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| Summary |
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 Matter is anything that occupies space and has mass. |
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 Element is a pure substance, which can neither be decomposed nor built from simpler substances by any physical or chemical means. It contains only one kind of atom. |
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 Broadly speaking, elements can be divided into metals, non-metals and metalloids. |
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 A compound can be decomposed into two or more simpler substances. In its formation, energy is usually evolved or absorbed. |
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 The components of a mixture can be separated by simple mechanical means. |
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 The smallest particle of an element or a compound, which can exist in the free state, is called a molecule. |
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 According to Dalton's atomic theory, all matter is made up very small particles called atoms, which cannot be further divided. |
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 The law of constant proportions states that all pure specimens of a compound always contain the same elements combined together in the same proportion by weight. |
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 A mole contains 6.023 x 1023 particles. This is called Avagadro's number. |
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