modern chemistry chapter 3 atoms: the building block of matter
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Modern Chemistry Chapter 3 Atoms: The Building Block of Matter. Mass number nuclide Atomic mass unit Average atomic mass Mole Avogadro’s number Molar mass. Chapter Vocabulary. Law of conservation of mass Law of definite proportions Law of multiple proportions Atom Nuclear forces - PowerPoint PPT PresentationTRANSCRIPT
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Modern ChemistryChapter 3Atoms:
The Building Block of Matter
2
Ch
ap
ter
Voca
bu
lary
Law of conservation of mass
Law of definite proportions
Law of multiple proportions
AtomNuclear forcesAtomic numberIsotope
Mass numbernuclideAtomic mass unitAverage atomic
massMoleAvogadro’s
number Molar mass
Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Section 1
Atoms: From Philosophical
Idea to
Scientific Theory
Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Foundation of Chemical Atomic Theory
• Law of Conservation of Mass– Mass is neither created nor destroyed
during ordinary chemical reactions or physical changes
Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Law of Conservation of Mass Image
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Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Law of Conservation of Mass Image
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Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Foundation of Chemical Atomic Theory
• Law of Definite Proportions– A chemical compound contains the
same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the compound.
Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Foundation of Chemical Atomic Theory
• Law of Multiple Proportions– If two or more different compounds
are composed of the same two elements then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.
Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Law of Multiple Proportions Image
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Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Dalton’s Atomic Theory
1. All matter is composed
of extremely small
particles called atoms
Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Dalton’s Atomic Theory
2. Atoms of a given
element are identical in
size, mass and other
properties; atoms of
different elements differ
in size, mass and other
properties.
Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Dalton’s Atomic Theory
3. Atoms cannot be
subdivided, created or
destroyed.
Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Dalton’s Atomic Theory
4. Atoms of different
elements combine in
simple whole-number
ratios to form chemical
compounds.
Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Dalton’s Atomic Theory
5. In chemical reactions,
atoms are combined,
separated or
rearranged.
Chapter 3 Section 1 Atoms: Ideas to Theory pages 67-71
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Modern Atomic Theory
Leucippus
Democritus
Atomic Theory Tested by experiment and
modified with new discoveries and experiments
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Section 2
The Structure of the Atom
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Discovery of the Electron• Cathode Ray Tube Experiment -
Thompson• Observations
– Cathode Rays are deflected a magnetic field.
– Cathode rays are deflected from a negatively charged object.
– Charge to mass ratio is always the same for the cathode rays.
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Discovery of the Electron• Cathode Ray Tube
Experiment - Thompson• Conclusion
– Cathode rays are composed of negatively charged particles
– Named “electrons”
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Discovery of the Electron• Oil Drop Experiment - Millikan
– Measured the charge of the electron– Calculated the mass of an electron
•9.109 x 10-31 kg
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Discovery of the Electron• Inferences
–Atoms are neutral, so there must be a positive charge.
–Electrons are small, so there must be other particles.
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Discovery of the Electron• Plum Pudding Model
–Negative electrons were spread evenly throughout the positive charge.
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Discovery of the Atomic Nucleus
• Gold Foil Experiment – Rutherford et. al– Hypothesis: Alpha particles would
pass through with slight deflection.– Observation: 1 in 8000 particles were
deflected back to the source.– Conclusion: The atom contains a
small densely packed bundle of matter with a positive charge
– Named the “nucleus”
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Gold Foil Experiment Imagep
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Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Discovery of the Atomic Nucleus
Relative size of the nucleus
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Composition of The Atomic Nucleus
• Nuclei contain protons and neutrons• Neutral because number of protons
equal number of electrons• Each element has a different number of
protons in their nucleus – The number of protons determines
the atom’s identity• Nuclear forces hold protons & neutrons
together
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Properties of Subatomic Particles
p.
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Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Gold Foil Experiment Photo
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Gold Foil Experiment Photo
Chapter 3 Section 2 The Structure of the Atom pages 72-76
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Thompson and Rutherford Photo
Chapter 3 Section 3 Counting Atoms pages 77-87
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Section 3
Counting Atoms
Chapter 3 Section 3 Counting Atoms pages 77-87
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Atomic Number• The number of protons of each
atom of that element• Identifies the element
Chapter 3 Section 3 Counting Atoms pages 77-87
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Isotopes• Atoms of the same element that
have different masses• Isotopes of hydrogen
– Protium 1p+ 0n0
– Deuterium 1p+ 1n0
– Tritium 1p+ 2n0
• Isotopes do not differ significantly in their chemical behavior
Chapter 3 Section 3 Counting Atoms pages 77-87
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Mass Numbers• Mass numbers = # of p+ + # of n0
of a specific isotope• Examples
– Protium 1p+ + 0n0 = 1– Deuterium 1p+ + 1n0 = 2– Tritium 1p+ + 2n0 = 3
Chapter 3 Section 3 Counting Atoms pages 77-87
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Designating Isotopes• Hyphen notation
– name of element – mass number– Hydrogen – 3
• Nuclear symbol
mass number
atomic number
Chapter 3 Section 3 Counting Atoms pages 77-87
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Number of neutrons in an atom
neutrons = mass number – atomic number
Problem page 77
How many p+, e- and n0 are there in an atom of chlorine-37? 17 p+ 17e- 20n0 (37-17)
Practice Problems page 78 #1-3Nuclide – a general term for a specific
isotope of an element
Chapter 3 Section 3 Counting Atoms pages 77-87
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Relative Atomic Mass• One atom, carbon-12, is set as a
standard• All masses are expressed in
relation to this standard• 1 atomic mass unit = 1/12 the
mass of a carbon-12 atom
Chapter 3 Section 3 Counting Atoms pages 77-87
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Relative Atomic Mass• Examples
– Hydrogen – 1 = 1.007825 amu– Oxygen – 16 = 15.994915 amu– Magnesium – 24 = 23.985042 amu
• p+ = 1.007276 amu, n0 = 1.008665 amu, e- = 0.0005486 amu
• Relative mass and mass number are close in value but not the same
Chapter 3 Section 3 Counting Atoms pages 77-87
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Average Atomic Mass• The weighted average of the atomic
masses of naturally occurring isotopes of an element
• AM = (mass isotope x abundance)+(mass isotope x abundance)+...
• Example– Copper
Cu-63: .6915 x 62.93 amu = 43.52Cu-65: .3085 x 64.93 amu = 20.03 63.55 amu
percentrelative mass
Chapter 3 Section 3 Counting Atoms pages 77-87
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The Mole• An amount of a substance that
contains as many particles as there are atoms in exactly 12 g carbon-12.
• Similar to a dozen or a pair or a gross
• 6.022 x 1023 carbon-12 atoms = 12 grams of carbon-12
• Avogadro’s number = 6.022 x 1023 particles
Chapter 3 Section 3 Counting Atoms pages 77-87
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Molar mass• The mass of one mole of a pure
substance • Unit = g/mol• On the periodic table, use 4 sig.
figs.
Chapter 3 Section 3 Counting Atoms pages 77-87
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Gram-Mole Conversions• The conversion factor for gram-
mole conversion is molar mass.
• What is the mass, in grams, of 3.50 moles of Cu?– 222 grams Cu
ORg
molg
mol
Chapter 3 Section 3 Counting Atoms pages 77-87
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Practice Problems page 851. What is the mass in grams of 2.25
mol of the element iron?2. What is the mass in grams of 0.357
mol of the element potassium?3. What is the mass in grams of
0.0135 mol of the element sodium?4. What is the mass in grams of 16.3
mol of the element nickel?
p. 8
5
126 g Fe
14.7 g K
0.310 g Na
957 g Ni
Chapter 3 Section 3 Counting Atoms pages 77-87
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Chapter 3 Section 3 Counting Atoms pages 77-87
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Gram-Mole Conversions• The conversion factor for gram-
mole conversion is molar mass.
• A Chemist produced 11.9 g of Al. How many moles of Al were produced?– 0.411 moles Al
ORg
molg
mol
Chapter 3 Section 3 Counting Atoms pages 77-87
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Practice Problems page 831. How many moles of calcium are in
5.00 g of calcium?2. How many moles of gold are in 3.60
x 10-5 g of gold?3. How many moles of zinc are in
0.535 g of zinc?
p. 8
5
0.125 mol Ca
1.83 x 10-7 mol Au
8.18 x 10-3 mol Zn
Chapter 3 Section 3 Counting Atoms pages 77-87
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Conversions with Avogadro’s Number
• The conversion factor for particle-mole conversion is Avogadro’s number.
• How many moles of silver are in 3.01 x 1023 atoms of silver– 0.500 moles Ag
OR6.022x1023atoms
1 mol 6.022x1023atoms
1 mol
Chapter 3 Section 3 Counting Atoms pages 77-87
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Practice Problems page 841. How many moles of lead are 1.50 x
1012 atoms of lead?2. How many moles of tin are in 2500
atoms of tin?3. How many atoms of aluminum are
in 2.75 mol of aluminum?
p. x
x
2.49 x 10-12 mol Pb
4.2 x 10-21 mol Sn
1.66 x 1024 atoms Al
Chapter 3 Section 3 Counting Atoms pages 77-87
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Conversions with Avogadro’s Number
• The conversion factor for particle-mole conversion is Avogadro’s number.
• What is the mass, in grams, of 1.20x1018 atoms of Cu?– 1.27 x 10-4 g Cu
OR6.022x1023atoms
1 mol 6.022x1023atoms
1 mol
Chapter 3 Section 3 Counting Atoms pages 77-87
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Practice Problems page 851. What is the mass in grams of 7.5 x
1015 atoms of nickel?2. How many atoms of sulfur are in
4.00 g of sulfur?3. What mass of gold contains the
same number of atoms as 9.0 g of aluminum?
p. x
x
7.3 x 10-7 g Ni
7.51 x 1022 atoms S
66 g Au
Chapter 3 Section 3 Counting Atoms pages 77-87
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