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3-3:
Counting Atoms
Beaker Breaker
1. What was the name of Rutherford’s
experiment?
2. What did Rutherford’s experiment
discover?
3. My atomic number is 36..who am I?
Objectives
• Explain isotopes
• Define mass # and atomic #
• Given the identity of a nuclide, determine
its # protons, neutrons & electrons
What is the same for all atoms on
an element ?
• # protons
• Atomic number, Z = # protons in the
nucleus of each atom of that element
ISOTOPES
• Atoms of the same element that differ in
mass
• Have the same # protons but
different # neutrons
Isotopes (con’t)
• Atomic #
= # protons
• # protons determines the identity of the
element
• # neutrons determines the isotope of the
element
• (Another revision to Dalton’s Theory)
• Although isotopes differ in mass, they
do NOT significantly differ in their
chemical properties
Beaker Breaker
1.
The_____________of an element is the number of
protons in the nucleus of each atom of that element.
2.
______________are atoms of the same element that
have different masses.
3.________________number is the total number of protons
and neutrons in the nucleus of an isotope.
Mass Number
• Mass number: total number of
protons and neutrons in the
nucleus of an isotope
# protons (At. #)
+ # neutrons
Mass #
• NUCLIDE: particular kind of atom
containing a definite number of protons
and neutrons
–ex. Carbon-14
Mass #, A - total # nucleons (particles that
make up the nucleus --> protons and
neutrons)
How many neutrons are in
carbon-14?
# protons (At. #)
+ # neutrons
Mass #
If:
6
+ ?
14
then:
How can you determine the #
neutrons in an isotope?
Mass #
- Atomic #
# neutrons
# protons + # neutrons
- # protons
# neutrons
Designating Isotopes
• Carbon–14
or……..
(name mass #)
14
mass #
6
atomic #.
• C
element symbol.
Radium-226
•
•
•
•
•
ID the following:
# protons
# neutrons
# electrons
atomic symbol
Radium-226
•
•
•
•
•
•
•
ID the following:
# protons
Atomic # = 88 88 protons
# neutrons
226-88=138
# electrons
# protons = # electrons (neutral) 88 electrons
• atomic symbol
•
226Ra
88
Beaker Breaker
1.
How many protons, electrons, and neutrons are in an atom of
bromine-80?
2.
Write the nuclear symbol for carbon-13
3.
Write the hyphen notation for the element that contains 15 electrons
and 15 neutrons.
Homework
Name
At. SymbolAt.# Mass # # neut. # protons
11
136
Lithium-9
Ba
23
56
6
Name
At. SymbolAt.# Mass # # neut. # protons
Sodium-23
23
Barium-136
136
Lithium-9
Na
9
11
Ba
Li
3
56
11
23
12
11
56
136
80
56
3
9
6
3
Atomic masses are VERY, VERY
small…..too small to be measured in grams!
We need another way to express “how
much”
• Electron = 9.10953 x 10-28 g
• Proton = 1.67265 x 10-24 g
• Neutron = 1.67495 x 10-24g
Scientists use a relative scale to
describe atomic mass – Atomic
Mass Units
• Carbon-12 nuclide is the standard
• Carbon-12 = 12 atomic mass units
(amu)
• The mass of all nuclides is
determined by comparing them to
carbon-12
What is the value of 1 amu ??
• If 12 amu = 1 carbon-12 atom, then…
• 1 amu = 1/12 the mass of a carbon-12 atom
• Since H = 1/12 the mass of carbon-12, then..
• H = 1/12 ( 12 amu) = 1 amu
• O = 4/3 mass of carbon-12
• = 4/3 (12amu) = 16 amu
proton = 1.007276 amu
neutron = 1.008665 amu
electron = 0.0005486 amu
If we round…
proton = 1 amu
neutron = 1 amu
electron = 0 amu
Atomic Mass
• Sum of subatomic masses in a atom
– Carbon-12:
• 6 protons = 6 ( 1 amu) = 6 amu
• 6 neutrons = 6 ( 1 amu) = 6 amu
• 6 electrons = 6 ( 0 amu) = 0 amu
12 amu
•
•
•
•
Predict the atomic mass of oxygen-16
8 protons + 8 neutrons + 8 electrons
= 8 amu + 8 amu
+ 0 amu
= 16 amu
• How does this compare with the
atomic mass value on Periodic Table?
• Predict the atomic mass of uranium-234
• 92 protons + 142 neutrons + 92
electrons
• = 92 amu + 142 amu
+ 0 amu
• = 234 amu
• How does this compare with the atomic
mass value on Periodic Table?
• 238 !!…why is it different?
Average Atomic Mass
• Weighted average of the atomic
masses of the naturally
occurring isotopes of an
element
IF 40.% of the students living in
Hershey have 2 telephones while
60.% of the students have 4 phones,
what is the average # phones in
Hershey homes?
• (0.40 x 2 phones) + (0.60 x 4 phones)
• 3.2 phones
• “weighted” average
What is the aver. atomic mass of
the chlorine?
Isotope
Isotope Mass (amu) % Abundance
Chlorine-35
34.96885
75.771
Chlorine-37
36.96590
24.229
• Average Atomic Mass =
• (isotope mass)(relative abundance[dec]) +
(isotope mass)(relative abundance[dec])
• (0.75771)(34.96885amu) + (0.24229)(36.96590amu)
• = 35.453
amu
Which isotope of hydrogen is the
most abundant…?
hydrogen-1
hydrogen-2
hydrogen-3
• Hydrogen-1 (1.0079 = aver. atomic
mass on chart)
Complete the following:
Beaker Breaker
(not in packet)
Isotope
# protons
#electrons
#neutron
Oxygen-16
29
Uranium-238
34
Complete the following:
Isotope
# protons
#electrons
#neutron
Oxygen-16
8
8
8
Copper-63
29
29
34
92
92
146
Uranium-238
Objectives
• Define MOLE in terms of Avogadro’s #
• Define MOLE in terms of molar mass
• Use FLM to convert between grams,
moles and # atoms/molecules
Relating MASS to # ATOMS
The Mole (mol)
• Amount of substance that contains as many
particles as there are atoms in exactly 12 g of
carbon-12 (Avogadros #)
• Experimentally determined to 6.0221367 x 1023
atoms
23
6.022 x 10
“Mole
Things” Conversions
How many atoms are in 0.43
moles of copper?
• 0.43 mol Cu 6.02 x 1023 atoms Cu
1
1 mol Cu
• 2.6 x 1023 atoms of Cu
=
How many moles are in
1.4 x 1022 atoms of aluminum?
• 1.4 x 1022 atoms Al
1
• = 0.023 mol Al
1 mole Al
6.02 x 1023 atoms
Beaker Breaker
•
Calculate the number of molecules in
1.058mole of H2O?
Molar Mass
• Mass of 1 mole of a pure substance
• Numerically equal to the atomic mass but
expressed in GRAMS
• What is the molar mass of the following:
• Potassium ?
• 39.098 g (or 39.098 g/mol)
Nickel ?
• 58.693 g (or 58.693 g/mol)
• What is the atomic mass of the following:
• Potassium ?
• 39.098 amu
Nickel ?
• 58.693 amu
Gram-
Mole Conversions
How many grams are needed to
have 0.852 moles gold?
• 0.852 mol Au 196.97 g Au
1
1 mol Au
= 168 g Au
How many moles are in 55 g of
lead?
• 55 g Pb 1 mol Pb
1
207.2 g Pb
• = 0.26 moles Pb
How many moles are in
86.1 g sodium?
• 86.1 g ? mole Na =
1
? g
•
•
86.1 g 1 mole Na =
1
22.99g
3.74 moles Na
How many atoms would be in
12.0 grams of carbon-12 ?
• If …atomic mass of carbon-12 = 12.0 amu
(chart value)
• Then…12.0 g C = 1 mole (molar mass)
• And since…..1 mole = 6.022 x 1023 atoms
• Then…12.0 g carbon contains 6.02 x 1023 C atoms
Beaker Breaker
1. How many moles are there in 5.04x103
atoms of Cu?
Gram
#Atoms Conversions
How many atoms are in 54.21 g
potassium?
• 54.21 g K 1 mole K
1
• =
39.098g K
6.022 x 1023 atoms K
1 mole K
8.350 x 1023 atoms K
How many grams are in
5.75 x 1021 atoms of Mg?
• 5.75 x 1021 atoms
1
1 mole
24.305 g
6.022 x 1023 atoms 1 mole
• 0.232 grams Mg
Beaker Breaker
• How many grams are there in 780atoms of
nickel?
• MOLE definition movie
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