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The Atomic Theory of
Matter
• John Dalton:
– Each element is composed of atoms
– All atoms of an element are identical.
– In chemical reactions, the atoms are not
changed.
• Compounds are formed when atoms of more
than one element combine.
• Dalton’s law of multiple proportions: When
two elements form different compounds, the
mass ratio of the elements in one compound
is related to the mass ratio in the other by a
small whole number.
The Discovery of Atomic
Structure
• The ancient Greeks were the first to postulate that matter
consists of indivisible constituents.
• Later scientists realized that the atom consisted of
charged entities.
Cathode Rays and Electrons
• A cathode ray tube (CRT) is a hollow vessel with an
electrode at either end.
• A high voltage is applied across the electrodes.
The voltage causes negative particles to move from the
negative electrode to the positive electrode.
• The path of the electrons can be altered by the presence of a
magnetic field.
Cathode Rays and Electrons
– The amount of deflection of the cathode rays depends
on the applied magnetic and electric fields.
– In turn, the amount of deflection also depends on the
charge to mass ratio of the electron.
• In 1897, Thomson determined the charge to mass ratio of
an electron to be 1.76  108 C/g.
• Goal: find the charge on the electron to determine its
mass.
The Discovery of Atomic
Structure
Cathode Rays and Electrons
The Discovery of Atomic
Structure
Cathode Rays and Electrons
Consider the following experiment:
• Oil drops are sprayed above a positively charged plate
containing a small hole.
• As the oil drops fall through the hole, they are given a
negative charge.
• Gravity forces the drops downward. The applied electric
field forces the drops upward.
• When a drop is perfectly balanced, the weight of the drop
is equal to the electrostatic force of attraction between the
drop and the positive plate.
The Discovery of Atomic
Structure
Cathode Rays and Electrons
Charge and mass of electrons
….
• Using this experiment, Millikan determined the charge on
the electron to be 1.60  10-19 C.
• Knowing the charge to mass ratio, 1.76  108 C/g,
Millikan calculated the mass of the electron: 9.10  10-28
g.
• With more accurate numbers, we get the mass of the
electron to be 9.10939  10-28 g.
Radioactivity
Products of decay
Radioactivity
The Discovery of Atomic
Structure
The Nuclear Atom
• From the separation of
radiation we conclude that
the atom consists of neutral,
positively, and negatively
charged entities.
• Thomson assumed all these
charged species were found
in a sphere.
Rutherford carried out the following experiment
Conclusion: Nuclear Atom
• In order to get the majority of -particles through a piece
of foil to be undeflected,
• 1. the majority of the atom must consist of a low mass,
• 2. diffuse negative charge - the electron.
• To account for the small number of high deflections of
the -particles
• 3. the center or nucleus of the atom must consist of a
dense positive charge.
• Rutherford modified
Thomson’s model as follows:
– assume the atom is spherical
but the positive charge must
be located at the center, with
a diffuse negative charge
surrounding it.
Atomic Theory of Matter
• Nuclear structure; Isotopes
The nucleus of an atom is composed of two different
kinds of particles: protons and neutrons.
An important property of the nucleus is its positive
electric charge.
A proton is the nuclear particle having a positive
charge equal to that of the electron’s (a “unit”
charge) and a mass more than 1800 times that of
the electron’s
The number of protons in the nucleus of an
atom is referred to as its atomic number (Z).
An element is a substance whose atoms all have the
same atomic number.
The neutron is a nuclear particle having a mass
almost identical to that of a proton, but no electric
charge.
The mass number is the total number of
protons and neutrons in a nucleus.
A nuclide is an atom characterized by a definite
atomic number and mass number.
The shorthand notation for a nuclide consists of
its symbol with the atomic number as a
subscript on the left and its mass number as a
superscript on the left.
sodium - 23
23
11 Na
Isotopes are atoms whose nuclei have the same atomic
number but different mass numbers; that is, the
nuclei have the same number of protons but different
numbers of neutrons.
Chlorine, for example, exists as two isotopes: chlorine35 and chlorine-37.
35
37
17 Cl
17 Cl
The fractional abundance is the fraction of a sample of
atoms that is composed of a particular isotope.
Mass Spectrophotometer
Gas Chromatography Mass Spectrometry: How Does It Work?
Atomic Weights
Calculate the atomic weight of boron, B, from
the following data:
ISOTOPE
B-10
B-11
ISOTOPIC MASS (amu)
10.013
11.009
FRACTIONAL ABUNDANCE
0.1978
0.8022
Atomic Weights
Calculate the atomic weight of boron, B, from
the following data:
ISOTOPE
B-10
B-11
ISOTOPIC MASS (amu)
10.013
11.009
FRACTIONAL ABUNDANCE
0.1978
0.8022
B-10: 10.013 x 0.1978 = 1.9805
B-11: 11.009 x 0.8022 = 8.8314
10.8119 = 10.812 amu
( = atomic wt.)
Atomic Weights
• Dalton’s Relative Atomic Masses
Since Dalton could not weigh individual atoms,
he devised experiments to measure their masses
relative to the hydrogen atom.
Hydrogen was chosen as it was believed to be
the lightest element. Daltons assigned hydrogen
a mass of 1.
For example, he found that carbon weighed 12
times more than hydrogen. He therefore
assigned carbon a mass of 12.
Atomic Weights
• Dalton’s Relative Atomic Masses
Dalton’s atomic weight scale was eventually
replaced in 1961, by the present carbon–12 mass
scale.
One atomic mass unit (amu) is, therefore, a mass
unit equal to exactly 1/12 the mass of a carbon–12
atom.
On this modern scale, the atomic weight of an
element is the average atomic mass for the naturally
occurring element, expressed in atomic mass units.
The Periodic Table
The Periodic Table
• Some of the groups in the periodic table are given special
names.
• These names indicate the similarities between group
members:
Group 1A: Alkali metals.
Group 2A: Alkaline earth metals.
Group 6A: Chalcogens.
Group 7A: Halogens.
Group 8A: Noble gases.
Molecules and Molecular
Compounds
Molecules and Chemical Formulas
• Molecules are assemblies of two or more atoms bonded
together.
• Each molecule has a chemical formula.
• The chemical formula indicates
– which atoms are found in the molecule, and
– in what proportion they are found.
• Compounds formed from molecules are molecular
compounds.
• Molecules that contain two atoms bonded together are
called diatomic molecules.
Diatomic molecules
Molecules and Molecular
Compounds
Molecular and Empirical Formulas
• Molecular formulas
Molecular and Empirical
Formulas
• Empirical formulas
– give the relative numbers and types of atoms in a
molecule.
– the lowest whole number ratio of atoms or moles
of atoms in a molecule
– Examples: H2O, CO2, CO, CH4, HO, CH2.
– 2 atoms of hydrogen / 1 atom of oxygen
– 2 moles of hydrogen / I mole of oxygen
Chemical Formulas
Molecular and Ionic Substances
• The chemical formula of a substance is a
notation using atomic symbols with subscripts to
convey the relative proportions of atoms of the
different elements in a substance.
Consider the formula of aluminum oxide, Al2O3.
This formula implies that the compound is
composed of aluminum atoms and oxygen atoms
in the ratio 2:3.
• Molecular substances
A molecule is a definite group of atoms that are
chemically bonded together – that is, tightly connected
by attractive forces.
A molecular substance is a substance that is composed
of molecules, all are nonmetals.
A molecular formula gives the exact number of
atoms of elements in a molecule.
Structural formulas show how the atoms are
bonded to one another in a molecule.
• Ionic substances
An ion is an electrically charged particle obtained from
an atom or chemically bonded group of atoms by
adding or removing electrons.
Anion 
Cation 
The formula of an ionic compound is written by
giving the smallest possible whole-number ratio of
different ions in the substance.
Empirical formula
The formula unit of the substance is the group of
atoms or ions explicitly symbolized by its formula.
• Naming simple compounds
Chemical compounds are classified as organic or
inorganic.
Organic compounds are compounds that contain carbon
combined with other elements, such as hydrogen,
oxygen, and nitrogen.
Inorganic compounds are compounds composed
of elements other than carbon.
Ionic = inorganic
Most ionic compounds contain metal and
nonmetal atoms; for example, NaCl.
You name an ionic compound by giving the name
of the cation followed by the name of the anion.
• Rules for predicting charges on
monatomic ions
Most of the main group metals form cations with the
charge equal to their group number.
Most transition elements form more than one ion,
each with a different charge.
Ions and Ionic Compounds
Predicting Ionic Charge
Chemical Substances;
Formulas and Names
• Rules for naming monatomic ions
Monatomic cations are named after the element.
For example, Al3+ is called the aluminum ion.
If there is more than one cation of an element, a
Roman numeral in parentheses denoting the
charge on the ion is used.
usually transition elements.
The names of the monatomic anions use the stem
name of the element followed by the suffix – ide.
For example, Br- is called the bromide ion.
Naming Binary Compounds
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NaF
LiCl
MgO
CaS
AlP
KI
RbCl
CsBr
BaO
SrS
-
Chemical Substances;
Formulas and Names
• Polyatomic ions
A polyatomic ion is an ion consisting of two or
more atoms covalently bonded together and
carrying a net electric charge.
Cations formed from non-metals end in -ium.
Example: NH4+ ammonium ion.
-
NO 3 nitrate
-
NO 2 nitrite
2-
SO 4 sulfate
2-
SO 3 sulfite
Ions You Should Know
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NH4+ - Ammonium
OH- - Hydroxide
CN- - Cyanide
SO42- - Sulfate
ClO4- - Perchlorate
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O22- - Peroxide
PO43- - Phosphate
CO32- - Carbonate
HCO3- - Bicarbonate
Plus what is on your
“stuff you should
know for the AP test
sheet”
Oxy anions
• General rule:
• If there are two oxyion forms of an anion
– NO2 and NO3
– the one with the most oxygen ends in –ate
– If that anion forms an acid the –ate is changed to –ic
• Ic I ate it all! Refers to the concept that –ate has
all of the oxygens (the most)
– NO3  nitrate ion  HNO3 Nitric Acid
– The lower oxygenated ion ends with –ite and forms
an acid that ends with –ous
– NO2  Nitrite ion  HNO2 Nitrous Acid
More than two forms of oxy ions?
• If there are more than two forms then the
prefixes
– Hyper and Hypo are used
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•
•
•
ClO4ClO3ClO2ClO-
HyperChlorate ion
Chlorate ion
Chlorite ion
Hypochlorite ion
Polyatomic anions containing oxygen
with additional hydrogens
• named by adding
• hydrogen or bi- (one H), dihydrogen (two H), etc., to
the name as follows:
CO32- is the carbonate anion
HCO3- is the hydrogen carbonate (or bicarbonate) anion.
H2PO4- is the dihydrogen phosphate anion.
NaHCO3 Sodium bicarbonate
Binary molecular compounds
Binary compounds composed of two nonmetals are
usually molecular and are named using a prefix
system.
The name of the compound has the elements in the
order given in the formula.
You name the first element using the exact element
name.
Name the second element by writing the stem name
of the element with the suffix “–ide.”
If there is more than one atom of any given element,
you add a prefix.
Here are some examples of prefix names for binary
molecular compounds.
SF4
sulfur tetrafluoride
• ClO2 chlorine dioxide
SF6
sulfur hexafluoride
Cl2O7 dichlorine heptoxide
Acids
Acids are traditionally defined as compounds with a
potential H+ as the cation.
Binary acids consist of a hydrogen ion and any single
anion. For example, HCl is hydrochloric acid.
An oxoacid is an acid containing hydrogen, oxygen,
and another element. An example is HNO3, nitric
acid.
Hydrates
A hydrate is a compound that contains water molecules
weakly bound in its crystals.
Hydrates are named from the anhydrous (dry) compound,
followed by the word “hydrate” with a prefix to
indicate the number of water molecules per formula
unit of the compound.
CuSO4. 5H2O = copper(II)sulfate pentahydrate.
Some Simple Organic
Compounds
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Alkanes
Organic chemistry: the study of the chemistry of carbon
compounds.
Alkanes contain only C and H and are called
hydrocarbons.
The names of alkanes all end in the suffix –ane.
Alkanes are named according to the number of C atoms
in their backbone chain:
• Methane has one C atom (CH4)
• Ethane has two C atoms (CH3CH3)
• Propane has three C atoms (CH3CH2CH3), etc.
Some Simple Organic
Compounds
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Some Derivatives of Alkanes
When H atoms in alkanes are replaced by heteroatoms
(atoms other than C or H), then we have introduced a
functional group into the alkane.
When an H is replaced by –OH, then we form an alcohol.
Alcohols are also named by the number of C atoms.
Consider propanol: there are two places for the OH: on
an end C or the middle C.
• When the OH is located on the end C, we call the
substance 1-propanol.
• When the OH is on the middle C, we have 2-propanol.
Some Simple Organic
Compounds
Some Derivatives of Alkanes
• When the single bonds in an alkane are replaced by one
or more double bonds, then we form alkenes.
• When a double bond is formed between C and O, we
form carboxylic acids, ketones, aldehydes, and esters.
• Any organic molecule with double or triple bonds is
called unsaturated.
Chemical Reactions:
Equations
• Writing chemical equations
A chemical equation is the symbolic representation
of a chemical reaction in terms of chemical formulas.
For example, the burning of sodium and chlorine to
produce sodium chloride is written
2Na  Cl 2  2NaCl
The reactants are starting substances in a chemical
reaction. The arrow means “yields.” The formulas on
the right side of the arrow represent the products.
Writing chemical equations
The law of conservation of mass dictates that the total
number of atoms of each element on both sides of a
chemical equation must match. The equation is then
said to be balanced.
CH4 
O 2  CO2 
H 2O
Consider the combustion of methane to produce
carbon dioxide and water.
Balance the following equations.
O2 
P4 
PCl 3 
N 2O 
As2S 3 
Ca3 (PO4 )2 
O2 
POCl 3
P4O6 
As2O 3 
H 3 PO 4 
N2
SO 2
Ca(H2 PO 4 )2