Chlorine

In 1774 Swedish pharmacist Carl Wilhem Scheele released a few drops of hydrochloric acid (HCl) onto magnesium dioxide (MgO2).  A greenish-yellow gas arose and though he did not realise it Scheele had discovered chlorine3.

Decades later English chemist Sir Humphrey Davy recognised that the gas was an element. In 1810 he suggested the name 'chloric gas' or 'chlorine' after the Greek word khloros meaning greenish-yellow. Right: Sir  Humphrey Davy (used without permission from www.worcester-aluminium.com)

All elements are shown in the periodic table of the elements (see below), devised by Dimitri Mendeleev. Chlorine is in group VII, the halogens - these elements are highly reactive.  They have seven electrons in their valence shell so react readily with metals that will give up electrons to form an ionic bond.  These ionic compounds have giant lattice structures made up of basic units that repeat thousands of times.  On its own chlorine exists as a diatomic molecule, meaning that two chlorine atoms join together to share a pair of electrons and form a covalent bond with each other.

          

 

 

 

The Periodic Table - here chlorine is in the group labelled VIIA.

(used without permission  from www.ssg.sr.unh.edu/tof/Outreach/Interstellar/why.html)                                                                                                                                               

 

 

As a free element chlorine is a gas that liquefies at -34.04°C and becomes a yellowish crystalline solid at -101.5°C4.  Because of it's highly reactive nature chlorine is often found bound to other elements such as sodium (in rock salt, NaCl, see below).

It is this ability to bind to other elements that make chlorine such a good disinfectant.  It attaches itself to the surfaces of bacteria and viruses and destroys them.  It was first used as a germicide in 1846 when it was used to prevent the spread of 'child bed fever' in the maternity wards of Vienna's General Hospital.

This shows part of the lattice structure of NaCl which has a face-centered cubic structure with both sodium and chlorine atoms being 6 co-ordinate.  Both atoms are therefore said to be 'octahedral'.

 

 

 

(used without permission from www.saltinstitute.org)