2 Atoms, Molecules, and Ions
※ From alchemy to chemistry
17th century – modern science began to emerge
Up rise of mechanical philosophy
Francis Bacon (1561–1626)
Experiments should be planned
Results should be repeated and verified
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※ Fundamental chemical laws
Lavoisier –
Law of conservation of mass
(quantitative analysis)
1789 published Traité élementaire de Chimie
Element: substances that had not yet been decomposed
Proust (1754–1826)
Law of constant composition
(定組成定律；by 1808 generally accepted)
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Dalton (1766–1844)
Law of definite proportion
(theoretical basis):
Compound is composed of atoms
with the same combination
(定比定律)
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Ex.
Two ways to combine C & O
Compound I
Compound II
1gC
1gC
1.33 g O
2.66 g O
Law of multiple proportions (倍比定律)
(Berzelius, 1779–1848, analyzed
2000 inorganic compounds in 10
years)
Problem
Could not determine absolute formula
CO
C2O2 ---------
CO2
C2O4 ---------
※ Dalton’s atomic theory (1803~8)
1.
2.
3.
4.
Element – composed of atoms
Different element – different atoms
Compound – atoms combined in a definite ratio
Chemical reaction – reorganize atoms
Atomic weights (1805)
1 g H, 8 g O  water
If AW(O) = 8 × AW(H)
 water = OH  Principle of
simplicity
If AW(O) = 16 × AW(H)  water = OH2
etc.
(by 1826, Berzelius’s table contained 49 elements)
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1809 Joseph Louis Gay-Lussac (1778–1850)
Studied reactions of gases
existence of simple whole number
Ex.
2 H2 + 1 O2  2 H2O
1 H2 + 1 Cl2  2 HCl
1 N2 + 1 O2  2 NO
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1811 Amadeo Avogadro (1776–1856)
Avogadro hypothesis
Same T, P
equal volumes of different gases
contain the same number of particles
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Proposed
diatomic molecules (accepted in 1860)
Water = H2O
Problem: the idea of diatomic molecule was not accepted
※ Another new era
(Cannizarro’s interpretation)
1860 First International Chemical Congress at Karlsruhe
Organizer: Kekule (1829–1896) and Welzein (1813–1870)
Cannizarro (1826 – 1910)
1. Compounds contain whole number of atoms
2. Adopt Avogadro’s hypothesis
AW(H) = 1  MW(H2) = 2
W1L O2
W1L H2

16 32

1
2
AW(O) = 16
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3
Carbon dioxide: relative mass = 44
(compared with hydrogen)
with 27% of C (44 × 0.27 = 12)
44 g CO2:
12 g C
If AW(C) = 12
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

32 g O
CO2
CO
How can we determine the AW of C?
Methane
Rel. mass
16
%C
75
Rel. mass
12
Ethane
Propane
Butane
30
44
58
80
82
83
24
36
48
CO2
44
27
12
16 × 0.75
Conclusion: AW(C) = 12
※ Periodic table
1869
Mendeleev The 1st periodic table
1A
H 2A
Li Be
NaMg
K Ca Sc Ti
Rb Sr Y Zr
Cs Ba La Hf
Fr Ra Ac Rf
8A
3A 4A 5A 6A 7A He
B C N O F Ne
Al Si P S Cl Ar
V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
NbMo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Ta W Re Os Ir Pt AuHg Tl Pb Bi Po At Rn
Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
A relationship between AW and properties
Eight statements were made
1. Periodicity of properties
2. Some elements with similar properties have similar AW
(Pt, Ir, Os), or increase regularly (K, Rb, Cs)
3. The order of AW corresponds with element’s valencies
4. Most widely distributed elements in nature have small AW
5. AW determines the character of an element
6. New elements may be expected
Ex. AW of 65 similar to Al(27.4)
AW of 75 similar to Si(28)
 Ga(69.7) in 1875
 Ge(73) in 1886
7. Some AWs may need correction
Ex. Te(128) should be 123~126
 127.6
8. The table reveals new analogies between elements
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※ Characterization of atom
1856–1940 J. J. Thomson
Study of cathode ray tubes
 cathode ray
 different metals, same result
Thomson’s experiments
negatively charged particles
(electrons)
e
 1.76  10 8 C/g
m
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1906 in physics
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Thomson’s plum pudding model (1904)
positively charged plasma
negatively charged
1909 Robert A. Millikan (1868–1953)
determined the charge of electron
 the mass of e = 9.11 × 1031 kg
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1923 in physics
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※ Nuclear atom
Early 20th century: radioactivity
1898 a particle: +2 charge
mass = 7300 Me
1906 Rutherford
Metal foil
a particle
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1908 in chemistry
Most of the particles passed through
but some particles were deflected at large angles
1911 Rutherford’s model
e
e
e
Modern views
Electrons
Protons
Neutrons
Tiny heavy nucleus
with positive charge
Representation:
mass number
atomic number
23
11Na
Isotopes: same # of protons but
different # of neutrons
Molecules:
Ions:
Atoms combined through chemical bonds
Cations (ex. Na+)
Anions (ex. Cl)
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※ Naming simple compounds
(nomenclature)
1782 De Morveau
A substance should have one fixed name,
which should reflect its composition if known,
… chosen from Greek or Latin roots
1787 Lavoisier
“Methods of Chemical Nomenclature”
統一命名法則： IUPAC systematic nomenclature
國際純化學暨應用化學聯合會
International Union of Pure and
Applied Chemistry
◎ Type I：binary ionic compounds 離子化合物
M+ A
metal cation 金屬陽離子(only one charge type)
A ： anion 陰離子
M+ ：
Rules：
1. Cation first
2. Cation takes the name of the atom
Ex.
NaCl sodium chloride
3. Anion with -ide suffix
Ex.
chlorine  chloride
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Some common cations and anions
H+
Li+
Na+
K+
Mg2+
Ca2+
Ba2+
Al3+
Li3N
NaN3
MgO
hydrogen
lithium
sodium
potassium
magnesium
calcium
barium
aluminum
H
OH
F
Cl
Br
I
O2
S2
N3
N3
lithium nitride
sodium azide
magnesium oxide
hydride
hydroxide
fluoride
chloride
bromide
iodide
oxide
sulfide
nitride
azide
(氮：nitrogen)
(氧：oxygen)
◎ Type II：binary ionic compounds
cation with more than one type of charge
Ex.
Fe(II)Cl2, Fe(III)Cl3
FeCl2 IUPAC: iron(II) chloride
Common: ferrous chloride
FeCl3 IUPAC: iron(III) chloride Common: ferric chloride
Common names: -ous (lower charge), -ic (higher charge)
△ Some common type I cations
IA, IIA cations
IIIA: Al3+ (aluminum)
Transition metals:
Zn2+, Ag+
(Zn: zinc; Ag: silver)
1A
H 2A
Li Be
Na Mg
K Ca Sc Ti
Rb Sr Y Zr
Cs Ba La Hf
Fr Ra Ac Rf
8A
3A 4A 5A 6A 7A He
B C N O F Ne
Al Si P S Cl Ar
V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
NbMo Tc Ru Rh Pd AgCd In Sn Sb Te I Xe
Ta W Re Os Ir Pt AuHg Tl Pb Bi Po At Rn
Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
lanthanides: Ce Pr NdPmSmEu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np PuAmCmBk Cf Es FmMd No Lr
actinides:
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△ Some common type II cations
Cu+： cuprous
Sn2+： stannous
Hg22+： mercurous
Cu2+： cupric
Sn4+： stannic
Hg2+： mercuric
Al2O3 aluminum oxide (alumina；礬土)
Ex.
only one type of charge
CoBr2 cobalt(II) bromide
△ Polyatomic anions
SO42： sulfate (硫酸根)
SO32： sulfite (亞硫酸根)
Rules: -ate (with more O)，-ite (with fewer O)

ClO ： hypochlorite (次氯酸根)
ClO2：chlorite (亞氯酸根)
ClO3：chlorate (氯酸根)
ClO4：perchlorate (過氯酸根)
Rules：hypo (with fewer O)，per (with more O)
NO3： nitrate (硝酸根)
NO2： nitrite (亞硝酸根)
PO43： phosphate (磷酸根)
HPO42： hydrogen phosphate
H2PO4： dihydrogen phosphate
CO32： carbonate (碳酸根)
HCO3： hydrogen carbonate (also called bicarbonate)
O22：
peroxide (過氧根)
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△ Polyatomic cation
NH4+ ammonium ion
Ex. NH4Cl ammonium chloride
△ Prefix (to indicate number)
monoditritetrapentahexaheptaocta-
1
2
3
4
5
6
7
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◎ Type III：binary covalent compounds
contain two nonmetals
Very similar to ionic compounds
N2O dinitrogen monoxide (common: nitrous oxide)
NO nitrogen monoxide (or oxide) (common: nitric oxide)
NO2 nitrogen dioxide
N2O3 dinitrogen trioxide
N2O4 dinitrogen tetraoxide
N2O5 dinitrogen pentaoxide
Note:
monooxide but not monoxide (N2O and NO are exceptions)
pentaoxide but not pentoxide
mono never used for the first element
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◎ Acids (酸)
△ Without oxygen
HCl hydrochloric acid
H2S hydrosulfuric acid
HCN hydrocyanic acid
△ With oxygen
SO42： sulfate
SO32： sulfite
(hydrogen chloride)
(hydrogen sulfide)
(hydrogen cyanide)
H2SO4： sulfuric acid
H2SO3： sulfurous acid
HNO3 : nitric acid
HNO2 : nitrous acid
HClO： hypochlorous acid (次氯酸)
HClO2：chlorous acid (亞氯酸)
HClO3：chloric acid (氯酸)
HClO4：perchloric acid (過氯酸)
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