<span>The </span>octet rule<span> is a chemical </span>rule<span> of thumb that reflects observation that atoms of main-group elements tend to combine in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas.
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A metal rail rusting in damp weather.
Answer:
3 elements
Calcium,oxygen and hydrogen
Answer:
1. Dmitri Mendeleev
2. Johann Dobhereiner
3. John Newlands
4. Henry Moseley
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