Distinguishing Among Atoms

4.3

Standards/ObjectivesStudents 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 electronsElements 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 tableAtomic # = # of protonsSince # protons = # electronsTherefore 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?

33

3

Mass NumberBottom # on periodic table rounded to WHOLE #Average atomic mass rounded to whole #

Where is most of the MASS in an atom?NucleusNeutrons (no charge) and protons (+ charge)

Mass # = # neutrons + # protons

Mass # = 6.941 ~ 7

# Neutrons

# neutrons = mass # - atomic #(neutrons + protons) (protons)

OR(electrons)

ExampleWhat 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 = 7 - 3 = 4

Now You TryFind the atomic #, mass #, # protons, electrons, and

neutrons

1. Beryllium

2. Neon

3. Sodium

Beryllium = Be

1. Atomic # = 4

2. Mass # = 9.0122 ~ 9

3. # protons = 4

4. # electrons = 4

5. # neutrons = 9 – 4 = 5

Now You TryFind the atomic #, mass #, #

protons, electrons, and neutrons1. Beryllium2. Neon3. Sodium

Neon = Ne1. Atomic # = 102. Mass # = 20.179 ~

203. # protons = 104. # electrons = 105. # neutrons = 20 -10

= 10

Now You TryFind the atomic #, mass #, #

protons, electrons, and neutrons1. Beryllium2. Neon3. Sodium

Sodium = Na1. Atomic # = 112. Mass # = 22.990 ~

233. # protons = 114. # electrons = 115. # neutrons = 23 -11

= 12

Shorthand Ways of Writing

108Ag

47

mass #

atomic #

# protons = 47# electrons = 47# neutrons = 108 - 47 = 61

Shorthand Ways of Writing

Carbon - 12

element name

mass #(bottom #) rounded to whole #OR (average atomic mass) rounded to whole #)

IsotopesIsotopes = Atoms with DIFFERENT # of neutronsDifferent mass # = # proton + # neutronSame # electrons and protons

Mass # = 10p + 10n = 20Neon-2020Ne10

Mass # = 10p + 11n = 20Neon-2121Ne10

Mass # = 10p + 12n = 20Neon-2222Ne10

Now You Try

Find the following:

a) Atomic #

b) Mass #

c) # protons

d) # electrons

e) # 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 atomsCarbon-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

AbundanceAtomic mass

Carbon-12 98.89% 12.000 amu

Carbon-13 1.11% 13.003 amu

Atomic mass carbon = (atomic mass carbon-12) + (atomic mass carbon-13)

Atomic mass carbon = 11.8668 + 0.1443333 = 12.0111333 ~ 12.011 amu

Isotope Natural Abundance

Atomic mass

Carbon-12 98.89% 12.000 amu

Carbon-13 1.11% 13.003 amu

Now You TryCalculate the atomic mass for

the following.1. Chlorine1. Chlorine-35

75.77% 34.969 amu

2. Chlorine-37 24.23% 36.966 amu

2. Oxygen1. Oxygen-16

99.759% 15.995 amu

2. Oxygen-17 0.037% 16.995 amu

3. Oxygen-181. 0.204%2. 17.999 amu

1. Chlorine = 35.453 amu

2. Oxygen = 15.999 amu