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Relative Atomic Mass and Relative Molecular Mass

 
3.1 Relative Atomic Mass and Relative Molecular Mass
 
Definition of Relative Atomic Mass, RAM

The average mass of an atom of the element compared to \(\dfrac{1}{12}\) of the mass of one carbon-\(12\) atom.

\(\color{black}\,\\\text{Relative atomic mass of an element}=\dfrac{\text{Average mass of one atom of the element}}{\dfrac{1}{12} \times \text{Mass of one carbon-12 atom}} \\ \,\\\)
 
This image is an infographic titled ‘CARBON-12 USED AS THE STANDARD REFERENCE.’ It is divided into three sections: 1. The first section states, ‘Carbon-12 is a solid at room temperature and thus can be handled easily.’ 2. The second section mentions, ‘Carbon-12 combines easily with other elements.’ 3. The third section indicates, ‘Carbon-12 is found in most substances.’ The infographic is branded with the ‘Pandai’ logo on the top left corner. The background is light blue with red and white accents.
 
Definition of Relative Molecular Mass, RMM

The average mass of the molecule compared to \(\dfrac{1}{12}\) of the mass of one carbon-\(12\) atom.

\(\text{Relative molecular mass of a substance}=\dfrac{\text{Average mass of one molecule}}{\dfrac{1}{12} \times \text{Mass of one C-12 atom}} \\ \,\\\)
 
Calculation of Relative Molecular Mass, RMM
The relative molecular mass of a molecule can be calculated by adding up the relative atomic masses of all the atoms that form the molecule.
 
Example of Calculation of Relative Molecular Mass, RMM
\(\color{black}\text{RMM of oxygen gas, }\text{O}_2 \\=2(\text{RAM of }\text{O})\\=2(16)\\=32\) \(\color{black}\text{RMM of water,}\,\text{H}_2\text{O}\\=2(\text{RAM of }\text{H})+\text{RAM of }\text{O}\\=2(1)+16\\=18\)
 
Definition of Relative Formula Mass, RFM
The relative mass of an ionic substance is called the relative formula mass, RFM.
 
Example of Calculation of Relative Formula Mass, RFM
  • The relative formula mass is calculated by summing up the relative atomic masses of all the atoms shown in the formula of the ionic substance.
     
  • Example:
    [Relative atomic mass: \(\text{O=16, Al=27, S=32, Cl=35.5, Zn=65}\)]
    \(\text{RFM for zink chloride, }\text{ZnCl}_2\\ =\text{RAM of Zn}+\text{2(RAM of Cl)}\\ =65+2(35.5)\\=65+71\\=136 ​ ​\)
 

 

 

 

 

The views expressed in the notes here are those of the contributor and don’t necessarily represent the views of pandai.

Relative Atomic Mass and Relative Molecular Mass

 
3.1 Relative Atomic Mass and Relative Molecular Mass
 
Definition of Relative Atomic Mass, RAM

The average mass of an atom of the element compared to \(\dfrac{1}{12}\) of the mass of one carbon-\(12\) atom.

\(\color{black}\,\\\text{Relative atomic mass of an element}=\dfrac{\text{Average mass of one atom of the element}}{\dfrac{1}{12} \times \text{Mass of one carbon-12 atom}} \\ \,\\\)
 
This image is an infographic titled ‘CARBON-12 USED AS THE STANDARD REFERENCE.’ It is divided into three sections: 1. The first section states, ‘Carbon-12 is a solid at room temperature and thus can be handled easily.’ 2. The second section mentions, ‘Carbon-12 combines easily with other elements.’ 3. The third section indicates, ‘Carbon-12 is found in most substances.’ The infographic is branded with the ‘Pandai’ logo on the top left corner. The background is light blue with red and white accents.
 
Definition of Relative Molecular Mass, RMM

The average mass of the molecule compared to \(\dfrac{1}{12}\) of the mass of one carbon-\(12\) atom.

\(\text{Relative molecular mass of a substance}=\dfrac{\text{Average mass of one molecule}}{\dfrac{1}{12} \times \text{Mass of one C-12 atom}} \\ \,\\\)
 
Calculation of Relative Molecular Mass, RMM
The relative molecular mass of a molecule can be calculated by adding up the relative atomic masses of all the atoms that form the molecule.
 
Example of Calculation of Relative Molecular Mass, RMM
\(\color{black}\text{RMM of oxygen gas, }\text{O}_2 \\=2(\text{RAM of }\text{O})\\=2(16)\\=32\) \(\color{black}\text{RMM of water,}\,\text{H}_2\text{O}\\=2(\text{RAM of }\text{H})+\text{RAM of }\text{O}\\=2(1)+16\\=18\)
 
Definition of Relative Formula Mass, RFM
The relative mass of an ionic substance is called the relative formula mass, RFM.
 
Example of Calculation of Relative Formula Mass, RFM
  • The relative formula mass is calculated by summing up the relative atomic masses of all the atoms shown in the formula of the ionic substance.
     
  • Example:
    [Relative atomic mass: \(\text{O=16, Al=27, S=32, Cl=35.5, Zn=65}\)]
    \(\text{RFM for zink chloride, }\text{ZnCl}_2\\ =\text{RAM of Zn}+\text{2(RAM of Cl)}\\ =65+2(35.5)\\=65+71\\=136 ​ ​\)
 

 

 

 

 

The views expressed in the notes here are those of the contributor and don’t necessarily represent the views of pandai.
Chapter : Mole Concept, Chemical Formulae and Equations
Topic : Relative Atomic Mass and Relative Molecular Mass
Form 4 Chemistry
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