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CHAPTER 2
ATOMS and MOLECULES
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Periodic Table
• Atomic Mass –number below the element–not whole numbers because
the masses are averages of the masses of the different isotopes of the elements
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Ions
• Are charged species
• Result when elements gain electrons or lose electrons
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2 Types of Ions
• Anions – (-) charged•Example: F-
• Cations – (+) charged•Example: Na+
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Highly Important!
• Gain of electrons makes element (-) = anion
• Loss of electrons makes element (+) = cation
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Charges• When elements combine, they have to be
in the form of IONS.• Cations and anions combine to form
compounds.• For a neutral compound, the sum of the
charges must be ZERO.• For a polyatomic ion, the sum of the
charges must equal the charge of the ION.
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Isotopes
• Are atoms of a given element that differ in the number of neutrons and consequently in atomic mass.
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Example
Isotopes % Abundance12C 98.89 %13C 1.11 %14C 11C
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–For example, the mass of C = 12.01 a.m.u is the average of the masses of 12C, 13C and 14C.
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Determination of Aver. Mass
• Ave. Mass = [(% Abund./100) (atomic mass)] + [(% Abund./100) (atomic mass)]
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Take Note:• If there are more than 2
isotopes, then formula has to be re-adjusted
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Sample Problem 1
• Assume that element Uus is synthesized and that it has the following stable isotopes:–284Uus (283.4 a.m.u.) 34.6 %–285Uus (284.7 a.m.u.) 21.2 %–288Uus (287.8 a.m.u.) 44.20 %
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Solution
• Ave. Mass of Uus =• [284Uus] (283.4 a.m.u.)(0.346)• [285Uus] +(284.7 a.m.u.)(0.212)• [288Uus] +(287.8 a.m.u.)(0.4420)• = 97.92 + 60.36 + 127.21 • = 285.49 a.m.u (FINAL ANS.)
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Oxidation Numbers
• Is the charge of the ions (elements in their ion form)
• Is a form of electron accounting
• Compounds have total charge of zero (positive charge equals negative charge)
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Oxidation States
• Are the partial charges of the ions. Some ions have more than one oxidation states.
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Oxidation States
• - generally depend upon the how the element follows the octet rule• Octet Rule – rule allowing
elements to follow the noble gas configuration
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Nomenclature
• - naming of compounds
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Periodic Table
• Rows (Left to Right) - periods
• Columns (top to bottom) - groups
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Rule 1 – IONIC COMPOUNDS
• Metals w/ Fixed Oxidation States–Name metal or first element as is- Anion always ends in “–ide”
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Terminal element or anion
• O - oxide P - phosphide• N - nitride Se - selenide• S - sulfide Cl - chloride• F - fluoride I - iodide• Br - bromideC - carbide
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Note
• Only elements that come directly from the periodic table WILL end in –IDE.
• POLYATOMIC IONS will be named AS IS.
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Name the following:
• CaO -• NaCl -•MgO - • CaS- • Na3N -
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Answers:
• CaO - calcium oxide• NaCl - sodium chloride•MgO - magnesium oxide• CaS- calcium sulfide• Na3N - sodium nitride
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Where do the subscripts come from?
• Answer: From the oxidation states of the ions.
• Remember: Ions are the species that combine.
• Target: Compounds! (No charges!)
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Second Rule
• II. Ionic Compounds - Metals with no fixed oxidation states (Transition Metals) except for Ag, Zn and Al
• Metal(Roman #) + 1st syllable + ide
–Use Roman numerals after the metal to indicate oxidation state
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Name the following:
• Copper (I) sulfide• Iron (II) oxide• Tin (II) iodide• Iron (III) nitride
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Answers:
• Copper (I) sulfide Cu2S• Iron (II) oxide FeO• Tin (II) iodide SnI2
• Iron (III) nitride FeN
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What about…….?
• Cesium hydroxide• Iron (III) acetate• Lithium phosphate• Aluminum Sulfite• Lead (II) sulfate• Silver nitrate
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POLYATOMIC IONS
• Consist of more than 1 element.
• Have charges.
• Ex. SO4 2-, SO3 2-, PO4 3-,PO3 3-
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Rule 3 – Covalent Compounds• III. For Non-metals (grps IV, V, VI VII), use
prefixes.Mono – 1 Hepta - 7Di - 2 Octa - 8Tri – 3 Nona - 9Tetra – 4 Deca - 10Penta – 5Hexa - 6
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Rule 3 – Covalent Compounds (only have Non- Metals)
• Name 1st element as is. Use prefix, if necessary.
• Prefix + 1st element + prefix + 1st syllable of anion + ide
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Name the following compounds
• CO2 - carbon dioxide
• N2O – dinitrogen oxide
• SO3 – sulfur trioxide
• N2O5 – dinitrogen pentoxide
• P2S5 – diphosphorus pentasulfide• CO – carbon monoxide
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Naming Acids
• I. Acids without Oxygen–Use hydro + 1st syllable + “- ic acid”
• Example: HCl = hydrochloric acidHCN = hydrocyanic acid HBr = hydrobromic acid
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II. Acids with oxygen• Polyatomic “ate” converts to “ic” + acid• Polyatomic “ite” converts to “ous” + acid
- H2SO3 sulfurous acid
–H2SO4 sulfuric acid
–HNO3 nitric acid
–HNO2 nitrous acid
–H3PO4 phosphoric acid
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Trick!
• If anion ends in “ – ate”, acid ends in “ – ic”
• Example:• HClO4 perchlorate perchloric acid
• HClO3 chlorate chloric acid
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Trick!
• If anion ends in “ – ite”, acid ends in “ – ous”
• Example:• HClO2 chlorite chlorous acid
• HClO hypochlorite hypochlorous acid
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Name the following:
• HBrO4 (perbromate)
• HBrO3 (bromate)
• HBrO2 (bromite)• HBrO (hypobromite)
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Pure Acids (not diluted)
• Simply use Rule 3. Use prefixes, if necessary.