COUNTING UNITS FOR ……. atoms. These slides will help you navigate the next section of the Counting Units Lab – Experiment #5/Unit 2 (B): Mole System . Have a sheet of paper on which to answer questions and work problems. You will turn in your work at the end of the class period.
These slides will help you navigate the next section of the Counting Units Lab –
Experiment #5/Unit 2 (B):
Have a sheet of paper on which to answer questions and work problems. You will turn in your work at the end of the class period.
Chemists also use a counting unit:
to “measure” out numbers of atoms.
This counting unit is called the mole.
Just like all counting units, it is a NUMBER:
6.02 x 1023
This is quite a large number: write it out on your paper. I’ll wait………………………………………………………
Check it out….
Just a couple more:
If 10 billion chickens each laid 10 eggs per day, it would take….................> 10 billion years to produce 1 mole of eggs…
One mole of those chicken eggs would fill all the oceans on earth…. 30 million times….
The Periodic Table contains the relative masses of all the atoms……
Masses represent masses of atoms and are given in atomic mass units (amu).
Our mass of one grain of rice corresponds to the atomic mass unit of the periodic table.
The relative masses on the periodic table are based on the “standard”: the carbon-12 isotope. The masses of atoms of all the other elements are “relative” to the mass of an atom of carbon-12.
An atom of sulfur has a mass of ______ amu.
It’s mass is ______ X the mass of an atom of hydrogen.
Whyis the mole counting unit so very large?
(6.02 x 1023)
Because atoms are so very small, and it takes so very, very, very many of them to give the relative mass, in grams.
We chemists measure atoms in grams..
When we weigh out a relative mass of atoms in grams, we are measuringmolesof atoms !!
A relative mass on the periodic table inamu= mass of one atom.
A relative mass on the periodic table in grams = mass of one mole of atoms.
Measured mass of one…..
Unit of mass
We call it …
Atomic mass unit
Atomic mass unit – used to describe masses of single atoms (protons + neutrons).
Grams – used to describe masses of moles of atoms.
Recall – from our Model System:
(a) the relative mass of any seed-type contained the
same number of seeds (the counting unit)
And so, in the Mole system:
(b) the relative mass of any atom-type contains the
same number of atoms (6.02 x 1023)
Where does the counting unit for atoms
(Avogadro’s number = 6.02 x 1023)
Our model seed system showed us that the counting unit describes a relationship between the relative mass and the actual mass :
relative mass = counting unit
Let’s start with Hydrogen:
How many atoms are in one relative mass of hydrogen (1.0 g)?
1. Relative mass = 1.0 gActual mass = 1.7 x 10-24 g (H has 1 p+)
2. relative mass = 1.0 g___________ = 5.9 x 1023 atoms
actual mass 1.7 x 10-24 g/atom
Mass of 1 proton (p+):1.67 x 10-24 gMass of 1 neutron (n0):1.67 x 10-24 g
Turn to page 2 of Exp’t 5/Unit 2(B) handout and complete table:
Use masses of protons and neutrons given to sum up actual mass for each atom.
Atom# protons# neutronsmass of atom
C 6 6
N 7 7
O 8 8
Cl 9 10
Ar 18 22
Complete the table for the elements given, then add 2 more
of your choice from the periodic table!
Check answers on the next slide…………………………………………
Avogadro’s number, the mole, 6.02 x 1023
converts the masses of atoms on the periodic table (amu)
into masses of moles of atoms (g) !
Some useful conversion factors:
1 mole = 6.02 x 1023 atoms
1 mol = relative mass (g)
e.g.,C12.01 g/mol atoms
Na 1 mol atoms/23.0 g
Solve:How many grams in 0.50 mol S?
0.50 mol32.1 g_______ = 16.1 g S
1 mol S atoms
When you have finished the practice problems, turn in your paper and begin the Calculations and Questions for part (B) of Exp’t 2.5.