Download Atoms, Molecules, and Ions

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Chapter 2
Atoms, Molecules, and Ions
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The Atomic Theory
Proof atoms exist
Laws of Chemical Combination
Atomic Theory of Matter: Dalton (1808)
Hypotheses were derived from 3 Laws of Chemical Combination
1.
All matter is composed of tiny particles called atoms
2.
All atoms of a given element are identical, but atoms of
different elements differ in size, mass and chemical properties
F
H
Fluorine 18 amu
3.
Hydogen atom 1 amu
Compounds are formed when atoms of different elements
unite in fixed proportions.
74amu = 72amu
F
F
4.
F
F
+
2amu
+
H
H
38amu + 36amu = 74amu
F
H
F
F
+
H
F
A chemical reaction involves atomic rearrangement. No atoms
are created or destroyed
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Law of Definite Proportions
A compound will always have same chemical composition
Each product formed from definite proportions of reactants
Same mass proportions & atomic ratios of elements present
8 Water molecules
16H + 8O  8H2O
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Law of Multiple Proportions
When 2 different compounds made of the same 2 elements
are compared, the masses of one element combines with
a fixed mass of the second element. The combination is in
a ratio of small whole numbers.
Open face sandwich
1 bread + 1 filling
1:1 ratio
Regular sandwich
2 bread + 1 filling: 2/1
2:1 ratio
Compounds are formed when atoms of different elements
unite in fixed proportions
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Law of Conservation of Mass
Total mass is constant during a chemical reaction
Mass of reactants must exactly match mass of products
2lbs potatoes + 3 ounces milk+ 1 ounce butter =
2.25 lbs mashed
potatoes
Also called a mass balance
11.1g H2 (g) + 88.9g O2 (g) = 100.0g H2O (l)
No matter can be created or destroyed
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Structure of the Atom
What’s on the inside
The Electron and Cathode Rays (1890’s)
Electricity causes ray to be deflected in a vacuum
Few molecules: minimal molecular interference
Applied magnetic field or electric field deflects ray
Ray is attracted to positively charged anode, so it must be
made of negatively charged particles
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Millikan Oil Drop Experiment
Finalized related charge and mass of electron
JJ Thompson
Ratio of cathode ray particle’s charge to mass =–1.76 X 108 C/g
Negatively charged particle is called an electron
Robert Millikan
Charge on an electron
e = -1.602 X 10-19 C
Mass of an electron
me= 9.10 x 10-28g
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The Atom
J. J. Thomson’s Raisin Pudding Model
Positively charged sphere with electrons imbedded inside
Rutherford’s Experiments
Shot  particles through gold foil
Results:
Hit detector: No interference
Deflected from straight line: Charge interference
Reflected back toward emitter: Hit + small center
The Atom and Sub-Atomic Particles
Protons
large, positively charged particles in small central nucleus
Electrons
tiny, negatively charged particles in cloud around the nucleus
Neutrons
large, neutral particle in nucleus
electron
neutron
nucleus
proton
Elements are not electrically charged
Must have equal numbers of protons and electrons
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Neutrons
Atomic particle with same mass as proton
Discovered by James Chadwick
No charge- accounts for extra mass of isotopes
Change in mass, no change in chemical properties
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Atomic Number, Mass Number
and Isotopes
Differences between atoms
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Atomic Symbols
Atomic Number (Z)
# protons in a nucleus
Determines element identity
Located lower left on symbol
Mass Number (A)
# protons + # neutrons
Determines isotope identity
Located upper left on symbol
A
E
Z
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Cl
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Isotopes
Elements with the same number of protons and
electrons, but differing number of neutrons
Used in chemistry for structure identification or to follow a
particular molecule through a reaction
Example: hydrogen and deuterium
Water, H2O
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Heavy water, D2O
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H has 1 proton and 0 neutrons
Most abundant
D (deuterium) has 1 proton & 1 neutron
Occurs 1/6700 molecules
H
1
1
H
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The Periodic Table
Elemental Organization
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Mendeleev’s Periodic Table 1869
Arranged the known elements in order
of increasing atomic mass from left to right
and from top to bottom in groups.
Elements with similar properties
are placed in same column.
O
I
II
III
IV
V
VI
VII
H
1
He
Li
Be
B
C
N
O
F
4
7
9
11
12
14
16
19
Ne
Na
Mg
Al
Si
P
S
Cl
20
23
24
27
28
31
32
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Ar
K
Ca
Ge
As
Se
Br
40
39
40
75
79
80
Kr
Rb
Sr
In
Sn
Sb
Te
I
84
85
88
115
119
122
128
127
Xe
Cs
Ba
Tl
Pb
Bi
131
133
137
204
207
209
Rn
(222)
Used table to predict properties of
undiscovered elements
Eka-Silicon
MM: 72
Density: 5.5g/mL
Color: dirty gray
Germanium
MM: 72.6
Density: 5.47g/mL
Color: grayish white
The Modern Periodic Table
Green Metals
Blue
Nonmetals
Pink
Metalloids
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Ductile, malleable, conductive, positive ionic charge
Brittle solids, often gases or liquids, negative charge
Properties of both metals and nonmetals
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Predicting Ionic Charge from the Periodic Table
Alkali
Metals
1A
##
##
Main Group Elements Only
Halogens
Alkali Earth
Metals
Noble
Gases
8A
1.0
2.0
H
He
1.0
3.0
2A
4.0
3A
5.0
4A
6.0
5A
7.0
6A
8.0
7.0
9.0
4.0
10.0
Li
Be
B
C
N
O
F
Ne
6.9
9.0
10.8
12.0
14.0
16.0
19.0
20.2
Goal: Get to column 8A by going to the right or left
Right: Count each box as -1 until reaching 8A
Left: Count each box as +1 until reaching 8A in previous row
The correct charge is usually the smallest number
Left Side (metals):
Li1+ or Li-7
Mg2+ or Mg6Right Side (nonmetals):
O2-, F1-, He0, Ne0
Center (metalloids):
B3+ (B5-), C4+ C4- , N5+, N3Transition metals become cations: charge is unpredictable
Charge is designated with a Roman numeral
Iron (III) oxide contains Fe3+, Iron (II) oxide contains Fe2+
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Groups in the Periodic Table
Alkali Metals
Group 1A
+1 charge
Highly reactive
Halogens
Group 7A
-1 charge
Highly reactive
Diatomic molecules
Alkali Earth Metals
Group 2A
+2 charge
Reactive
Noble Gases
Group 8A
+ charge (if charged)
Inert
Transition metals
Center of table
Varying (+) charge
Use Roman numerals
Lanthanides & Actinides
Bottom of table
Very reactive
+ charge
Often radioactive
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Elements to Memorize
Know name and symbol
First 4 rows of periodic table
Including 1st row of transition metals
Additional elements
Ag: Silver
Pb: Lead
I:
Iodine
Hg: Mercury
Lanthanides and actinides
Know where they are in the periodic table
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Chemical Formulas
Atomic ratios in molecules
Molecular Formulas
Symbolic representation of molecular composition
Empirical: Ratio of atoms NH2 instead of N2H4
Molecular: Types & # of atoms
Structural: Relationship between atoms
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Ionic Compounds (salts)
Atoms in a reaction may gain or lose electrons
Both atoms become charged and are called ions
Anion: atom gaining the electron is negatively charged
Cation: atom losing the electron is positively charged
Will bind together to form crystals
The net charge on the compound is 0
Cations & anions balance out
Get charges from periodic table
No distinct molecular units
Positive charge of cation attracts all nearby anions
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Polyatomic Ions
Lose or gain electrons as a group
Charge is spread over 2 or more atoms
Memorize the following polyatomic ions!
Ammonium
Phosphate
Hydroxide
Cyanide
Permanganate
Carbonate
NH4+
PO43OHCNMnO4CO32-
Hydronium H3O+
Acetate
CH3COONitrate
NO3Sulfate
SO42Chlorate ClO3Perchlorate ClO4-
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Formula of Ionic Compounds
Must match charges!
2 x +3 = +6
3 x -2 = -6
Al2O3
Al3+
1 x +2 = +2
2 x -1 = -2
Ca2+
CaBr2
1 x +2 = +2
Br1 x -2 = -2
Na2CO3
Na+
O2-
CO32-
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Naming Compounds
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Molecular Names
Names and formulas have 2 parts, 1 for each element:
Dinitrogen Tetroxide
N2O4
1st word is for 1st element
N: Nitrogen
2nd word is stem of element name
change ending to “–ide”
O: Oxygen
O: Oxide
Subscripts designate # of atoms,
Prefixes used to name atoms:
Memorize prefixes
# atoms
1
2
3
4
5
prefix
mono
di
tri
tetra
penta
# atoms
6
7
8
9
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N2: Dinitrogen
O4: Tetroxide
prefix
hexa
hepta
octa
nona
deca
Names of Ions and Ionic Compounds
For cations: add the word ION after element name
For anions: change the element name ending to –ide first
Sodium Chloride: NaCl
Na
loses 1 eNa+
Sodium ion
Cl
gains 1 eNet Charge: (+1) + (-1) = 0
ClChemical Formula is NaCl
Chloride ion
Aluminum Oxide: Al2O3
Al (+3 charge)
loses 3 eAl3+
Aluminum ion
O (-2 charge)
gains 2 eNet Charge: 2(+3) + 3(-2) = 0
O2Chemical Formula is Al2O3
Oxide ion
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Acid
Acids and Bases
Arrhenius: Compound ionizes in H2O to form H+ & anions
Name by changing anion –ide ending to –ic acid
Add hydro to acids with HX formula: Hydrocchloric acid HCl
Bronsted acids: H+ grabs H2O to form H3O+ in water
Base
Arrhenius: Compound ionizes in H2O to form OH- & cations
Name as salts: All hydroxide salts are considered bases
Bronsted base: Pulls H+ from H2O so NH3 is a base:
H2O + NH3  OH- + NH4+  NH4OH
Neutralization
Reaction between acid & base
H+ + OH- H2O and cation + anion  salt
HCl + NaOH H2O + NaCl (aq)
Common acids and bases
Memorize
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Acids
Hydrochloric Acid:
Sulfuric Acid:
Chloric Acid:
Perchloric acid:
HCl
H2SO4
HClO3
HClO4
Carbonic Acid:
Nitric Acid:
Phosphoric Acid:
Acetic Acid:
H2CO3
HNO3
H3PO4
CH3COOH
Bases
Sodium hydroxide: NaOH
Ammonium hydroxide: NH4OH
Lithium hydroxide: LiOH
Potassium hydroxide: KOH
(actually ammonia, NH3 in H2O)
Hydrates
Compound is associated with a fixed number of
water molecules
Naming Hydrates
Copper(II)sulfate
CuSO4
Use numerical prefixes for
# of water molecules
Then add the word “hydrate”
A dot shows H2O association
Water molecules part of mass
Copper(II)sulfate pentahydrate
CuSO45H2O
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Naming Oxoacids and their Anions:
Reference Only
HClO4
Perchloric acid
HClO3
Chloric acid
HClO2
Chlorous acid
HClO
Hypochlorous acid
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