Relative Atomic Mass

Relative Mass

The relative mass of an object is the comparison of the mass of the object to the mass of a standard object.

Relative Atomic Mass

The relative atomic mass (Ar) of an element is the average mass of one atom of the element when compared with 1/12 of the mass of an atom of carbon-12, which taken as 12 units.

Relative Atomic Mass

  1. The mass of an atom when compared to another is known as the relative atomic mass (Ar).
  2. The relative atomic mass (Ar) of an element is the average mass of one atom of the element when compared with  1/12 of the mass of an atom of carbon-12, which taken as 12 units.
  3. 1/12 of the mass of an atom of carbon-12 is named as 1 atomic mass unit (amu).
  4. The mass of one carbon atom is 12 amu.
  5. 1/12 of the mass of an atom of carbon-12 is named as 1 atomic mass unit (amu).
  6. The mass of one carbon atom is 12 amu.

Example 1
The mass of a sodium atom is 23 times greater than 1/12 of the mass of carbon-12 atom. What is the relative atomic mass of sodium?

Answer:
23

Example 2:
The mass of element A is twice of the mass of carbon, therefore its relative atomic mass is __________. (Relative atomic mass of carbon = 12)

Answer:
Relative Atomic Mass of Element A = 2 x 12 = 24



Example 3:
An atom of element X is 13 times heavier than one atom of helium. Calculate the relative atomic mass of X.( Ar: He = 4 )

Answer:
Relative Atomic Mass of X = 13 x 4 = 52



Example 4:
How many times that the mass of 2 bromine atoms are greater than 4 neon atoms? (Ar: Ne = 20; Br = 80 )

Answer:
2(80) 4(20) =2
The mass of 2 bromine atoms is 2 time greater than the mass of 4 neon atoms.


Example 5
4 atoms of element L have same mass as 1 tellurium atom. Find the relative atomic mass of L. (Ar: Te = 128 )

Answer:
4L=1(128) L= 128 4 =32
The relative atomic mass of L = 32