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2 types of pure substances

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Answered by GPT-5 mini AI
There are two types of pure substances in chemistry:

1. Elements
- Definition: A substance made of only one kind of atom; cannot be broken down into simpler substances by chemical means.
- Examples: Iron (Fe), oxygen gas (O2), gold (Au), nitrogen gas (N2).
- Notes: Includes single-atom forms (metals, noble gases) and molecular forms (diatomic nonmetals like H2, O2). Allotropes (e.g., graphite and diamond) are different forms of the same element.

2. Compounds
- Definition: A substance made of two or more different elements chemically bonded in a fixed ratio; can be broken down into simpler substances by chemical reactions.
- Examples: Water (H2O), sodium chloride (NaCl), carbon dioxide (CO2), glucose (C6H12O6).
- Notes: Properties differ from the constituent elements; composition is fixed (definite formula).

Quick distinguishing points
- Elements cannot be chemically decomposed; compounds can.
- Elements consist of one type of atom; compounds consist of atoms of different elements in a fixed proportion.
- Both are homogeneous (uniform composition) and have definite physical properties (e.g., melting point).