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    I'm currently doing some chemistry questions (page 18 of OCR AS & Year 1 textbook).

    This is the question:

    Write a balanced with state symbols for the following reaction:

    Magnesium reacts with solid phosphorus to form solid magnesium phosphide.

    The answer, according to the back of the book says:

    6Mg + P⁴ → 2Mg³P²


    My question is how can you know or work out that solid Phosphorus in the product has four atoms? Same goes the Mg and the P in the result have their respective 3 and 2 atoms (all before balancing out the equation).
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    (Original post by Grashex)
    I'm currently doing some chemistry questions (page 18 of OCR AS & Year 1 textbook).

    This is the question:

    Write a balanced with state symbols for the following reaction:

    Magnesium reacts with solid phosphorus to form solid magnesium phosphide.

    The answer, according to the back of the book says:

    6Mg + P⁴ → 2Mg³P²


    My question is how can you know or work out that solid Phosphorus in the product has four atoms? Same goes the Mg and the P in the result have their respective 3 and 2 atoms (all before balancing out the equation).
    It's just something that you have to learn...

    Phosphorus exists as simple P4 pyramidal molecules, sulfur as S8 crown shaped molecules.

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