Atoms, Molecules, and Ions
• Classification and Compositions of Matter
• Atomic Structures
– Ancient Philosophy
– Dalton’s Atomic Theory
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Isotopes
Periodic Table
Molecules and Ions
Types of Compounds
Naming Compounds
Classification of Matter
Matter According to Ancient Philosophy
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Matter is composed of four basic elements:
Earth, water, wind, and fire
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Two schools of thought emerged during
Greek Civilization:
1. Aristotle and his followers believed that matter to
be infinite – not composed of discrete unit.
2. Democritus and Leucippus believed that matter
is made of discrete units called “atomos” that is
indivisible.
The “Development” of Theory
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Many early 18th Century chemists the
combustion process;
They “observed” that when a piece of wood
burn, the mass of the ash formed is apparently
less than that of the original wood.
So, what happen to the rest of the mass of the wood?
The Phlogiston Theory
• This is their theory to explain combustion:
1.Materials burn because they contains a substance
called phlogiston;
2.During combustion the phlogiston is lost;
3.Thus, the mass of ash is less than the wood.
Really? What did they forget to do before coming to
that conclusion?
Experimental Science versus Philosophy
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Antoine Lavoisier (1743-1794) performed
quantitative experiments to study combustion
processes. The results showed that in all combustion
reactions the masses of products to be greater than
those of the material being burned.
He concluded that:
1. The Phlogiston theory was incorrect;
2. Combustion involves oxygen gas – the gain in mass
during combustion is due combination with oxygen;
3. Mass is conserved during chemical reactions.
Experimental Science versus Philosophy
• Joseph Proust (1754-1826) performed
numerous experiments to analyze the
compositions of compounds, and found that:
a given compound has a constant composition (in
mass %) regardless of its origin or sample size.
The Law of Constant Composition
Examples:
(a) Copper carbonate is always composed (by mass
%) of 51.4% Cu, 9.7% C, and 38.9% O .
(b) Sodium chloride is always composed of 39.34%
Na and 60.66% Cl, by mass.
Two Fundamental Laws of Matter
• The Law of Conservation of Mass:
During chemical reactions, the total mass of
substances is conserved. (Mass is neither created
or destroyed during chemical reaction.)
• The Law of Definite Proportions:
A given compound always contains the same types
of elements chemically combined in a fixed
proportion by mass, regardless of its origin.
Dalton’s Atomic Theory (1805)
1. Elements are made up of discrete, indivisible
particles, called atoms;
2. Atoms of the same element are identical, but are
different for different elements;
3. A compounds is formed when atoms of different
elements combined in simple whole number ratios;
4. The smallest unit of a given compound always
contains the same number and type of atoms;
5. Atoms are not created or destroyed during chemical
reactions.
Principle of Chemical Combination
• Law of Multiple Proportion:
When two elements react to form more than one type of
compounds, there exist a simple ratio of the masses of
one of the elements that combine with a fixed mass of
the other element in these compounds;
Example: Carbon reacts with oxygen to form two compounds,
X and Y. In X, 1.00 g of carbon combines with 1.33 g of
oxygen, and in Y, 1.00 g of carbon combines with 2.66 g of
oxygen. The mass ratio of oxygen in compounds X and Y is
1:2. If X = CO, then Y = CO2
Exercise #1: Law of Multiple Proportions
• Sulfur reacts with fluorine to form three different
compounds, A, B and C. In compound-A, 1.000 g of
sulfur combines with 1.185 g of fluorine; in
compound-B, 2.370 g of fluorine was found for every
gram of sulfur, and in compound-C, the mass ratio of
fluorine to sulfur is 3.556-to-1. Show that these data
conform with the law of multiple proportions. Derive
the formula of compounds A, B, and C.
Gay-Lussac Interpretation of Combining Volume
Principle of Chemical Combination
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Gay-Lussac’s Law of Combining Volumes:
In reactions that involve gaseous reactants and
products, there exist “simple ratios” of their volumes
measured under the same temperature and pressure.
Examples:
1. 1 volume of hydrogen reacts with 1 volume of
chlorine to form 2 volumes of hydrogen chloride;
2. 2 volumes of hydrogen reacts with 1 volume of
oxygen to form 2 volumes of water vapor.
Interpretation of Gay-Lussac’s Experiments
• According to Avogadro’s law: “under same
temperature and pressure, equal volumes of gases
contain the same number of molecules”
• 1 L of hydrogen + 1 L of chlorine  2 L of hydrogen chloride
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This implies:
1 H-molecule + 1 Cl-molecule  2 HCl molecules.
Hydrogen and chlorine molecules must be diatomic (2
atoms per molecule), and the reaction may be written as
follows:
H2(g) + Cl2(g)  2 HCl(g)
Interpretation of Gay-Lussac’s Experiments
• 2 L of hydrogen + 1 L of oxygen  2 L of water
vapor implies:
2 H-molecules + 1 O-molecule  2 water
molecules.
a) Hydrogen and oxygen gases contains diatomic molecules
(H2 and O2), and water has the formula H2O.
b) The above reaction can be represented by the equation:
2H2(g) + O2(g)  2 H2O(g)
Discovery of Cathode Ray
• In 1895, J.J. Thomson discovered cathode-ray
while studying the flow of electric current
through a vacuum.
Cathode-ray Tube used by J.J. Thomson
Cathode Ray
Characteristics of Cathode Ray
1. The ray originates from the cathode plate;
2. It is composed of negatively charged particles it bends in an electric or a magnetic field in the
direction similar to negatively charged particles;
3. The charge-to-mass ratio of the cathode ray
particles is constant at -1.76 x 108 C/g, regardless of
the materials used as the cathode;
4. Conclusion: cathode ray is a beam of negatively
charged particles that we now called electron.
Modern Version of Cathode-ray Tube
Thomson’s Model of Atom
• J.J. Thomson proposed the “Plum-pudding”
model:
(a) Atom is composed of a diffused mass (like a
cotton ball) of positive charge, with electrons
loosely embedded on its surface;
(b) The number of electrons present is such that
the total negative charge is equal to the magnitude
of positive charges in the atom.
Plum-Pudding Model
Alpha Particles Scattering Experiment
Rutherford’s Nuclear Model
Rutherford’s Atomic Model
• The Nuclear Model:
1. Atom contains nucleus, composed of protons and
neutrons;
2. The nucleus is much, much smaller than the atom;
3. Electrons occupy the vast “empty space” surrounding
the nucleus;
4. The mass of atom is concentrated in the nucleus;
5. Proton or neutron is almost 2000 times larger and
more massive than electron;
The Atomic Structure & Composition
A Version of Nuclear Model of Atom
Millikan’s Oil-Drop Experiments
Relative and Absolute Masses
• Proton: 1.007276 amu; 1.673 x 10-27 kg.
• Neutron: 1.008665 amu; 1.675 x 10-27 kg.
• Electron: 0.000549 amu; 9.109 x 10-31 kg.
Relative and Absolute Charges
• Proton = +1;
+1.602 x 10-19 C;
• Neutron = 0;
• Electron = -1;
-1.602 x 10-19 C;
Isotopes
1. Atoms of the same element that have
different masses;
2. Atoms having the same number of protons
but different number of neutrons;
3. Atoms with the same atomic number (Z) but
different mass number (A);
Atomic number (Z) = number of protons;
Mass number (A) = # of protons + # of neutrons;
Number of neutrons = (A – Z)
Exercise #2: Isotope Symbols
Write the symbols of isotopes that contain the
following:
(a) 10 protons, 10 neutrons, and 10 electrons.
(b) 12 protons, 13 neutrons, and 10 electrons.
(c) 15 protons, 16 neutrons, and 15 electrons.
(d) 17 protons, 18 neutrons, and 18 electrons.
(e) 24 protons, 28 neutrons, and 21 electrons.
(a) 20Ne; (b) 25Mg2 +; (c) 31P; (d) 35Cl-; (e) 52Cr3+
Exercise #3: Isotopes
Indicate the number of protons, neutrons, and
electrons in each isotope with the following symbols.
(a)
60
Ni
(b) 239Pu4+
(c) 79Se2-
Answers:
(a) 28 protons, 32 neutrons, and 28 electrons;
(b) 94 protons, 145 neutrons, and 90 electrons;
(c) 34 protons, 45 neutrons, and 36 electrons.
Molecules and Ions
• Molecule:
A neutral particle that contains two or more atoms
bound together (chemically) by covalent bonds.
• Ion:
Electrically charged particle, either positive (called
cation) or negative (called anion)
An atom may lose one or more electrons to form a
cation, or may gain electrons to form anions.
Periodic Table
• The modern Periodic Table is divided into 18
columns (groups) and 7 rows (periods).
• Groups are numbered 1 – 18 in the IUPAC
configuration, or 1A – 8A and 1B – 8B in the
ACS configuration.
• In each period, elements are arranged left-toright in increasing atomic number;
• Within each group, elements share similar
chemical and physical characteristics.
Periodic Table
Classification of Elements in The Periodic Table
Major Classifications of Elements
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Main group elements:
1.
2.
3.
4.
5.
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Group 1A (1): the alkali metals;
Group 2A (2): the alkaline Earth metals;
Groups 3A (13), 4A (14), 5A (15), and 6A (16),
Group 7A (17): the halogens, and
Group 8A (18): the noble gases.
Transition metals:
Groups 3B (3) – 2B (12) ; contains heavy metals.
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Metalloids (semi-metals):
B, Si, Ge, As, Sb, Te, Po, At
Characteristics of Metals and Nonmetals
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Metals:
1. Mainly solid, except for mercury; have shiny appearance;
2. Good conductors of heat and electricity;
3. Malleable and ductile;
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Nonmetals:
1. Mainly gases, one (bromine) is a liquid, and a few solids;
2. Generally poor conductors of electricity;
3. Solids are generally brittle and not lustrous.
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Metalloids (semi-metals):
1. Very hard (covalent network) solids;
2. physically look like metals, but chemically behave like
nonmetals;
More on Classifications of Elements
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Lanthanide series:
Elements after lanthanum (La): Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu;
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Actinide series:
1. Elements after actinium (Ac): Th, Pa, U, Pu, Am,
Cm, Bk, Cf, Es, Fm, Md, No, and Lr;
2. Mostly synthesized in particle accelerators and
all are radioactive;
Nomenclature
• Type-I (ionic) compounds:
contain cations with fixed charges: Group 1 and Group 2
metals, and aluminum.
• Type-II (ionic) compounds:
contain cations with variable charges: transition metals, In,
Sn, Tl, Pb, or any metals from the lanthanide or actinide
series.
• Type-III (molecular) compounds:
contain only nonmetals or metalloids and nonmetals;
Type-I (Ionic) Compounds
• Binary compounds:
NaCl: sodium chloride;
MgF2: magnesium fluoride;
Al2O3: aluminum oxide;
• Compounds containing polyatomic ions:
CaSO4: calcium sulfate;
NaHCO3: sodium hydrogen carbonate;
KNO3: potassium nitrate
Type-II (Ionic) Compounds
• Binary compounds:
FeCl2: iron(II) chloride;
CrO: chromium(II) oxide;
FeCl3: iron(III) chloride;
Cr2O3: chromium(III) oxide;
• Compounds containing polyatomic ions:
Co(NO3)2: cobalt(II) nitrate;
Co(NO3)3: cobalt(III) nitrate;
Pb(C2H3O2)2: lead(II) acetate;
Pb(C2H3O2)4: lead(IV) acetate;
Type-II Compounds Naming System
Formula
CrO
Cr2O3
Stock System
Old System
chromium(II) oxide
chromous oxide
chromium(III) oxide chromic oxide
Fe(NO3)2 Iron(II) nitrate
Fe(NO3)3 Iron(III) nitrate
Ferrous nitrate
Ferric nitrate
Exercise #4: Formula
Write the formulas of the following compounds:
(a) Aluminum nitrate
(b) Barium chromate
(c) Magnesium carbonate
(d) Iron(III) chloride
(e) Lead(II) acetate
(f) Nickel(II) sulfate hexahydrate
Exercise #4 Answers
(a) Aluminum nitrate = Al(NO3)3
(b) Barium chromate = BaCrO4
(c) Magnesium carbonate = MgCO3
(d) Iron(III) chloride = FeCl3
(e) Lead(II) acetate = Pb(C2H3O2)2
(f) Nickel(II) sulfate hexahydrate = NiSO46H2O
Exercise #5: Nomenclature
Name the following compounds:
(a) Ca(OH)2
(b) Cr(NO3)3
(c) FeSO4
(d) NaHCO3
(e) KH2PO4
(f) CuCl22H2O
Exercise #5 Answers
(a) Ca(OH)2 = Calcium hydroxide
(b) Cr(NO3)3 = Chromium(III) nitrate
(c) FeSO4 = Iron(II) sulfate
(d) NaHCO3 = Sodium hydrogen carbonate
(e) KH2PO4 = Potassium dihydrogen phosphate
(f) CuCl22H2O = Copper(II) chloride dihydrate
Naming Binary Acids
(Acids without oxygen in the formula):
Hydro + first syllable of anion + ic acid
HF = hydrofluoric acid (weak)
HCl = hydrochloric acid (strong)
HBr = hydrobromic acid (strong)
HI = hydroiodic acid (very strong)
H2S = hydrosulfuric acid (weak)
HCN = hydrocyanic acid (very weak)
Naming Oxoacids
Acids with oxygen in the formula:
Examples:
HNO3 – nitric acid (strong)
HNO2 – nitrous acid (weak)
H2SO4 – sulfuric acid (strong)
H2SO3 – sulfurous acid (weak)
H3PO4 – phosphoric acid (weak)
H3PO3 – phosphorous acid (very weak)
HC2H3O2 - acetic acid (weak)
More on Oxoacids
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HClO – hypochlorous acid (very weak)
HClO2 – chlorous acid (weak)
HClO3 – chloric acid (moderate)
HClO4 – perchloric acid (very strong)
HBrO4 – perbromic acid (strong)
HIO4 – periodic acid (strong)
Exercise #6: Acid Nomenclature
Name the following oxo-acids:
(a) H2CO3
(b) H2CrO4
(c) HBrO
(d) HBrO2
(e) HBrO3
(f) HIO2
(g) HIO3
(h) HIO4
Exercise #6 Answers
(a) H2CO3 = Carbonic acid
(b) H2CrO4 = Chromic acid
(c) HBrO = Hypobrobous acid
(d) HBrO2 = Bromous acid
(e) HBrO3 = Bromic acid
(f) HIO2 = Iodous acid
(g) HIO3 = Iodic acid
(h) HIO4 = Periodic acid