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: total number of protons and neutrons in the nucleus of an isotope
# protons (At. #)
+ # neutrons
Mass #
Mass Number
• 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?
If: # protons (At. #) then: 6
+ # neutrons + ?
Mass # 14
How can you determine the # neutrons in an isotope?
Mass # # protons + # neutrons
- Atomic # - # protons# neutrons # neutrons
Designating Isotopes
• Carbon–14 (name mass #) or……..
• 14C mass #element symbol.
6 atomic #.
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.
Name At. SymbolAt.# Mass # # neut. # protons
11 23136 Ba 56
Lithium-9 6
Homework
Name At. SymbolAt.# Mass # # neut. # protons
Sodium-23 23 Na 11 11 23 12 11
Barium-136 136 Ba 56 56 136 80 56
Lithium-9 9 Li 3 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
If we round…proton = 1 amuneutron = 1 amuelectron = 0 amu
proton = 1.007276 amu
neutron = 1.008665 amu
electron = 0.0005486 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 34
Uranium-238
Complete the following:
Isotope # protons #electrons #neutron
Oxygen-16 8 8 8
Copper-63 29 29 34
Uranium-238
92 92 146
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
6.022 x 1023
“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 mole Al
1 6.02 x 1023 atoms
• = 0.023 mol Al
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 6.022 x 1023 atoms K
1 39.098g 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 mole 24.305 g
1 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 D:\data\0030665841\student\ch07\sec03\qc02\hc207_03_q02fs.htm
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