Chlorine devastating because the existing gas masks were difficult to deploy and had not been broadly distributed. Chlorine is the second halogen, being a nonmetal in group 17 of the periodic table. Its properties are thus similar to fluorine, bromine, and iodine, and are largely intermediate between those of the first two. Chlorine has the electron configuration [Ne]3s3p, with the seven electrons in the third and outermost shell acting as its valence electrons. Like all halogens, it is thus one electron short of a full octet, and is hence a strong oxidising agent, reacting with many elements in order to complete
Fluorine other elements from carbon to magnesium are twenty or more times as common. This is because stellar nucleosynthesis processes bypass fluorine, and any fluorine atoms otherwise created have high nuclear cross sections, allowing further fusion with hydrogen or helium to generate oxygen or neon respectively. Beyond this transient existence, three explanations have been proposed for the presence of fluorine: Fluorine is the thirteenth most common element in Earth's crust at 600–700 ppm (parts per million) by mass. Elemental fluorine in Earth's atmosphere would easily react with atmospheric water vapor, precluding its natural occurrence; it is found only in combined mineral