CHEMISTRY The Central Science 10th Edition

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CHEMISTRY The Central Science 10th Edition
Chapter 2Atoms, Molecules, and Ions
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The Atomic Theory of Matter

• John Dalton
• Each element is composed of atoms
• All atoms of an element are identical.
• In chemical reactions, the atoms are not changed
• Compounds are formed when atoms of more than one
  element combine.
• Law of Multiple Proportions When two elements
  form different compounds, the mass ratio of the
  elements in one compound is related to the mass
  ratio in the other by a small whole number.

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Self study The history of the development of
atomic theory10th Ed pp. 38-43
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The Modern View of Atomic Structure

• The atom consists of positive, negative, and
  neutral entities
• protons, p
• electrons, e-
• neutrons, no
• Protons and neutrons are located in the nucleus
  of the atom.
• The nucleus is very small compared to the size of
  the atom, but carries most of the mass of the
  atom.

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1 Å 10-10 m 100 pm
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• All atoms of the same element have the same
  number of protons.
• There can be a variable number of neutrons for
  the same number of protons. Isotopes have the
  same number of protons but different numbers of
  neutrons.

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• Electrons are located outside the nucleus. Most
  of the volume of the atom is due to electrons.

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Example
Assume that the diameter of a H atom is 2 Å.
What percentage of the volume of H is taken up by
the nucleus? If the mass of the proton is 1.0073
amu, what is the density of the H atom nucleus?
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Example
Cube of gold 1.00 cm on the side has a mass of
19.3 g. A gold atom has a mass of 197.0 amu.
How many atoms in the cube? Gold atoms
adopt an hexagonal close packed structure.
Estimate the diameter (in Å) of a gold atom.
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• Isotopes, Atomic Numbers, and Mass Numbers
• Atomic number (Z) number of protons in the
  nucleus
• All atoms of the same element have the same
  atomic number
• Mass number (A) total number of nucleons in the
  nucleus (i.e., protons and neutrons).
• Isotopes have the same Z but different A.
• By convention, for element X, we write

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127 nucleons
127 50 77 neutrons
50 protons
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Often write just as
because we know from the periodic table that Z50
for Sn
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Know the names and symbols of all elements up to
Z 89, excluding f block
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• The periodic table is arranged in increasing
  values of Z

Know the names and symbols of all elements up to
Z 89, excluding f block
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Identify
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Identify
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• The Atomic Mass Scale
• Atoms have very small masses
• 1H has a mass 1.6735 ? 10-24 g 16O has a mass of
  2.6560 ? 10-23 g.
• Definition mass of 12C exactly 12 atomic mass
  units (amu).
• Hence
• 1 amu 1.66054 x 10-24 g
• 1 g 6.02214 x 1023 amu

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• Atomic Weights
• Masses of all atoms expressed relative to the
  mass of 12C.
• Such masses are called relative atomic masses or
  atomic weights. Symbol Ar

Example Ar of 19F 19.00. Hence a 19F atom has
19.00/12.00 1.58 the mass of 12C
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• Accurate values of atomic weights determined by
  mass spectrometry.

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• Accurate values of atomic weights determined by
  mass spectrometry.

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• Accurate values of atomic weights determined by
  mass spectrometry.
• Atomic weights listed in the Periodic Table are
  weighted averages of the atomic weights of the
  isotopes of the elements.

Example Chlorine is a mixture of two isotopes.
75.77 consists of 35Cl which has an atomic
weight of 34.9689 amu 24.23 is due to 37Cl,
36.9659 amu. What is the atomic weight of
chlorine?
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Since atomic weights compare the mass of an atom
to the mass of 12C, atomic weight or relative
atomic mass has no units.
Atomic weights are listed in the periodic table
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• The Periodic Table is used to organize the 114
  elements in a meaningful way.
• As a consequence of this organization, there are
  periodic properties associated with the periodic
  table.

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• Columns in the periodic table are called groups
  (numbered from 1A to 8A or 1 to 18).

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• Rows in the periodic table are called periods.

Period 1 or Row 1
Period 2 or Row 2
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• Metals are located on the left hand side of the
  periodic table (most of the elements are metals).

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• Non-metals are located in the top right hand side
  of the periodic table.

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• Metalloids have some metallic and some
  non-metallic properties. They are located at the
  interface between the metals and non-metals.

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Example
Ar H Ga Al Ca Br Ge K O
Identify

• Alkaline earth metal
• A metal that forms a 3 ion
• An element with chemical properties similar to
  Al
• A halogen
• A metal that readily loses one electron
• A non-metal that forms a -2 ion

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Molecules and Molecular Compounds
Molecules and Chemical Formulas

• Molecules are assemblies of two or more atoms
  bonded together.

• Noble gases exist as monoatomic species He, Ar,
  Kr, etc.

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Molecules and Chemical Formulas

• Molecules are assemblies of two or more atoms
  bonded together.

• Each molecule has a chemical formula.
• The chemical formula indicates
• which atoms are found in the molecule, and
• in what proportion they are found.

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Molecules and Chemical Formulas

• Molecules are assemblies of two or more atoms
  bonded together.

• Each molecule has a chemical formula

• Compounds formed from molecules are molecular
  compounds.

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Molecules and Chemical Formulas

• Molecules are assemblies of two or more atoms
  bonded together.

• Each molecule has a chemical formula.

• Compounds formed from molecules are molecular
  compounds.

• Molecules that contain only two atoms bonded
  together are called diatomic molecules.

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• Molecules that contain only two atoms bonded
  together are called diatomic molecules.

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Molecular and Empirical Formulas

• Molecular formulas give the actual numbers and
  types of atoms in a molecule.
• Examples H2O, CO2, CO, CH4, H2O2, O2, O3, and
  C2H4.

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Molecular and Empirical Formulas

• Empirical formulas give the relative numbers and
  types of atoms in a molecule
• i.e., they give the lowest whole number ratio of
  atoms in a molecule.

Molecular formula H2O2
Empirical formula HO
Molecular formula O3
Empirical formula O
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• Molecules occupy three dimensional space.

• However, we often represent them in two
  dimensions.
• The structural formula gives the connectivity
  between individual atoms in the molecule.

Methane, CH4
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• Molecules occupy three dimensional space.

• However, we often represent them in two
  dimensions.
• The structural formula gives the connectivity
  between individual atoms in the molecule.

• The structural formula gives no information about
  the spatial arrangements of the atoms in a
  molecule

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• A perspective drawing shows the spatial
  relationships between the atoms of a molecule.

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• A perspective drawing shows the spatial
  relationships between the atoms of a molecule.

• A ball-and-stick model is sometime used.

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• A perspective drawing shows the spatial
  relationships between the atoms of a molecule.

• A ball-and-stick model is sometime used.

• The most accurate representation of the shape and
  volume of a molecule is given by a space-filling
  model.

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Applies equally to large molecules such as
proteins
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Applies equally to large molecules such as
proteins
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Applies equally to large molecules such as
proteins
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Applies equally to large molecules such as
proteins
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Ions and Ionic Compounds

• When an atom or molecule loses electrons, it
  becomes positively charged.
• For example, when Na loses an electron it becomes
  Na.
• Positively charged ions are called cations.

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• When an atom or molecule gains electrons, it
  becomes negatively charged.
• - For example, when Cl gains an electron it
  becomes Cl-.
• Negatively charged ions are called anions.

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• An atom or molecule can gain or lose more than
  one electron.

SO42- PO43- Cu2 Co(H2O)63
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Metal atoms tend to lose electrons to become
cations non-metal ions tend to gain electrons to
form anions.
Na Mg2 O2- S2- Cl- Br-
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• Predicting Ionic Charge

The number of electrons an atom of an element
gains or loses is related to the position of the
element in the periodic table.
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Ionic Compounds
Many chemical compounds do not consist of
discrete molecules, but of ions bound together by
coulombic attraction in a crystal lattice.
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To form NaCl
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To form NaCl

• The neutral sodium atom, Na, loses an electron to
  become a cation Na.
• The electron is transferred to a chlorine atom,
  Cl, which then becomes an anion Cl-.
• The Na and Cl- ions attract each other to form
  an ionic NaCl lattice which crystallizes.

Ionic compounds are represented by their
empirical formula, such as NaCl for sodium
chloride
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Glucose is a molecule with chemical formula
C6H12O6
This is its molecular formula
The empirical formula gives the simplest
combining ratio of the atoms in the molecule
The empirical formula of glucose is
CH2O
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If a species exists as well-defined discrete
molecules, then we use the molecular and not the
empirical formula
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For many compounds the empirical and molecular
formulas are identical
NH3 N2O5 H2SO4 ..
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• Polymer species that exist as giant molecule
  such as natural polymers (silk, lignin, keratin)
  or synthetic polymers (PVC, nylon, polyesters)

• Substances that exist in large extended networks
  such as ionic solids (NaCl, KNO3) or covalent
  networks (diamond, graphite)

are represented by their empirical formulas
C2H3Cl NaCl C
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What can we say about
AlCl3 N2O4
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Example Magnesium nitride

• Mg loses two electrons to become Mg2
• Nitrogen gains three electrons to become N3-
• Overall, ionic compounds are neutral species
• Lowest common multiple of 2 and 3 is 6
• Therefore, for every 6 electrons lost by Mg (2 e
  ? 3 atoms), 6 are gained by N (3 e ? 2 atoms)
• The empirical formula is Mg3N2.

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Self-study Naming of inorganic
compounds 10th Ed pp. 60-67
Learn well Tables 2.4 (p. 62) and 2.5 (p. 64)
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Example

• Give the empirical formula of the compound formed
  between In3 and
• phosphate
• sulfate
• nitrate

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End of Chapter 2