2) Element symbol: Cl
 

3) Number of electrons, protons, and neutrons: 17 electron, 17 proton, 17 neutrons
 

4) Atomic number: 17
 

5) Atomic mass: 35.453
 

6) Characteristics:

At ordinary temperatures, chlorine is a greenish-yellow gas that may be readily liquefied under pressure of 5170 torr, or 6.8 atmosphere, at 20 °C (68 °F). The gas has an irritating odor and in large concentration is dangerous. (Chlorine was the first substance used as a poison gas in World War I.)
 

7)

History:

Elementary chlorine was first isolated in 1774 by the Swedish chemist Carl Wilhelm Scheele, who thought that the greenish gas was a compound; it wasn't until 1810 that the British chemist Sir Humphry Davy proved that chlorine was an element and gave it its present name.

Three things made from the element:

- used for bleaching paper pulp and other organic materials

- destroying germ life in water

- preparing bromine, tetraethyl lead, and other important products
 

8) Isotopes:

Natural chlorine is a mixture of two stable isotopes: chlorine-35 (75.53 percent) and chlorine-37 (24.47 percent).
 

9) Chlorine is an active element, reacting with water, organic compounds, and many medals.

Chlorine will not burn in air, but it will support the combustion of many substance.

Chlorine and hydrogen may be kept together in the dark, but react explosively in the presence of light.
 

10) Chlorine melts at -101 °C (-149.8 °F) and boils at -34.95 °C (-29.29 °F).