chapter two: atoms, molecules & ions atomic theory & structure isotopes, numbers &...
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Chapter Two:
Atoms, Molecules & Ions
Atomic Theory & Structure
Isotopes, Numbers & Masses
Periodic Table
Molecules, Ions, Compounds & Formulas
Naming Species
Atomic Theory and StructureWhat is the smallest piece of matter possible?
Democritus called the smallest particles “atomos”
Dalton’s atomic theory of matter: elements are composed of small particles -- atoms all atoms of an element are identical atoms are not created or destroyed chemically compounds formed by chemical combination of two or more elements a given compound has same relative number & type of atoms (law of constant composition) atoms retain character during chemical rxns. only undergo rearrangement (conservation of matter)
Law of Multiple ProportionsIf two elements, A & B, form more than one
compound, the masses of B that can combine with a given mass of A are in a ratio of small whole numbers
C
C O
O O12 g of Carbon & 32 g of Oxygen
12 g of Carbon & 16 g of Oxygen
2 x
carbon dioxide
carbon monoxide
Subatomic Particles-J.J. Thompson determined charge:mass ratio of e-, 1897-Robert Millikan measured charge of e-, 1909-Thompson developed “plum pudding” model of atom-Rutherford developed “nuclear” model of atom
alpha particle source
detector
Modern Atomic Structure
PARTICLE CHARGE* MASS (AMU)
Proton +1 1.0073
Neutron 0 1.0087
Electron -1 5.486 x 10-4
* unit charge = 1.602 x 10-19 C (coulomb)
amu (u) -- atomic mass unit = 1.66054 x 10-24 g
Atomic Numbernumber of protons in an atomdefines an elementshown as the symbol subscript 6C
Mass Numbertotal number of protons plus neutronswill vary between isotopesshown as the symbol superscript12C
Isotopeselements which have the same atomic number but different mass numbers12C6 13C6 14C6 are isotopes
Periodic Table–Allows for organization of elements
–Allows for grouping of elements in terms of physical and chemical characteristics
Metals, Non-metals & Metalloids
–Group 1A Alkali Metals
–Group 2A Alkaline Earth Metals
–Group 6A Chalcogens
–Group 7A Halogens
–Group 8A Nobel Gases
–B Groups Transition MetalsKnow these !!
Molecules and Molecular Compounds
•Molecule — the smallest particle of a compound that can be identified as that compound
— chemical combination of two or more atoms
— a pure substance
• Chemical Formula— a symbol representation of a molecule/compound— shows the type and ratio of atoms in a molecule
type is given by symbolratio is given by a subscript to right of symbol
Examples:
H2O
H2O2
CO2
CO
O2
Molecule Ratio
2 : 1
2 : 2
1 : 2
1 : 1
-
heteroatomic
heteroatomic
heteroatomic
heteroatomic
homoatomic
• Formulas
—Molecular Formulas Give the type and exact number of each type
of atom
—Empirical Formulas Give only the type and simplist ratio of
atoms
H2O
H2O2
C6H6
C2H6
Molecular Formula Empirical Formula H2O
HO
CH
CH3
— Structural Formulas Show which atoms are attached to which
atoms
C2H6O
H C O C H
H
H H
H
H C C O H
H
H
H
H
dimethylether
ethanol
Ions & Ionic Compounds
• Some elements will either lose or gain one or more electrons to become charged species
• Metals– typically lose electrons, become +, cations
• Non-Metals– typically gain electrons, become -, anions
Monatomic Ions– made from a single element
• Na Na+ + 1e-
• Cl + 1e- Cl-
Na Na+1e- +
Cl Cl- + 1e-
11 p+ 11 e-
11 p+ 10 e-
17 p+ 18 e-
17 p+ 17 e-
Hints to Determine Ion Charges
• Hydrogen +1
• Oxygen - 2
• Group IA +1
• Group IIA +2
• Group VIA - 2
• Group VIIA - 1
Polyatomic Ions -- “molecules” which have a net positive or negative charge
– CO32- carbonate ion
– NH4+ ammonium ion
– OH- hydroxide ion
Prediction of Charges -- all species tend toward the most stable state
– Nobel gases are very stable– Elements add or lose electrons to “mimic” nobel gases
Ionic Compounds
• Oppositely charged ions form ionic compounds
– held together by ionic bonds due to the
electrostatic attraction between the
opposite charges
• Ionic compounds are always neutral species
• Mg2+ and Cl- form MgCl2 not MgCl
or Mg2Cl
Naming Inorganic Compounds
• Names of Monatomic Ions
– cations are named for the elements Na+ is sodium ion Al+3 is aluminum
ion Fe+2 is iron(II) ion Fe+3 is iron(III) ion (ferrous ion) (ferric ion) Cu+ is copper(I) ion Cu2+ is copper(II)
ion (cuprous ion) (cupric ion)
– anions are named for the root name of the element with the ending -ide
O-2 is oxide ion Cl- is chloride ion H- is hydride ion N-3 nitride ion
•Naming Polyatomic Ions
• Know the names, charges and formulas of the important polyatomic ions
– NH4+ ammonium ion
– CO3-2carbonate ion
– SO4-2 sulfate ion– OH- hydroxide ion
– NO3- nitrate ion
• Polyatomic ions are treated as separate entities or units
• Naming and formula rules are the same as for compounds with monatomic ions
Naming Binary Ionic Compounds
• Cations always named first• Anions always named last
– NaCl sodium chloride
– BaCl2 barium chloride
• for cations which have more than one possible charge, the charge of the ion must be given in the name– Fe2O3 iron(III) oxide– FeO iron(II) oxide
• Combinations must be neutral!
• Examples:
– 2 Na+ and 1 CO3-2 is sodium carbonate
Na2CO3
– 2 NH4+ and 1 S-2 is ammonium sulfide
(NH4)2S– 1 Ba+2 and 2 OH- is barium hydroxide
Ba(OH)2
– 3 Mg+2 and 2 PO4-3 is magnesium
phosphate Mg3(PO4)2
– 1 Na+ , 1 H+ and 1 CO3-2 is sodium hydrogen
carbonate or sodium bicarbonate, NaHCO3
Acids
• A compound that produces hydrogen ions (H+) when dissolved in water
• tastes sour• turns litmus red• has a pH less than 7• typically the formula begins with one or
more H’s– HCl(aq) hydrochloric acid
– H2SO4(aq) sulfuric acid
– HC2H3O2(aq) acetic acid
Binary Acids
• Acids which contain H and another non-metallic element
• Naming -- to the root name of the non-metallic element:– add the prefix hydro-– add suffix -ic acid
• HF(aq) hydrofluoric acid
• HBr(aq) hydrobromic acid
• HCl(aq) hydrochloric acid
Note!
Oxyacids
• Acids which contain H and O and another element (or H and a polyatomic anion containing O)
• Naming -- to the polyatomic ion name– if the suffix is -ate, change it to -ic
– if the suffix is -ite, change it to -ous
– add acid to the end of the name• HNO3 nitric acid HNO2 nitrous acid
• H2SO4 sufuric acid H2SO3 sulfurous acid
• You must know polyatomic ion names/charges
Binary Molecular Compounds
• Chemical combinations of non-metals and non-metals (no ions involved)
• The more metallic element is named first• The second element (less metallic) is named
with the ending -ide• Because there are no ions to use to
determine relative ratio of atoms we must indicate the number of each atom by a prefix– N2O3 dinitrogen trioxide– SO3 sulfur trioxide
Name the Following:
• CaI2
• Cu2O
• CuO
• Cl2O7
• HClO3
calcium iodide
copper(I) oxide
copper(II) oxide
dichlorine heptaoxide
notechloric acid
Write Formulas for the Following:• calcium hypochlorite
• Mg+2 and ClO2-
• carbon tetrachloride
• NH4+ and SO4
-2
Ca(ClO)2
Mg(ClO2)2
CCl4
(NH4)2SO4