Atoms, Molecules and Ions

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Atoms, Molecules and Ions

• Daltons Atomic Theory
• Atomic Structure
• Atomic Mass
• Chemical Formulas
• Chapters 2.1-2.8, 3.2-3.3, 3.11-3.12 (McM)
• Chapters 2.1-2.5, 3.1 (Silberberg)

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Goals Objectives

• The student will understand the characteristics
  of the three types of matter elements,
  compounds, and mixtures. (2.1)
• The student will understand the significance of
  the three mass laws conservation of mass,
  definite composition and multiple proportions.
  (2.2)

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Goals Objectives

• The student will understand the postulates of
  Daltons atomic theory and how it explains the
  mass laws. (2.3)
• The student will understand the major
  contributions of experiments by Thomson,
  Millikan, and Rutherford concerning the atomic
  structure. (2.4)

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Goals Objectives

• The student will understand the structure of the
  atom along with the characteristics of the
  proton, neutron, and electron and the importance
  of isotopes. (2.5)
• The student will understand the meaning and
  usefulness of the mole. (3.1)

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Goals Objectives

• The student will understand the relationship
  between the formula mass and molar mass. (3.1)
• The student will understand the relationship
  among the amount of substance (in moles), mass
  (in grams), and the number of chemical atoms.
  (3.1)

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Goals Objectives

• The student will understand the information in a
  chemical formula. (3.1)

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Master these Skills

• Distinguish between elements, compounds and
  mixtures at the atomic scale. (SP 2.1)
• Using the mass ratio of an element to a compound
  to find the mass of an element in a compound. (SP
  2.2)
• Visualizing the mass laws. (SP 2.3)

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Master these Skills

• Using atomic notation to express the subatomic
  makeup of an isotope. (SP 2.4)
• Calculating an atomic mass from isotopic
  composition. (SP 2.5)
• Calculating the molar mass of any substance.
  (3.1 SP 3.3 and 3.4)

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Master these Skills

• Converting between amount of substance (in
  moles), mass (in grams), and the number of atoms.
  (SP 3.1-3.3)

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Matter

• A scheme for the classification of matter

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Definitions for Components of Matter
Element - the simplest type of substance with
unique physical and chemical properties. An
element consists of only one type of atom. It
cannot be broken down into any simpler substances
by physical or chemical means.
Molecule - a structure that consists of two or
more atoms that are chemically bound together and
thus behaves as an independent unit.
Figure 2.1
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Definitions for Components of Matter
Compound - a substance composed of two or more
elements which are chemically combined.
Figure 2.1
Mixture - a group of two or more elements and/or
compounds that are physically intermingled.
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Daltons Atomic Theory
The Postulates
1. All matter consists of atoms.
2. Atoms of one element cannot be converted into
atoms of another element.
3. Atoms of an element are identical in mass and
other properties and are different from atoms of
any other element.
4. Compounds result from the chemical combination
of a specific ratio of atoms of different
elements.
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Daltons Atomic Theory
explains the mass laws
Mass conservation
Atoms cannot be created or destroyed
postulate 1
or converted into other types of atoms.
postulate 2
Since every atom has a fixed mass,
postulate 3
during a chemical reaction atoms are combined
differently and therefore there is no mass change
overall.
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Daltons Atomic Theory
explains the mass laws
Definite composition
Atoms are combined in compounds in specific ratios
postulate 3
and each atom has a specific mass.
postulate 4
So each element has a fixed fraction of the total
mass in a compound.
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Daltons Atomic Theory
explains the mass laws
Multiple proportions
Atoms of an element have the same mass
postulate 3
and atoms are indivisible.
postulate 1
So when different numbers of atoms of elements
combine, they must do so in ratios of small,
whole numbers.
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The Structure of the Atom

• Fundamental Particles in Atoms
• Particle Mass(amu) Charge
• electron 0.00054858 -1
• proton 1.0073 1
• neutron 1.0087 0

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The Structure of the Atom

• Electrons

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Figure 2.5
Experiments to determine the properties of
cathode rays.
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Experiments to Determine the Properties of
Cathode Rays
CONCLUSION
OBSERVATION
1. Ray bends in magnetic field.
2. Ray bends towards positive plate in electric
field.
consists of charged particles
consists of negative particles
3. Ray is identical for any cathode.
particles found in all matter
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Millikans oil-drop experiment for measuring an
electrons charge.
Figure 2.6
(1909)
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Millikan used his findings to also calculate the
mass of an electron.
(-5.686x10-12 kg/C)
X
(-1.602x10-19C)
9.109x10-31kg 9.109x10-28g
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Rutherfords a-scattering experiment and
discovery of the atomic nucleus.
Figure 2.7
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General features of the atom today.
Figure 2.8

• The atom is an electrically neutral, spherical
  entity composed of a positively charged central
  nucleus surrounded by one or more negatively
  charge electrons.

• The atomic nucleus consists of protons and
  neutrons.

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Properties of the Three Key Subatomic Particles
Table 2.2
Charge
Mass
The coulomb (C) is the SI unit of charge.
The atomic mass unit (amu) equals 1.66054x10-24
g.
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The Modern Reassessment of the Atomic Theory
1. All matter is composed of atoms. The atom is
the smallest body that retains the unique
identity of the element. 2. Atoms of one element
cannot be converted into atoms of another element
in a chemical reaction. Elements can only be
converted into other elements in nuclear
reactions. 3. All atoms of an element have the
same number of protons and electrons, which
determines the chemical behavior of the element.
Isotopes of an element differ in the number of
neutrons, and thus in mass number. A sample of
the element is treated as though its atoms have
an average mass. 4. Compounds are formed by the
chemical combination of two or more elements in
specific ratios.
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Atomic Symbols, Isotopes, Numbers
A
X
The Symbol of the Atom or Isotope
Z
X Atomic symbol of the element
A mass number A Z N
Z atomic number (the number
of protons in the nucleus)
N number of neutrons in the nucleus
Isotope atoms of an element with the same
number of protons, but a different number of
neutrons
Figure 2.9
See Laboratory Tools
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Tools of the Laboratory
The Mass Spectrometer and Its Data
Figure B2.2
return to previous slide
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Isotopes and Neutrons

• atoms of the same element having different atomic
  mass numbers

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The Complete Symbol

• Competency III-1
• MZX where
• M atomic mass number(p n)
• Z atomic number (p)
• electrons in a neutral atom
• Number of neutrons M - Z
• 73Li p ___ e ____ n ____
• 7434Se p ____ e ____ n ____

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Ions

• Charged atoms obtained by adding or removing
  electrons to an atom.
• Cations-positively charged ions
• Anions-negatively charged ions
• 3919K p ___ e ___ n ___
• 3216S-2 p ___ e ___ n ___

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Chemical Formulas

• Monoatomic elements Na, K, He
• Diatomic elements H2, O2, N2, F2, Cl2, Br2, I2
• Compounds
• HCl ______________________
• H2O______________________
• C3H8_____________________

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Atomic Weights(Masses)

• a relative scale based upon 126C having a mass of
  exactly 12 amu (atomic mass units)
• The atomic weight of an element is the weighted
  average of all the isotopes of that element.

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Sample Problem 2.3
Calculating the Atomic Mass of an Element
PLAN
We have to find the weighted average of the
isotopic masses, so we multiply each isotopic
mass by its fractional abundance and then sum
those isotopic portions.
SOLUTION
multiply by fractional abundance of each isotope
portion of atomic mass from each isotope
atomic mass
mass(g) of each isotope
add isotopic portions
mass portion from 107Ag 106.90509amu x 0.5184
55.42amu
mass portion from 109Ag 108.90476amu x 0.4816
52.45amu
atomic mass of Ag 55.42amu 52.45amu
107.87amu
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Atomic Weights(Masses)

• Naturally occurring copper consists of two
  isotopes. It is 69.1 6329Cu which has a mass of
  62.9 amu and 30.9 6529Cu which has a mass of
  64.9 amu. Determine the atomic weight of copper.

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Atomic Weights(Masses)

• Naturally occurring chromium consists of four
  isotopes. It is
• 4.31 chromium-50 ,mass 49.946amu, 83.76
  chromium-52, mass 51.941amu, 9.55 chromium
  53, mass 52.941amu 2.38 chromium 54, mass
  53.939amu.
• Determine the atomic mass of chromium.

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Atomic Masses (Weights)

• Element Atomic Weight
• H 1.0079 amu
• N 14.0067 amu
• Mg 24.3050 amu

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The Mole
mole(mol) - the amount of a substance that
contains the same number of entities as there are
atoms in exactly 12 g of carbon-12.
This amount is 6.022x1023. The number is called
Avogadros number and is abbreviated as N.
One mole (1 mol) contains 6.022x1023 entities (to
four significant figures)
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The Mole

• One mole is defined as 6.022 x 1023 objects.
  Also called Avagadros number.
• The mass of one mole of an element will be its
  atomic mass expressed in grams.

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The Mole

• Element Mass Contains Atoms
• H 1.0079g 6.022 x 1023
• N 14.0067g 6.022 x 1023
• Cl 35.453 g 6.022 x 1023

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Counting objects of fixed relative mass.
Figure 3.1
12 red marbles _at_ 7g each 84g 12 yellow marbles
_at_4g each 48g
55.85g Fe 6.022 x 1023 atoms Fe 32.07g S
6.022 x 1023 atoms S
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Figure 3.2
Oxygen 32.00 g
One mole of common substances.
Water 18.02 g
CaCO3 100.09 g
Copper 63.55 g
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Information Contained in the Chemical Formula of
Glucose C6H12O6 ( M 180.16 g/mol)
Table 3.1
Oxygen (O)
Carbon (C)
Hydrogen (H)
Atoms/molecule of compound
6 atoms
6 atoms
12 atoms
Moles of atoms/ mole of compound
6 moles of atoms
12 moles of atoms
6 moles of atoms
Atoms/mole of compound
6(6.022 x 1023) atoms
12(6.022 x 1023) atoms
6(6.022 x 1023) atoms
Mass/moleculeof compound
6(12.01 amu) 72.06 amu
12(1.008 amu) 12.10 amu
6(16.00 amu) 96.00 amu
Mass/mole of compound
96.00 g
72.06 g
12.10 g
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Interconverting Moles, Mass, and Number of
Chemical Entities
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Sample Problem 3.1
Calculating the Mass and the Number of Atoms in a
Given Number of Moles of an Element
(a) Silver (Ag) is used in jewelry and tableware
but no longer in U.S. coins. How many grams of
Ag are in 0.0342mol of Ag?
(b) Iron (Fe), the main component of steel, is
the most important metal in industrial society.
How many Fe atoms are in 95.8g of Fe?
PLAN
(a) To convert mol of Ag to g we have to use the
g Ag/mol Ag, the molar mass M.
multiply by M of Ag (107.9g/mol)
SOLUTION
3.69g Ag
0.0342mol Ag x
(b) To convert g of Fe to atoms we first have to
find the mols of Fe and then convert mols to
atoms.
PLAN
divide by M of Fe (55.85g/mol)
SOLUTION
95.8g Fe x
1.72mol Fe
multiply by 6.022x1023 atoms/mol
1.04x1024 atoms Fe
1.72mol Fe x
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Sample Problem 3.2
Calculating the Moles and Number of Formula Units
in a Given Mass of a Compound
PROBLEM
Ammonium carbonate is white solid that decomposes
with warming. Among its many uses, it is a
component of baking powder, first extinguishers,
and smelling salts. How many formula unit are in
41.6 g of ammonium carbonate?
PLAN
After writing the formula for the
compound, we find its M by adding the masses of
the elements. Convert the given mass, 41.6 g to
mols using M and then the mols to formula units
with Avogadros number.
divide by M
multiply by 6.022x1023 formula units/mol
SOLUTION
The formula is (NH4)2CO3.
M (2 x 14.01 g/mol N)(8 x 1.008 g/mol H)

(12.01 g/mol C)(3 x 16.00 g/mol O)
96.09 g/mol
41.6 g (NH4)2CO3 x
x

2.61x1023 formula units (NH4)2CO3
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Examples

• Competency I-2
• Determine the number of moles in 73.4g of Mg
• Calculate the number of atoms in 5.00 moles of
  magnesium.
• Determine the mass of a Mg atom in grams to three
  significant figures.

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Formula Weights

• The formula weight of a substance is the sum of
  the atomic weights of the atoms of each element
  in the formula.
• Determine the formula weight of propane (C3H8).
• How many molecules are present in 44.1 g of
  propane?
• Determine the number of molecules of C3H8 in
  74.6 grams of propane.

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Formula Weights

• Determine the number of (a) moles, (b) molecules,
  and (c) oxygen atoms in 60.0 g of ozone, O3.
• Determine the formula weight of Ca(NO3)2.

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Stopping Point for Quiz 2

• This quiz will cover only competencies III-1 and
  I-2.