# Distinguishing Among Atoms

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Distinguishing Among Atoms
4.3

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 #

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

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

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