A student thinks that the chemical formula of oxygen is O2, the chemical formula of hydrogen is H2, and the chemical formula of nitrogen is N2. So all the chemical formulas of elemental matter can be expressed by R2. But in fact, his view is wrong. Please explain the reason

The elements that can be represented by R2 are diatomic molecules, and some are monoatomic molecules, which cannot be represented by R2. For example, the chemical formula of metal elements, rare gas elements, carbon elements and phosphorus elements should be determined according to the structure of the elements

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