Inert gases : The elements of the zero group of the periodic table are known as inert gases. They are also known as noble or rare gases. The inert gases are six in numbers. They are,
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i) Helium (2He)
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ii) Neon (10Ne)
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iii) Argon (18Ar)
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iv) Krypton (36Kr)
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v) Xenon (54Xe)
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vi) Radon (86Rn)
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Causes of calling inert gases : Each inert gas has the outermost orbit of its atom filled with electron. Such as, 10Ne = 1s22s22p6. Here, the outermost orbit of Neon is filled with electron. So, they do not need to share electrons with other atoms or substances. So, they do not form co-valent bond and they are monatomic. They do not react with other substances and exist only in the free state