2.1.3 Atomic Masses Flashcards
Define relative isotopic mass.
Mass compared with 1/12th mass of C-12
Define relative atomic mass.
Weighted mean mass compared with 1/12th mass of C-12.
Define u.
- The unified atomic mass unit;
- The mass of a C-12 atom is defined as 12U - so 1/12 C-12 mass is u.
- This is the mass of
- 660540210x10^-27kg
What is special about the relative atomic mass in an isotope? What major assumptions does this make?
The relative isotopic mass is the same as the mass no;
1. Neglecting the tiny contribution of electrons to the mass of the atom and
2. Assuming that pr/ neut masses are both 1u.
So:
- Relative isotopic mass of O-16 is 16;
- Relative isotopic mass of Na-23 is 23;
What is relative atomic mass?
Ar is THE WEIGHTED MEAN MASS OF AN ATOM OF AN ELEMENT COMPARED WITH 1/12 OF THE MASS OF AN ATOM OF CARBON-12
- this is combining the %age contributions / masses of different isotopes, eg with Cl, to create an overall mass.
What is weighted mean mass?
We use this term to account for the contribution made by each isotope to the overall mass of an element.
What does the contribution made by an isotope to the overall mass of an element depend on?
- % age abundance of the isotope;
2. RAM of the isotope;
How would one calculate the relative atomic mass of bromine?
- 53% Br-79
- 47% Br-81
Ar (Br)= (0.53x79)+(0.47x81)
Define relative isotopic mass.
THE MASS OF AN ATOM OF AN ISOTOPE COMPARED WITH ONE-TWELFTH OF THE MASS OD AN ATOM OF CARBON-12.
What is relative molecular mass?
Do the sums of the RAMs of different elements - ie H2O= (2x1)+16
What is the difference between relative molecular mass and relative formula mass?
They are calculated in the same way, but relative molecular mass is for simple molecules and relative formula mass is for describing giant structures.
