Chapter 2 Atoms, Molecules, and Ions

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Chapter 2Atoms, Molecules, and Ions
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LAW OF CONSERVATION OF MASS

• Antoine Lavoisier (1743-1794)
• Carefully measured and provided a quantitative
  interpretation of the chemical reaction
  associated with combustion.
• Law During a chemical change, the total mass
  remains constant.

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LAW OF DEFINITE PROPORTIONS

• Joseph Proust (1754-1826)
• Law Different samples of a pure compound always
  contain the same proportion of elements by mass.
• Also called Law of Constant Composition

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LAW OF MULTIPLE PROPORTIONS

• John Dalton (1766-1844)
• Law When two or more elements form more than
  one compound, the ratio of the masses of one
  element in these compounds for a fixed mass (i.e.
  1 gram) of the other element is a small whole
  number.

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ATOMIC THEORY OF MATTER (1808)

• John Dalton (1766-1844)
• Elements (matter) are composed of atoms
• The atoms of a given element are identical. Each
  element is characterized by the mass of its
  atoms.
• Compounds are formed when atoms of different
  elements combine with each other (Multiple
  Proportions).

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ATOMIC THEORY OF MATTER (2)

• A given compound is a chemical combination of the
  same atoms in the same relative numbers.
  (Definite Proportions).
• A chemical reaction is the rearrangement of atoms
  leading to new compounds. Atoms are neither
  destroyed nor created in a chemical reaction
  (Conservation of Mass).

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AVOGADROS HYPOTHESIS

• Amadeo Avogadro (1776-1856)
• Equal volumes of two gases at the same pressure
  and temperature contain the same number of
  particles (atoms or molecules).

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ATOMIC STRUCTURESubatomic Particles (Table 2.1)

• ELECTRON (cathode ray)
• 1899 J.J. Thomson electron charge -1 and e/m
  -1.76E8 C/g
• 1909 R. Millikan electron mass 9.11E-31 kg or
  about 1/1836 of proton or neutron mass
• PROTON 1911 Rutherford
• Positive charge, 1 Relative mass 1 amu
• NEUTRON 1932 Chadwick
• No charge, 0 Relative mass 1 amu

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Table 2.1 The Mass and Charge of the Electron,
Proton, and Neutron
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MODELS OF THE ATOM

• Thomson (Plum Pudding) Model positive mass with
  electrons embedded in it
• Rutherford Model (1911) positive charge in
  small volume with (diameter 1E-15 m) electrons
  occupying mostly empty space (d 1E-10 m)
  around the nucleus
• Bohr Atom - Chapter 7
• Quantum Mechanical Atom - Chapter 7

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Figure 2.13 a b (a) Expected Results of the
Metal Foil Experiment if Thomson's Model Were
Correct (b) Actual Results
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ATOMIC STRUCTURE

• Atomic Symbol
• Shorthand notation for element
• One or two letters on Periodic Table
• Atomic Structure
• Atomic Number (Z) protons, uniquely defines
  an atom
• Mass Number (A) protons neutrons
• If atom is neutral, Z electrons

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NUCLIDE SYMBOL

• Atomic symbol, E symbol in the middle of each
  element box on the Periodic Table.
• Z (left subscript) number on the top of each
  element box on the Periodic Table.
• A (left superscript)
• If species is an ion (has a charge), add or -
  charge (right superscript)
• AZEch 2311Na has 11 p, 11 e-, 12 no

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IONS

• A charged species with unequal numbers of protons
  and electrons.
• If protons gt electrons, the ion has a net
  positive charge and is called a cation
• If protons lt electrons, the ion has a net
  negative charge and is called a anion
• An ion may consist of an atom or a group of atoms
• 2311Na has 11 p, 10 e-, 12 no

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MOLECULES

• Molecules or compounds form when atoms are
  connected by chemical bonds in which electrons
  act as the glue between atoms.
• If electrons are shared between two atoms, the
  bond is a covalent bond. I.e., the bond between
  two non-metal atoms.
• If electrons are transferred to produce ions, the
  bond is ionic.
• Ions are charged particles which form via the
  gain (anion, commonly formed from nonmetal
  elements) or loss (cation, commonly formed from
  metal elements) of electrons.
• Oppositely charged ions attract and form an ionic
  bond.
• Type of bond between a metal and a non-metal
  atom.
• Polyatomic ions are charged groups of atoms they
  can also form ionic bonds.

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ISOTOPE

• Atoms which have the same Z (same p)but a
  different A (different n0)
• Most elements have isotopes that occur in nature
  in precise proportions (fractional abundances,
  ).
• A few elements have no naturally occurring
  isotopes.

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Figure 2.15 Two Isotopes of Sodium
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PERIODIC TABLE

• An arrangement of elements according to
  increasing atomic number which shows the periodic
  or regularly repeating nature of elemental
  properties.
• Rows periods
• Columns groups or families note similarity of
  properties
• Metals Nonmetals Semimetals
• Main group (A) Transition Metals

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Figure 2.21 The Periodic Table
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NOMENCLATURE or NAMING COMPOUNDS

• Binary Ionic Compounds
• Metal atoms tend to lose electrons and form
  cations.
• Nonmetal atoms tend to gain electrons and form
  anions.
• Use Periodic Table to determine charges and
  number of each ion in the compound. Note that
  the ionic compound must be neutral overall.
• Name cation first as element and anion second
  with ide ending.
• Binary Ionic Compound Type I (T2.3)
• Some atoms form only a single type of ion (Binary
  Ionic Cmp Type I)

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Figure 2.22 Common Cations and Anions
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NOMENCLATURE (cont)

• Binary Ionic Compound Type II (T2.4, Fig 2.22)
• Some transition metal elements form more than one
  common ion. Designate charge with Roman numeral
  (II)
• Polyatomic Ions (Table 2.5)
• Memorize
• Oxoanion nonmetal oxygen

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Table 2.6 Prefixes Used to Indicate Number in
Chemical Names
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NOMENCLATURE (cont)

• Binary Covalent Compound Type III (Table 2.2)
• Compounds formed from two nonmetals in which
  electrons are shared in chemical bond.
• Name more cation-like first, then the more
  anion-like) second with ide ending. Hydrogen
  is almost always named first.
• Indicate number of each using prefix as needed.
  (T2.6)
• Note historic names (water, ammonia)

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Table 2.6 Prefixes Used to Indicate Number in
Chemical Names