1. Distinguishing Among Atoms
4.3

2. Standards/Objectives Students Will Be Able To:
1a: Relate the position of an element in the periodic table to its atomic number and atomic mass
Calculate the # of electrons, protons, neutrons, and atomic mass of atoms

3. Atoms Elements have different # of protons or electrons
Elements are NEUTRAL
Everyone think, what do I mean by that?
I will call on someone to answer
# protons (+) = # electrons (-)
Positive charge of protons = Negative charge of electron

4. Atomic Number Top # on periodic table Atomic # = # of protons
Since # protons = # electrons
Therefore atomic # also equals # electrons

5. Atomic Number
Everyone think of the following questions (don’t answer yet):
What is lithium’s atomic number?
How many protons does lithium have?
How many electrons does lithium have? 3 3 3

6. Mass Number Bottom # on periodic table rounded to WHOLE #
Average atomic mass rounded to whole #
Where is most of the MASS in an atom?
Nucleus
Neutrons (no charge) and protons (+ charge)
Mass # = # neutrons + # protons
Mass # = ~ 7

7. # Neutrons # neutrons = mass # - atomic # (neutrons + protons)OR
(electrons)

8. Example What is the atomic # of lithium?
What is the mass # of lithium?
How many protons, electrons, and neutrons does lithium have?
Protons = 3 (atomic #)
Electrons = 3 (atomic #)
Neutrons
# neutron = mass # - atomic #
Mass # = Bottom # or (average atomic mass) rounded to whole #
6.941 ~ 7
# neutron = = 4

9. Now You Try Find the atomic #, mass #, # protons, electrons, and neutrons
Beryllium
Neon
Sodium
Beryllium = Be
Atomic # = 4
Mass # = ~ 9
# protons = 4
# electrons = 4
# neutrons = 9 – 4 = 5

10. Now You Try Find the atomic #, mass #, # protons, electrons, and neutrons
Beryllium
Neon
Sodium
Neon = Ne
Atomic # = 10
Mass # = ~ 20
# protons = 10
# electrons = 10
# neutrons = = 10

11. Now You Try Find the atomic #, mass #, # protons, electrons, and neutrons
Beryllium
Neon
Sodium
Sodium = Na
Atomic # = 11
Mass # = ~ 23
# protons = 11
# electrons = 11
# neutrons = = 12

12. Shorthand Ways of Writing
mass #
108Ag 47
atomic #
# protons = 47
# electrons = 47
# neutrons = = 61

13. Shorthand Ways of Writing
Carbon - 12
element name
mass #
(bottom #) rounded to whole #
OR (average atomic mass) rounded
to whole #)

14. Isotopes Isotopes = Atoms with DIFFERENT # of neutrons
Different mass # = # proton + # neutron
Same # electrons and protons
Mass # = 10p + 10n
= 20
Neon-20
20Ne 10
Mass # = 10p + 11n
= 20
Neon-21
21Ne 10
Mass # = 10p + 12n
= 20
Neon-22
22Ne 10

15. Now You Try Find the following: Atomic # 2) Helium-4 Mass #
# protons
# electrons
# neutrons
1) 32S 16
2) Helium-4
3) Manganese
4) 16O 8
5) Copper
6) Chlorine-37

16. Atomic Mass Unit Atomic mass unit (amu)
Used as a standard for masses of atoms
Carbon-12 is exactly 12 atomic mass units (amu)
1 amu = one-twelfth or (1/12) mass of carbon-12
Helium-4 is 1/3 of the mass of carbon-12
Nickel-60 is about 5 times larger than the mass of carbon-12

17. Average Atomic Mass Most atoms have many isotopes
Average atomic mass is the weighted mass of the different isotopes
Reason why average atomic mass is a decimal #

18. Calculating Atomic Mass
ExampleMultiply mass of each isotope by its natural abundance (decimal) AND add the products
: Calculate the atomic mass of carbon.
Isotope
Natural Abundance
Atomic mass
Carbon-12
98.89%
amu
Carbon-13
1.11%
amu

19. Isotope Natural Abundance Atomic mass
Carbon-12
98.89%
amu
Carbon-13
1.11%
amu
Atomic mass carbon = (atomic mass carbon-12) + (atomic mass carbon-13)
Atomic mass carbon = = ~ amu

20. Now You Try Calculate the atomic mass for the following.
Chlorine
Chlorine-35
75.77%
amu
Chlorine-37
24.23%
amu
Oxygen
Oxygen-16
99.759%
amu
Oxygen-17
0.037%
amu
Oxygen-18
0.204%
amu
Chlorine = amu
Oxygen = amu