­ed in group IIB of the pe­ri­od­ic ta­ble. Its has an atom­ic weight of 65.38 g/mol and an atom­ic num­ber of 30. The elec­tron con­fig­u­ra­tion of the out­er­most shell of the atom is 4s2. Its con­stant and only ad­di­tion­al ox­i­da­tion state is +2.

Zinc, like oth­er met­als of the plat­inum group (ruthe­ni­um, rhodi­um, plat­inum, os­mi­um, pal­la­di­um, and irid­i­um), is a tran­si­tion met­al and forms com­plex com­pounds, in which it acts as a com­plex­ing agent. Zinc has five sta­ble nat­u­ral­ly-oc­cur­ring iso­topes with mass­es rang­ing from 64 to 70. Ra­dioac­tive 65Zn has a half-life of 244 days.

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Phys­i­cal prop­er­ties of zinc

Char­ac­ter­is­tics of the el­e­ment:

  • den­si­ty – 7.13 g/cm³;
  • col­or – bluish-white;
  • melt­ing point – 420 °C;
  • elas­tic­i­ty and mal­leabil­i­ty in­crease when heat­ed to ap­prox­i­mate­ly 100 °C;
  • boil­ing point of 906 °C;
  • at tem­per­a­tures above 200 °C, los­es its elas­tic­i­ty and be­comes a grey pow­der;
  • high heat ca­pac­i­ty and heat con­duc­tiv­i­ty;
  • good con­duc­tor.

Chem­i­cal prop­er­ties of the el­e­ment

In or­di­nary con­di­tions, zinc re­acts rapid­ly with air, grad­u­al­ly form­ing a dull grey zinc ox­ide coat­ing. Ad­di­tion­al­ly, zinc re­acts with halo­gens, oxy­gen, chalco­gens, al­ka­lis, acids, am­mo­nia and am­mo­ni­um salts, and even with less ac­tive met­als. Zinc re­acts with both acids and al­ka­lis, mak­ing it an am­pho­ter­ic met­al. When re­act­ing with al­ka­lis, the el­e­ment forms com­plex com­pounds known as hy­droxo-zin­cates.

Ex­am­ples of sev­er­al re­ac­tions with zinc

Zinc ions were dis­cov­ered based on zinc's re­ac­tion with ben­zoin.

Ball-and-stick model of the (S)-benzoin molecule [Wikimedia]

So­lu­tions of sodi­um thio­sul­fate, sodi­um sil­i­cate, mag­ne­sium chlo­ride, and ben­zoin in ethyl al­co­hol are grad­u­al­ly added to the test so­lu­tion. The re­leased mag­ne­sium hy­drox­ide ab­sorbs the com­plex of zinc and ben­zoin, and the pre­cip­i­tate glows green when ex­posed to ul­tra­vi­o­let rays.

When an elec­tric cur­rent is passed through a so­lu­tion con­tain­ing ions, i.e. through an elec­trolyte so­lu­tion, chem­i­cal re­ac­tions take place on the elec­trodes, and the de­gree of the trans­for­ma­tion of this re­ac­tion is con­nect­ed with the amount of elec­tric­i­ty ac­cord­ing to Fara­day’s laws of elec­trol­y­sis. For ex­am­ple, if the so­lu­tion con­tains a zinc salt, then the zinc ions pre­cip­i­tate on the cath­ode (the elec­trode to which elec­trons flow) as metal­lic zinc. This re­ac­tion can be re­gard­ed as the re­duc­tion of zinc ions via elec­trol­y­sis.

Re­duc­tion of the ni­tro group: a few crys­tals or drops of ni­tro com­pounds are mixed with 0.5 M HCl, and metal­lic zinc is added. The re­ac­tion takes place vi­o­lent­ly. When the re­ac­tion dies down, the mix­ture is heat­ed un­til the smell of the ni­tro com­pound dis­ap­pears. The ob­tained so­lu­tion is cooled, and sev­er­al drops are added to an al­ka­line so­lu­tion of cal­ci­um hypochlo­rite Са(OСl)₂. In the course of the re­ac­tion, the ni­tro group is re­duced to an amino group.

Zinc, purity 99.995 % [Wikimedia]

Stud­ies of the met­al's be­hav­ior in re­la­tion to hy­dro­gen chlo­ride dis­solved in var­i­ous or­gan­ic liq­uids re­vealed that hy­dro­gen chlo­ride so­lu­tion in an­hy­drous ben­zene re­acts vig­or­ous­ly with zinc, but the re­ac­tion halts as soon as the sur­face is cov­ered with a film of sol­id zinc chlo­ride, which dis­solves poor­ly in ben­zene. With the ad­di­tion of wa­ter to dis­solve the zinc chlo­ride, the re­ac­tion re­sumes. Dis­re­gard­ing this fact, we may con­clude that hy­dro­gen chlo­ride so­lu­tions in or­gan­ic liq­uids re­act strong­ly with zinc. A so­lu­tion in dry chlo­ro­form re­acts with zinc just as well as nor­mal aque­ous hy­drochlo­ric acid, even though the chlo­ro­form so­lu­tion has very low elec­tri­cal con­duc­tiv­i­ty – low­er than the elec­tri­cal con­duc­tiv­i­ty of the air gap. This demon­strates that the cor­ro­sion process is not al­ways con­nect­ed with the flow of elec­tric cur­rent.

Click here for a se­lec­tion of mes­mer­iz­ing ex­per­i­ments with zinc.

Zinc com­pounds

Main com­pound cat­e­gories:

  • zinc car­bides;
  • zinc halo­genides (flu­o­ride, chlo­ride, bro­mide, io­dide);
  • phos­phide;
  • se­lenide, sul­fite, zinc ar­senide;
  • thio­cyanates, thio­sul­fates, and cyanides – in aque­ous so­lu­tion in the form of cor­re­spond­ing com­plex­es;
  • am­mo­nia com­plex­es – formed by the in­ter­ac­tion of zinc with an am­mo­nia so­lu­tion;
  • am­pho­ter­ic com­pounds of zinc ox­ide and hy­drox­ide – used to ob­tain com­plex­es of hy­droxo-zin­cates.

Zinc com­pounds are most­ly used in or­gan­ic syn­the­sis. They are also used in in­dus­try as com­po­nents of anti-cor­ro­sion agents, al­loys, bat­ter­ies, paints and var­nish­es. Zinc ox­ide is also used in medicine due to its anti-in­flam­ma­to­ry and an­tibac­te­ri­al ef­fects.