Atoms, Molecules, and Ions

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Chapter 2

• Atoms, Molecules, and Ions

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Matter

• What accounts for matters secrets?
• Atomists Democritus
• All things are made of Fire Herclitus
• Four Elements Aristotle

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Conservation of Mass and Law of Definite
Proportions

• Robert Boyle (16271691) Provided evidence for
  the atomic nature of matter.
• Element - A substance that cannot be chemically
  broken down further
• Joseph Priestley (17331804)

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Conservation of Mass and Law of Definite
Proportions

• Antoine Lavoisier (1743-1794)

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Conservation of Mass

• Law of Mass Conservation Mass is neither created
  nor destroyed in chemical reactions.
• Hg(NO3)2 2 KI ? HgI2 2KNO3
• 3.25g 3.32g ? 4.55g
  2.02g
• 6.57g
  6.57g

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Law of Definite Proportions

• Law of Definite Proportions In a unique compound
  the elements will always be found in the exact
  same ratio.

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Daltons Atomic Theory and the Law of Multiple
Proportions

• John Dalton (17661844) Proposed explanations
  for the laws of mass conservation and definite
  proportions.
• Postulate 1 Elements are made of atoms
• Postulate 2 Atoms of the same element have the
  same properties (including mass). Atoms of
  different atoms have different properties
• Postulate 3 Compound are comprise of elements
  joined together in small whole ratios
• Postulate 4 Chemical reactions only rearrange
  the way the atoms are combined

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Daltons Atomic Theory and the Law of Multiple
Proportions

• Law of Multiple Proportions
• When two elements form two different compounds,
  the mass ratios are related by small whole
  numbers.

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The Structure of Atoms Electrons

• Elements are composed of atoms
• Compounds are composed of atoms of elements in a
  given ratio
• What does an atom look like?

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The Structure of Atoms

• Structure of the Atom

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The Structure of Atoms

• Comparison of Subatomic particles

Particle Grams amu Coulombs e
Electron 9.109382 x 10-28 0.0005485799 -1.602176 x 10-19 -1
Proton 1.672622 x 10-24 1.007276 1.602176 x 10-19 1
Neutron 1.674927 x 10-24 1.008665 0 0
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Atomic Number

• protons in an atom determines the element
• atomic number (Z) - Atomic number is found on the
  periodic table
• electrons protons in a neutral atom

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Mass Number

• mass of the atom neutrons protons
• Mass number protons neutrons
• An element may have more than one mass
• Hydrogen, Deuterium, Tritium
• Isotopes Atoms with identical atomic numbers,
  but different mass numbers.
• Due to different of neutrons NOT protons

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Atomic Mass

• Atomic Mass A weighted average of the isotopic
  masses of an elements naturally occurring
  isotopes.
• Unit atomic mass unit (amu)

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Example

• Chlorine has two naturally occurring isotopes
  with an abundance of 75.77 and an isotopic mass
  of 34.969 amu, and with an abundance of 24.23
  and an isotopic mass of 36.966 amu. What is the
  atomic mass of chlorine?

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Compounds and Mixtures
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Chemical Bonds

• 2-types of bonding are found in compounds
• Ionic bond
• Covalent bond

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Ionic Bond
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Molecules, Ions and Chemical Bonds

• Ionic Bonding (Ionic Solids) Occur between metal
  and non-metal

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Ionic Bonds
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Problem

• Which of the following ions occurs commonly? 
• A.  N3
• B.  S6
• C.  O2-
• D.  Ca
• E.  Cl

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Ionic Bonds
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Ionic Bonds

• Formula for Ionic Compounds Ions combine to
  form neutral compounds

Examples Na and Cl combine to form NaCl. Ca2
and Cl combine to form CaCl2. Al3 and Cl
combine to form AlCl3. Fe2 and Cl- combine to
form FeCl2.
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Molecules, Ions, and Chemical Bonds
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Naming Chemical Compounds

• Naming Ionic Compounds - name the cation, then
  name the anion.
• The positive ion (the metal or ammonium)
• Single charge or ammonium write its name
• More than one possible charge
• Write the elements name
• Indicate the magnitude of charge as a roman
  numeral in parenthesis
• The negative ion (non-metal or polyatomic ion)
• Non-metal element - write root of element name
  with suffix ide
• Polyatomic write the ions name

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Problem

• Which one of the following combinations of names
  and formulas of ions is incorrect? 
• A.  O2- oxide
• B.  Al3 aluminum
• C.  NO3- nitrate
• D.  PO43- phosphate
• E.  CrO42- chromate

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Problem

• Which one of the following combinations of names
  and formulas of ions is incorrect? 
• A.  Ba2 barium
• B.  S2- sulfate
• C.  CN- cyanide
• D.  ClO4- perchlorate
• E.  HCO3- bicarbonate

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Problem

• Convert the names into formulas and the formulas
  into names
• Sodium oxide
• BaO
• CoCl2
• (NH4)2S
• Zinc Acetate
• Chromium (VI) oxide

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Covalent Bond
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Molecules, Ions and Chemical Bonds

• Covalent Bonding (Molecules) Between 2
  non-metals or a non-metal and a metalloid.

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Covalent Bonds
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Naming Chemical Compounds

• Naming Binary Molecular Compounds
• Identify which element is more cationlike.

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Naming Chemical Compounds

• If cation-like element is H and anion-like
  element is O, S, Se, or a halogen
• Name hydrogen
• Name the anion-like element using root and ide
  ending

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Naming Chemical Compounds

• All other non-metal / metalloid combinations
• Name the cation-like element
• Name the anion-like element with root and ide
• Using prefixes indicate how many of each atom is
  present

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Covalent Compounds

• Formula
• Translate name of each element
• Make the prefix of the element its subscript

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Problem

• Convert formulas into names and names into
  formulas
• PCl3
• Diiodine pentoxide

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Naming Compounds

• Acids are a special type of covalent compound
• Acids are species that dissociate to form H
  cations and an anion when added to water.
• Hence you will need to be told that they are
  aqueous compounds (aq)
• Acids are typically indicated by writing the H
  first in the formula
• Elemental symbols are typically written in
  alphabetical order

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Naming Compounds

• Acids cont.
• For current purposes, acids are going to be
  described as aqueous compounds of H combined with
  a group 17 element or a polyatomic ion.
• H with group 17 elements or cyanide
• Named as hydro 17 element root ic
• H with all other polyatomic ions
• Root of polyatomic ions ending in -ate ic
• Root of polyatomic ions ending in ite ous

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Problem

• What is the name of the acid formed when HBr gas
  is dissolved in water? 
• A.  bromic acid
• B.  bromous acid
• C.  hydrobromic acid
• D.  hydrobromous acid
• E.  hydrobromidic acid

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Optional Homework

• Text 2.26, 2.28, 2.29, 2.38, 2.46, 2.48, 2.50,
  2.52, 2.54, 2.56, 2.58, 2.68, 2.78, 2.82, 2.84,
  2.86, 2.88, 2.90, 2.96, 2.100, 2.104, 2.112
• Chapter 2 Homework from website