Chlorine is a diatomic gaseous element, with the atomic number of 17. Its symbol is Cl and it is a non-metal. As all elements do, chlorine atoms have a unique structure, which will be discussed later in this blog, and many unique uses. It was discovered in 1774 by Carl Scheele, who mistook the gas for a form of oxygen (http://www.lenntech.com/periodic/elements/cl.htm). However, it was the chemist and inventor Humphrey Davy, who named and identified it as an element. The green colour of pure chlorine (in the form of a gas) provided inspiration for Davy, who derived the name chlorine from the Ancient Greek word chloros, which translates to pale green. As aforementioned, chlorine has a number of uses, particularly in cleaning and manufacturing processes. Chlorine is a significant chemical used in mixtures for water purification, disinfectants, bleach, textiles, plastics, medicines and mustard gas (a deadly gas, used by the Nazis in WW1) (https://en.m.wikipedia.org/wiki/Chlorine). Chlorine gas is generally not a health risk to humans. However, a large amount of the element can cause adverse health effects long-term (lung, skin and eye irritation and damage to respiratory system) (http://www.rsc.org/periodic-table)
As all elements do, chlorine has a unique composition and structure. The nucleus of a chlorine atom contains 17 protons and 18 neutrons, and thus the atomic mass of chlorine is approximately 35.5amu (
http://periodictable.com/Properties/A/Density.al.html). Chlorine is a neutral element, with the same number of electrons as protons. The inner energy level, or shell, surrounding the nucleus of the atom contains 2 electrons, the secondary shell contains 8 electrons, and the tertiary shell contains 7 electrons. This element also has a relatively average density of 3.214g/cm^3 (denser than oxygen) (
http://www.chemicalelements.com/elements/cl.html)
Chlorine can be identified by a number of key characteristics. As mentioned above, chlorine gas can have negative health effects when it enters the respiratory system. It's greenish-yellow colour can also help differentiate chlorine form most other gasses. Furthermore, chlorine is a diatomic element, meaning that it consists of two atoms. Chlorine can not be found as a pure substance in nature though, as it has a tendency bonds or mixes with other elements, but is commonly found as a key element in the composition of common salt (
http://www.chemicool.com/elements/chlorine.html). Chlorine also has 16 isotopes with a known half-life which is categorised as "Stable" (
http://education.jlab.org/itselemental/iso017.html). In summary, chlorine is a unique and somewhat easily identifiable element to those who have knowledge or interest in chemistry. To those without the chemist-prowess, however, chlorine can be recognised as the pale green gas which is used in many cleaning and manufacturing products.
