A pure substance is a material that has a uniform and definite composition. It can consist of either a single element or a compound. Elements are substances that cannot be broken down into simpler substances by chemical means, whereas compounds consist of two or more elements that are chemically bonded in a fixed ratio.
From what you've mentioned:
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Positive and Negative Ions in a Fixed Ratio: This describes ionic compounds, where cations (positively charged ions) and anions (negatively charged ions) combine in specific ratios to form a stable structure. For example, in sodium chloride (NaCl), sodium (Na⁺) and chloride (Cl⁻) ions combine in a 1:1 ratio.
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One Atom, Two Fuller Molecule: It seems there might be a bit of confusion here. If you meant "fullerene," it is a type of molecule made entirely of carbon, such as C₆₀ (buckminsterfullerene). These are not composed of ions but are part of carbon allotropes.
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Three Hydrogen Bonds for Ionic Compound: Hydrogen bonds are a type of intermolecular force that typically occurs between molecules, not typically within ionic compounds. Ionic compounds are held together by electrostatic forces between positively and negatively charged ions, while hydrogen bonds occur in molecular compounds, often involving hydrogen atoms bonded to highly electronegative elements like oxygen, nitrogen, or fluorine.
In summary, a pure substance can be an element or a compound, and ionic compounds specifically consist of ions in a fixed ratio, whereas hydrogen bonds are more related to molecular compounds rather than ionic ones. If you would like more detail on any specific point or further clarification, feel free to ask!