Modern Chemistry Chapter 3 Atoms: The Building Blocks of Matter

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Modern Chemistry Chapter 3Atoms The Building
Blocks of Matter

• law of conservation of mass- mass is neither
  created nor destroyed during ordinary chemical
  reactions or physical changes
• e.g. 20 g A 20 g B ? 40 g AB

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• 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
• e.g. If 10 grams of A combine with 20 grams of
  B to form compound AB, how many grams of B will
  be necessary to combine with 20 grams of A to
  form AB? Answer 40 grams of B.

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• 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
• e.g. H2O H2O2 or NO2 N2O5

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Daltons Atomic Theory

• In 1808, an English school teacher named John
  Dalton proposed an explanation for the law of
  conservation of mass, the law of definite
  proportions, and the law of multiple proportions.

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• Daltons Atomic Theory
• 1- All matter is composed of extremely small
  particles called atoms.
• 2- Atoms of a given element are identical in
  size, mass and other properties.
• 3- Atoms cannot be subdivided, created or
  destroyed.
• 4- Atoms of different elements combine in
  simple whole-number ratios to form chemical
  compounds.
• 5- In chemical reactions, atoms are combined,
  separated, or rearranged.

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Modern Atomic Theory

• Daltons theory was a good one, but it has since
  been modified.
• Atoms are divisible into even smaller particles.
• Atoms of a given element can have different
  masses.
• Atoms can be destroyed.
• Do Section Review 3 on page 71.

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Section review 3 page 71

• IF each compound contains 1.0 g oxygen and the
  three samples contain
• compound A K 1.22 g / 1.22 1.0
• compound B K 2.44 g / 1.22 2.0
• compound C K 4.89 g / 1.22 4.0
• 124 ratios of potassium ? multiple
  proportions

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Chapter 3 Section 2The Structure of the Atom

• atom- the smallest particle of an element that
  retains the chemical properties of that element

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• atomic nucleus- the small, densely packed,
  positively charged central portion of the atom
  that contains nearly all of its mass but nearly
  none of its volume
• neutron- The neutral particle of the nucleus of
  an atom.
• proton- The positively charged particle of the
  nucleus of an atom.
• electron cloud- The large area surrounding the
  nucleus of an atom in which the electrons are
  located.
• electron- the negatively charged particles of an
  atom

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The Discovery of Electrons

• In the late 1800s, electric current was passed
  through cathode ray tubes. It was discovered
  that the cathode ray was attracted to the
  positive pole of a magnet and repelled by the
  negative pole.
• This led to the discovery of electrons.
• In 1909, Robert Millikan measured the negative
  charge of the electron.
• From this, it was found that the mass of an
  electron is 9.109 x 10-31 kg.
• The mass of an electron is 1/1837th the mass of
  the simplest hydrogen atom.
• The negative charges of the electrons equal the
  positive charges of an atom (protons).

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The Discovery of the Atomic Nucleus

• In 1911, Ernest Rutherford, Hans Geiger, Ernest
  Marsden bombarded a thin foil of gold with
  positively charged particles called alpha
  particles. They were surprised to find that a
  few of the particles (1 in 8000) were reflected
  from the foil straight back toward their source.
  They reasoned that this must mean that there was
  a small positively charged portion of each gold
  atom.

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Composition of the Nucleus

• protons- are positively charged particles in the
  nucleus (their charge - charge of an
  electron)
• mass 1.673 x 10-27 kg or 1836/1837 the mass of
  a protium atom
• neutrons- neutral particles of the nucleus
• mass 1.675 x 10-27 kg mass of 1 electron
  1 proton

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Composition of the Nucleus

• How can the numerous positively charged protons
  exist packed into the nucleus without flying
  apart due to their like charges repelling one
  another?
• nuclear forces- are short range forces
  (proton-proton, proton-neutron,
  neutron-neutron) that hold the nuclear particles
  together.

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The Size of Atoms

• Atomic radius ranges between 40
• 270 pm (10-12 m)
• Discuss how small a picometer would be.
• Nuclear radius 0.001 pm.
• The size of the nucleus to the entire atom would
  be about the same as if you placed a dime at the
  center of the football stadium.

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Section 3.3Counting Atoms

• atomic number- is equal to the number of protons
  in the nucleus of each atom of an element
• mass number- is the number of protons plus
  neutrons in a single atom of an element.

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Counting Atoms

• isotopes- are atoms of the same element that have
  different masses due to different numbers of
  neutrons
• nuclide- is a general term for a specific isotope
  of an element
• We designate isotopes using one of two different
  designations.
• Hydrogen has three isotopes protium (m 1),
  deuterium (m 2), and tritium (m 3).
• hyphen notation H-1 H-2 H-3
• 1 2
  3
• nuclear symbol notation H H H
• 1 1 1

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Isotopes

• Do practice problems 1, 2, 3 on page 80.

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Practice problems page 80

• 1- bromine-80 ? 35 protons
• 35 electrons
• 80-35 45 neutrons
• 2- carbon-13 ? 13
• C
• 6
• 3- 15 electrons, so 15 protons element is
  phosphorus. 15 15 ? phosphorus-30

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Identifying Isotopes

• element symbol atomic mass p n0 e-
• calcium 40 ____
• uranium 92 235 ____
• uranium 238 ____
• 13 27 ____
• I-127 ____

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Relative Atomic Masses

• atomic mass unit (amu)- exactly 1/12th of the
  mass of a carbon-12 atom
• average atomic mass- is the weighted average of
  the atomic masses of the naturally occurring
  isotopes of an element
• see table 4 on page 82

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Calculating Average Atomic Mass

• We will be calculating the average mass of the
  science textbooks in the classroom. This is the
  approximate method used to determine average
  atomic mass of the isotopes of an element.
• 1- Using a bathroom scale, find the weight of
  the physics textbooks and count their number.
  What is the average weight of each book?
• 2- Find the weight of the chemistry textbooks
  and count their number. What is the average
  weight of each book?
• 3- Add the weights of the textbooks and add the
  numbers of books.
• 4- Divide the total weight by the total number
  of books to find the average weight. How does
  this compare to the average weight of each book?

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Relating Mass to Numbers of Atoms

• mole (mol)- the amount of a substance that
  contains the same number of particles as there
  are in 12 grams of carbon-12
• The concept is similar to that of a dozen.

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• Avogadros number- is equal to the number of
  particles in one mole of a substance and is equal
  to 6.022 x 1023

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Molar Mass

• molar mass- the mass of one mole of a pure
  substance
• We can find molar mass by using the average
  atomic mass found on the periodic table and
  changing the units from amu to grams.

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Mole-molar mass conversions

• mole x molar mass mass (grams)
• mass (grams) molar mass moles

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Mole Hill

• moles
• (mol)
• molar mass x molar mass
• (g/mol) (g/mol)
• mass in grams mass in grams
• (g) (g)

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Gram to Mole Conversions

• We can use conversion factors to convert between
  grams and moles.
• 2.00 mol He x 4.00 g He 8.00 g He
• 1 mol He
• 8.00 g He x 1 mol He 2.00 mol He
• 4.00 g He
• Do practice problems 1-4 and 1-3 on page 85

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Mole to Gram Conversions pg 85

1. 2.25 mol Fe x 55.85 g/mol 126 g Fe
2. 0.375 mol K x 39.10 g/mol 14.7 g K
3. .0135 mol Na x 22.99 g/mol 0.310 g Na
4. 16.3 mol Ni x 58.69 g/mol 957 g Ni

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Gram to Mole Conversions pg 85

1. 5.00 g Ca 40.08 g/mol 0.125 mol Ca
2. 3.60 x 10-5 g Au 196.97 g/mol 1.83 x 10-7 mol
   Au
3. 0.535 g Zn 65.39 g/mol 8.18 x 10-3 mol Zn

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Conversions Using Avogadros Number

• 3.01 x 1023 Ag atoms x 1 mole Ag atoms
  6.022 x 1023 Ag atoms
• 0.500 moles of Ag
• 1.20 x 108 atoms Cu x 1 mol Cu atoms x
  63.55 g
• 6.022 x 1023 Cu atoms
• Cu 1.27 x 10-14 g Cu
• Do section review problems 2-6 on page 87.

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Section review page 87

• 2a- sodium-23 ? 11 protons, 11 electrons, 12
  neutrons
• b- calcium-40 ? 20 protons, 20 electrons, 20
  neutrons
• c- copper-64 ? 29 protons, 29 electrons, 35
  neutrons
• d- silver-108 ? 47 protons, 47 electrons, 61
  neutrons
• 3a- silicon-28
• b- iron-56
• 4- potassium ? 39.10 amu 39.10 g/mol
• 5a- 2.00 mol x 14.0 g/mol 28.0 g N
• 6a- 12.15 g / 24.3 g/mol 0.50 mol Mg

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Section Review page 87

• 7- 2.06 mol Cu 222 g Ag
• Which has the larger mass?
• 2.06 mol Cu x 63.5 g/mol 130.8 g Cu
• 222 g Ag gt 130.8 g Cu
• Which beaker has the larger number of atoms?
• 222 g Ag 107.9 g/mol 2.06 mol Ag
• SINCE both beakers have the same number of
  moles, they have equal numbers of atoms.

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Chapter 3- Practice problems

• 1- U-235
• 92 electrons 92 protons
• 235-92 143 neutrons
• 2- U-238 92 electrons 92 protons
• 238-92 146 neutrons
• 3- C-14
• 6 electrons 6 protons
• 14-6 8 neutrons
• 4- I-127
• 53 electrons 53 protons
• 127-53 74 neutrons
• 5- K-41 19 electrons 19 protons 41 19
  22 neutrons

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• 6) 4.25 mol Na
• x 22.99 g/mol 97.7 g Na
• 7) 0.0013 mol Au
• x 196.97 g/mol 0.26 g Au
• 8) 111.5 mol Ca
• x 40.08 g/mol 4469 g Ca
• 9) 2.5 mol C
• x 12.01 g/mol 30 g C
• 10) 0.025 mol Ag
• x 107.87 g/mol 2.7 g Ag

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• 11) 100.3 g Ca
• 40.07 g/mol 2.503 mol Ca
• 12) 72.0 g O
• 16.00 g/mol 4.50 mol O
• 13) 0.06 g C
• 12.01 g/mol 0.005 mol C
• 14) 5.4 g Au
• 196.97 g/mol 0.027 mol Au
• 15) 3.449 x 1011 g He
• 4.00 g/mol 8.62 x 1010 mol He

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Chapter 3 Review

• Do problems 2, 6-11, 17-19, 21-24, 28 on pages
  89 90 of the textbook.
• Do the Math Tutor problems 1 2 on page 92.
• Do the Standardized Test Prep on page 93.

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Chapter 3 vocabulary

• law of conservation of mass law of definite
  proportions-
• law of multiple proportions- atom-
• atomic nucleus- neutron-
• electron cloud-
• electron- protons-
• neutrons- nuclear forces-
• atomic number- mass number-.
• isotopes- atomic mass unit
• average atomic mass- mole
• Avogadros number- molar mass-

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Chemistry Chapter 3 Test

• 30 multiple choice Questions
• definitions uses of the Laws of Conservation of
  Mass, Definite Proportions, Multiple
  Proportions
• Daltons Atomic Theory its 5 points
  modifications
• the cathode ray experiment the discovery of
  electrons
• Rutherfords experiment the discovery of the
  atomic nucleus
• definitions of proton, neutron, electron, atomic
  nucleus ( its characteristics), nuclear forces,
  atomic number, mass number, isotopes, average
  atomic mass, mole, molar mass, Avogadros
  number
• determine the number of protons, electrons,
  neutrons of an element from its atomic and mass
  numbers
• mass to mole mole to mass calculations

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Honors Chemistry Chapter 3 Test

• 50 Multiple Choice questions
• definitions implications of the Laws of
  Conservation of Mass, Definite Proportions,
  Multiple Proportions, Daltons Atomic Theory (and
  its modifications)
• implications of the cathode ray experiment the
  discovery of the electron
• Rutherfords experiment the discovery of the
  atomic nucleus
• description of an atom, atomic nucleus,
  electron cloud
• definitions implications of atom, proton,
  neutron, electron, nuclear forces, isotopes,
  average atomic mass, atomic number, mass number,
  Avogadros number, mole, molar mass
• describe the isotopes of hydrogen (protium,
  deuterium, tritium)
• determine numbers of protons, electrons
  neutrons from atomic mass numbers
• mass to mole mole to mass conversions