1. Counting Atoms
Chapter 3
Section 3

2. Atomic Number Atomic number: the number of _______ of each atom
Represented by “____”
The atomic number ____________ the element.

3. Isotopes
Isotopes: atoms of the ______element that have ____________masses
Isotopes have the same number of ______ and ____________, but a different number of ____________.
Most elements naturally have __________ isotopes

4. Mass Number
Mass number: the total number of _____ and ________that make up the _______ of an isotope
Mass number = ____ + _____
Isotopes are usually identified by specifying their ________number.

5. Designating Isotopes There are two methods to specify isotopes
Method 1 is called ___________: write the name of the element, then a hyphen, then the mass number
Method 2 is called the ____________: in front of the symbol of the element, _________the mass number and _______ the atomic number

6. Hydrogen
Hydrogen is special in that it also has specific names for each isotope
Hydrogen with only 1 p+ and no n0 is called ________, hydrogen-___,
Hydrogen with 1 p+ and 1n0 is called __________, hydrogen-___,
Hydrogen with 1 p+ and 2 n0 is called __________, hydrogen-___,

7. Practice: name the isotope both ways
helium with 1 neutron
carbon with 7 neutrons
oxygen with 8 neutrons
uranium with 142 neutrons
__________,
___________,

8. More Practice
How many protons, electrons, and neutrons are there in an atom of chlorine-37?
_______________________________
How many protons, electrons, and neutrons make up an atom of bromine-80
Complete worksheet here on atomic notation

9. Relative Atomic Masses
If we express the mass of atom in _____, it would be extremely ________.
__________mass is used instead.
___________is the standard atom and has been assigned a mass value of exactly 12 ______________ (______)

10. More about Relative Atomic Mass
All other atomic masses are determined by comparing it with the mass of the carbon- 12 atom
See Table 4 in this section for some typical atomic masses
The masses could also be expressed by adding up the relative masses of the e-s, p+s, and n0s

11. Average Atomic Mass
______atomic mass: the __________of the atomic masses of the naturally occurring __________of an element.
The average atomic mass depends on both the ________and the ______________of each of the element’s isotopes.

12. Calculating Average Atomic Mass
Copper consists of 2 naturally occurring isotopes
A sample of copper contains 69.15% of copper-63 ( amu) and 30.85% of copper-64 ( amu)
Express the percentages as _______values.
52.3% is expressed as ________

13. Continued Solve like this:
_________________________________ _________________________________
________________________________
Can round value to 2 decimal places

14. The Mole The SI unit for the _______of a substance
________: the amount of a substance that contains as many particles as there are atoms in exactly _____g of _________.
It is a ___________unit like dozen, score, gross, etc.

15. Avogadro’s Number
_____________________: the number of particles in exactly one mole of a pure substance
NA = _________________particles

16. Conversions with Avogadro’s Number
Since _______________is the number of particles in a mole, that can be used as a _________________factor.
Work practice problems and see the book for sample problems.

17. Basic Mole Problems
How many atoms are found in an iron sample that is 3.5 moles?
How many moles are in a sample of lead that contains 4.56 x 1025 atoms?

18. Molar Mass Molar mass: the mass of one _______of a pure substance
Usually written in units of _________.
The molar mass of an element is numerically equal to the _____________of the element in atomic mass units (found on the periodic table).

19. More about Molar Mass
Molar mass is usually rounded to two decimal places.
What is the molar mass of carbon?
What is the molar mass of chlorine?

20. Gram/Mole Conversions
The molar mass can be used as a ________________factor.
Work practice problems
Next Slide
See the book for sample problems
What is the mass in grams of 3.50 mol of copper? 222g Cu
A chemist produced 11.9 g of Al. How many mol of Al were produced? mol Al

21. Simple Practice What is the mass in grams of 3.50 mol of copper?
A chemist produced 11.9 g of Al. How many mol of Al were produced?