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System International base units of measurement

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Base quantity Name Symbol
Area square meter, hectare m2
Time second, minute, hour s
Mass gram, kilogram g
Length meter m
Thermodynamic temperature Kelvin K
Celsius temperature degree Celsius oC
Frequency hertz Hz
Amount of substance mole mol
Volume meter cubed, liter m3
Speed meter per second m/s
Density kilogram per meter cubed kg/m3
Force newton N
Pressure Pascal Pa
Energy joule J
Power watt W
Activity of a radionuclides Becquerel Bq

Every substance has a definite set of properties. Properties are the characteristics by which we can identify something. For example, we know that pure water is a colorless, odorless, tasteless substance that is a liquid under the conditions usually found in an ordinary room. Water puts out fires, and it dissolves sugar and salt. Liquid water can be changed into a gas (called water vapor or steam) by heating it, or into a solid (ice) by cooling it. Salt has a different set of properties from water; sugar has yet another set.

Chemical properties are the characteristic ways a substance can react to produce other substances. Physical properties are the ways a substance can be identified without changing its characteristic composition. For example, water can react with very active metals to produce hydrogen and another compound.

That reactivity is a chemical property of water. Water can also freeze to ice at 0oC (equal to 32oF) or it can evaporate to water vapor, neither of which changes it from H2O. These are physical properties of water. Some properties of a sample of a substance depend on the quantity of the sample. These properties are called extensive properties. For example, the weight of a solid sample depends on how much of the substance is present. Other properties, such as color and taste, do not depend on how much is present. These properties are known as intensive properties. Intensive properties are much more useful for identifying substances.

One of two or more forms of an uncombined element called allotropes; for example, diamond and graphite are allotropes of carbon. Twenty years ago Robert Curl, Harold Kroto, and Richard Smally discovered that carbon exists in a new form, with 60 atoms covalently bonded in the shape of a ball. Some else carbon allotropes are given below:



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Multiplication - умножение | Правила чтения химических формул | BINARY COMPOUNDS | Names of binary compounds. | ISWT 2. | Common Laboratory Apparatus | Chemical properties of acids. | LABORATORY SAFETY RULES | Practical class 7. | Table 2. Numerical Prefixes |

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