Atomic Mass Unit Scale

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The scale in which the relative atomic masses of different atoms are expressed is called atomic mass unit scale.

Modern definition of atomic mass unit

The mass of 1/12 part of ¹²C isotope of carbon is equivalent to one atomic mass unit.

Relative atomic mass

The atomic mass of an element is a relative quantity and is the mass of one atom of the element relative to 1/12 the mass of one carbon-12 atom. Thus,

Modern definition of atomic mass of an element

Gram Atomic Mass (GAM)

The atomic mass of an element expressed in grams is called the gram atomic mass of an element. It is also called gram atom.

Example: The gram atoms present in 46 grams of sodium

Significance of a symbol of an element

Qualitative

• It represents a specific element.

• It represents one atom of an element.

Quantitative

• It represents how many times an atom is heavier than one atomic mass unit.

• It represents one gram - atom of an element.

• It represents how many atoms are present in one gram atom (1 mole).

For example, 12 grams of carbon has 6.023 x 10²³ atoms in it.