Chemical and physical properties of zinc

How it reacts with other elements

[Deposit Photos]

Thanks to its chem­i­cal and phys­i­cal prop­er­ties, zinc is a ma­te­ri­al that is suit­able in a di­verse range of hu­man ac­tiv­i­ties.

How the el­e­ment was dis­cov­ered

Al­loys con­tain­ing zinc have been used by hu­man­i­ty since an­cient times. The name of the met­al (zin­cum) is en­coun­tered in the works of Paracel­sus, a doc­tor who lived in the 16th cen­tu­ry. At around the same time the met­al be­gan to be used by crafts­men in Chi­na, who forged coins from it. Lat­er zinc was dis­cov­ered in Eu­rope, and the met­al be­gan to be wide­ly used in var­i­ous spheres.

The first known al­loy of zinc was brass, which 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 as “white coat­ing” (from Latin), while the word “zinke” meant “point­ed” in Ger­man. The met­al was giv­en its mod­ern name in the 20th cen­tu­ry.

Char­ac­ter­is­tics of the el­e­ment

Zinc is lo­cat­ed in the sec­ond group, side sub­group of the pe­ri­od­ic ta­ble. Its atom­ic mass is 65.38, and atom­ic num­ber is 30. The elec­tron con­fig­u­ra­tion of the out­er shell of the atom is 4s2. Its con­stant and only ox­i­da­tion state is +2. In the pe­ri­od­ic ta­ble, zinc, cad­mi­um, cop­per, man­ganese, chromi­um and oth­ers are tran­si­tion met­als. They in­clude el­e­ments in which elec­trons fill the out­er and next-to-out­er d and f sub­shells.

Met­als of the plat­inum group are also tran­si­tion met­als – ruthe­ni­um, rhodi­um, plat­inum, os­mi­um, pal­la­di­um and irid­i­um. They form com­plex com­pounds, in which they act with dif­fer­ent co­or­di­na­tion num­bers as a com­plex­ing agent. These prop­er­ties are also char­ac­ter­is­tic for zinc. There are five sta­ble iso­topes in na­ture with mass num­bers from 64 to 70. Ra­dioac­tive 65Zn has a half-life of 244 days.

[Deposit Photos]

Phys­i­cal prop­er­ties of zinc

Char­ac­ter­is­tics of the el­e­ment:

  • den­si­ty – 7.13 g/cm³;
  • col­or – bluish-white;
  • zinc is a low-melt­ing met­al, with a melt­ing point of 420 °C;
  • the elas­tic­i­ty and mal­leabil­i­ty of the met­al in­creas­es when it is heat­ed to 100 °C;
  • the boil­ing point of the sim­ple sub­stance is 906 °C;
  • when heat­ed to 200 °C, zinc los­es its elas­tic­i­ty and turns to a gray pow­der;
  • the met­al has a high heat ca­pac­i­ty and heat con­duc­tiv­i­ty;
  • zinc is a good con­duc­tor.

Chem­i­cal prop­er­ties of the el­e­ment

In or­di­nary con­di­tions, the swift re­ac­tion of zinc with air takes place – the met­al is cov­ered with a dull gray coat­ing (zinc ox­ide). Zinc also re­acts with oth­er sub­stances: halo­gens, oxy­gen, chalco­gens, al­ka­lis, acids, am­mo­ni­um and am­mo­nia salts, and also with weak­er met­als. Zinc does not re­act with ni­tro­gen, and is an amor­phic met­al. In re­ac­tions with al­ka­lis, the el­e­ment forms com­plex com­pounds – hy­droxo-zin­cates.

Ex­am­ples of sev­er­al re­ac­tions with zinc

The ba­sis of White’s dis­cov­ery of the zinc ion was the 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 so­lu­tion un­der in­ves­ti­ga­tion. The mag­ne­sium hy­drox­ide re­leased ab­sorbs the com­plex of zinc and ben­zoin, and the sed­i­ment glows with a green light in ul­tra­vi­o­let rays.

When an elec­tric cur­rent is passed through a so­lu­tion con­tain­ing ions, i.e. through the 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 the laws of elec­trol­y­sis dis­cov­ered by Fara­day. For ex­am­ple, if the so­lu­tion con­tains a zinc salt, then on the cath­ode (the elec­trode to which elec­trons move), the zinc ions turn to metal­lic zinc, which are re­leased on the elec­trode. This re­ac­tion can be re­gard­ed as the re­duc­tion of zinc ions by elec­trol­y­sis.

Re­duc­tion of ni­tro group. A few crys­tals or drops of ni­tro com­pounds are mixed with 0.5 M HCl (r=1.12), and met­al 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. Af­ter cool­ing, sev­er­al drops of the ob­tained so­lu­tion 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]

Pet­ten once stud­ied the be­hav­ior of the met­al in re­la­tion to hy­dro­gen chlo­ride dis­solved in var­i­ous or­gan­ic liq­uids. The hy­dro­gen chlo­ride so­lu­tion in thor­ough­ly dried ben­zol re­act­ed en­er­get­i­cal­ly with zinc, but the re­ac­tion stopped as soon as the sur­face was cov­ered with a film of sol­id zinc chlo­ride, which dis­solves poor­ly in ben­zo. If wa­ter is added, which dis­solves the zinc chlo­ride, the re­ac­tion re­sumes. If we ig­nore this de­lay in the re­ac­tion prod­ucts, we may state that hy­dro­gen chlo­ride so­lu­tions in or­gan­ic liq­uid strong­ly re­act with zinc. A so­lu­tion in dry chlo­ro­form re­acts with zinc just as strong­ly as nor­mal aque­ous hy­drochlo­ric acid, al­though the chlo­ro­form so­lu­tion has a very low elec­tro­con­duc­tiv­i­ty, low­er than the elec­tro­con­duc­tiv­i­ty of the air gap. This shows that the cor­ro­sion process is not nec­es­sary con­nect­ed with the flow of an elec­tric cur­rent.

Click here to see won­der­ful ex­perimets with zinc.

Zinc com­pounds

Main cat­e­gories of com­pounds:

  • 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 from the in­ter­ac­tion of zinc with am­mo­nia so­lu­tion;
  • am­pho­ter­ic com­pounds of zinc ox­ide and hy­drox­ide – used for ob­tain­ing com­plex­es of hy­droxo-zin­cates.

Most zinc com­pounds are used in the chem­i­cal in­dus­try and oth­er fields – or­gan­ic syn­the­sis, tech­nol­o­gy, the paint and var­nish in­dus­try. Zinc ox­ide is also used in medicine – it has an anti-in­flam­ma­to­ry ef­fect, and kills bac­te­ria.