ATOMIC MASS

What is "atomic mass?"
Well, first off it is the mass of 1 mole of atoms in an element.
And second of all, the masses of any element can be found on the periodic table. To specifically see it, you will be able to find the mass on the very bottom of each box of an element.
On the diagram to the left, the mass of Boron is 10.811, Carbon is 12.01115, Nitrogen is 14.0067 and so on.






How do you find the "Molecular mass" of an element or compound?

• To find the molecular mass of a diatomic element, you will need to, first, find the atomic mass of the element, and secondly multiply it by TWO considering it is DIatomic.

Examples:
N2 => 2 Nitrogen => 2(14.0) =>28 g/mol
I2 => 2 Iodine => 2(126.9) => 253.8 g/mol
H2 => 2 Hydrogen => 2(1.0) => 2.0 g/mol

• To find the molecular mass of a monoatomic element, it is as simple as finding the molecular mass of a diatomic element or compound. The only change to it, is that you must multiply it by ONE, considering it is MONOatomic.

Examples:
Si = > 1 Silicon => 1(28.1) => 28.1 g/mol
Fe => 1 Iron => 1(55.8) => 55.8 g/mol
Ne => 1 Neon => 1(20.2) => 20.2 g/mol

How do you find the "molar mass" of compounds?
To find the molar mass of any compound of an element, it's as simple as figuring out the molecular mass of a monoatomic or a diatomic element. First of all, you need to find the molecular mass of the all the elements in the formula then simply add both molecular masses together, which will give you your final result - molar mass.

Example:
H20=>
2 H => 2(1.0) => 2.0 g/mol
+
1 O => 1 Oxygen => 1(16.0) => 16.0 g/mol =>
= 18.0 g/mol

How do you convert MASS into MOLES?
It's simple, easily use the conversion factor!

g
mol
or
mol
g

Examples:
Find the mass of 2.5 mol of water
Since we already know that ... H2O => 18.0 g/mol
We can use our new method:
1 mol
18.0 g
x
1 g
2.5 mol
= 45 g

Find the number of moles in a 391 g sample of nitrogen dioxide
No2 =>
1 N => 1(14.0)
2 O => 2(16.0)
=> 46 g/mol

1 mol x 391 g = 8.5 mol
46 g

HOMEWORK FOR NEXT CLASS: Unit 3 worksheet #1-4 ALL