Download Chapter 2 - Chemistry

Chapter 2
(Essentials of General Chemistry, 2nd Edition)
(Ebbing and Gammon)
Atoms, Molecules
and Ions
Atomic Theory of Matter
John Dalton (British Chemist)
- basic theory of modern chemistry
- all matter whether element, compound or
mixture is composed of small particles called
atoms
- purpose of atomic theory:
to provide explanation of the structure of
matter in terms of different combinations
of very small particles
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Postulates of Dalton s Atomic Theory
1.) All matter is composed of indivisible atoms. An atom is
an extremely small particle of matter that retains its
identity during chemical reactions.
2.) An element is a type of matter composed of only one
kind of atom, each atom of a given kind having the same
properties.
3.) A compound is a type of matter composed of atoms of
two or more elements chemically combined in fixed
proportions.
4.) A chemical reaction consists of the rearrangement of
the atoms present in the reacting substances to give new
chemical combinations present in the substances formed
by the reaction.
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Atomic Symbols and Models
Atomic symbol
- a one- or two-letter notation used to represent an
atom corresponding to a particular element
- convention: first letter capital
second letter lowercase
- origin: from the name of the element
from a name in another language (Latin)
Atomic Models
- Dalton used spheres to represent atoms and used
combinations of these spheres to represent
compounds
- still used today but more refined
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Representations of Molecules
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Deductions from Dalton s Atomic Theory
Explains:
1.) difference between element and compound
2.) Law of Mass Conservation
- states that total mass remains constant
during a chemical reaction
3.) Law of Definite Proportions
- compound is type of matter containing
atoms of two or more elements is definite
proportions
4.) Law of Multiple Proportions
- when two elements form more than one compound,
the masses of one element in these compounds for a
fixed mass of the other element are in rations of
small whole numbers
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The Structure of the Atom
Two Particles:
1.) nucleus (atom s central core)
- positively charged
- contains most of atoms mass
2.) electron (outside atom s central core)
- negatively charged
- very light
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Discovery of the Electron
Cathode-ray Tube (J. J. Thomson- 1897)
- used experimental apparatus to conclude that
cathode ray consists of beam of negatively charged
particles (or electrons)
charge-to-mass ratio calculation (e/m)
- ratio of e- electric charge to its mass
modern (excepted value):
e/m = 1.758820 x 108 C/g
e = magnitude of charge of e- in coulombs (C)
m = mass of e- in grams
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A Cathode-ray Tube
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Measuring the Mass of an Electron
Oil-drop Experiment (Robert A. Millikan 1909)
- experiment used to obtain the charge on an
electron (1.602 x 10-19 coulombs)
- using charge-to-mass ratio (by Thomson)
e = 1.758820 x 108 C/g
m
then
m=
e
= 1.602176 x 10-19 C
8
1.758820 x 10 g/C
1.758820 x 108 C/g
= 9.109382 x 10-28 g
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Millikan s Oil-drop Experiment
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Nuclear Model of Atom
Ernest Rutherford (British Physicist - 1911)
- proposed that metal atom he was studying
must be almost entirely empty space with
mass concentrated in tiny central core
- showed that atoms consisted of a positively
charged nucleus at the center of the atom,
around which negatively charged electrons
move
- nucleus occupies only very small portion of
space of atom
nuclei diameters
10-3 picometers
atomic diameters
100 picometers
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The Rutherford Scattering Experiment
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Nuclear Structure: Isotopes
Structure of Nucleus:
1.) proton
-a nuclear particle
having a positive
charge equal to that
of the electron and
has a mass more than
1800 times that of the
electron
2.) neutron
- a nuclear particle having a mass almost
identical to that of the proton but no electric
charge
Note: characterize nucleus by atomic number (Z) and
mass number (A)
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Atomic Composition
atomic number (Z)
- number of protons in nucleus of an atom
- charge of nucleus of particular atom is equal to number
of protons
element
substance whose atoms all have the same atomic
number
atomic number (Z) = number of protons
mass number (A)
- total number of protons and neutrons in a nucleus
A = number of protons + number of neutrons
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Atomic Composition: Nuclear Symbol
nuclide
atom characterized by a definite atomic number
and mass number
atomic no. - subscript at lower left of the element
symbol
mass no. - superscript at upper left of the element
symbol
A X
Z
where: X = element symbol
A = mass number
Z = atomic number
isotopes atoms whose nuclei have the same atomic
number but different mass numbers (ie. nuclei
have the same number of protons but different
numbers of neutrons)
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Atomic Mass Units
mass spectrometer
- instrument to measure relative atomic masses
atomic mass unit (amu)
- convenient unit used for reporting mass of atoms
- mass of atom is compared to a carbon-12 isotope which
is assigned a mass of exactly 12 atomic mass units (amu)
- therefore, 1 amu = 1/12 mass of a carbon-12 atom
atomic mass (of an element)
- the average atomic mass for the naturally occurring
element, expressed in atomic mass units
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Diagram of a Simple Mass Spectrometer
Figure 2.8: Showing the Separation of Neon Isotopes
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Periodic Table of the Elements
Dmitri Mendeleev and J. Lothar Meyer
- tabular arrangement of elements in rows and
columns, highlighting the regular repetition of
properties of the elements
- today arrangement of elements by atomic number
(represents element by symbol, atomic number and
atomic mass)
Organization of the periodic table
A.) i.) periods consists of elements in any one horizontal
row of periodic table
ii.) groups consists of elements in any one column of
periodic table
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A modern form of the periodic table
Figure 2.11
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Numbers and Labels
Two systems:
1.) labels the groups with Roman numerals and A s
and B s
i.) North America (IA)
ii.) Europe (AI)
Categories within periodic table:
- main-group elements: A groups
- transition elements: B groups
- inner-transition elements:
lanthanides (1st row)
actinides (2nd row)
2.) International Union of Pure and Applied Chemistry
(IUPAC) has convention with columns numbered 1
to 18
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Similarity in Chemical Properties
Group 1A (Alkali metals)
- shiny and soft
- react violently with H2O
- not found in nature in pure
form (highly reactive)
- exception - hydrogen
Group 7A (Halogens)
-colorful, corrosive
nonmetals
- found in nature only in
combination with other
elements
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Metals, Nonmetals and Metalloids
Categories:
i.) metals
- substance or mixture that has a characteristic luster
(ie. silvery shine)
- all solid at R.T. (except mercury (Hg))
- generally malleable and ductile rather than brittle
(easily shaped)
- good conductors of heat and electricity
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ii.) nonmetals
- element that does nor exhibit the characteristic of a
metal
- eleven gases, one liquid (Br), five solids (C, P, S, Se, I)
- many are brightly colored but none are silvery
- solids are hard and brittle rather than malleable
- poor conductors of heat and electricity
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iii.) semimetal (metalloid)
- border staircase line in periodic table (seven of nine
elements adjacent to boundary between metals and
nonmetals and include B, Si, Ge, As, Sb, Te, At)
- properties intermediate btw metals and nonmetals
- semiconductors (eg. silicon and germanium)
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Chemical Formulas
Molecular and Ionic Substances:
chemical formula
- notation that uses atomic symbols with numerical
subscripts to convey the relative proportions of atoms
of the different elements in the substance
- no subscript - the number 1 is understood
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Molecular Substances
molecule
definite group of atoms that are chemically bonded
together
molecule substance
substance composed of molecules that are all alike
molecular formula
gives exact number of different atoms of an element in
a molecule
structural formula
chemical formula that shows how atoms are bonded to
one another
- sometimes condensed in writing
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molecular models
- atoms in molecule mot only connected in definite ways
but exhibit spatial arrangements as well
- ball-and-stick and space-filling models
Note: - some elements have simple formulas
- some elements consist of very large, indefinite
number of atoms bonded together
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Molecular and Structural Formulas and Molecular Models
Figure 2.12
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Class of Molecular Substances
monomers
small molecules that are linked together to form
polymers
polymers
- very large molecules that are made up of a number of
smaller molecules repeatedly linked
i.) natural wool and silk
ii.) synthetic Nylon, Kevlar, Nomex, Teflon
- plastics and rubbers
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Organic Compounds
- class of molecular substances that contain carbon
combined with other elements, such as hydrogen,
oxygen and nitrogen
hydrocarbon
- simplest organic compounds
- those compounds containing only hydrogen and carbon
- extensively used as sources of energy
- starting materials for plastics
functional group
- reactive portion of a molecule that undergoes
predictable reactions
- determines chemistry of organic molecules
inorganic compounds
- composed of elements other than carbon
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Some Organic Functional Groups
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Ionic Substances
ion
an electrically charged particle obtained from an atom
or molecule by adding or removing electrons
i.) anion negatively charged ion
- atom that picks up extra electron(s)
- nonmetals tend to gain electron(s)
ii.) cation positively charged ion
- atom that loses electron(s)
- metal atoms tend to lose electron(s)
Note: ions may consist of two or more atoms chemically
bonded but having an excess or deficiency of
electron(s)
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Ionic Compounds
ionic compound
compound composed of cations and anions
- held together by strong attraction between positive
(+ve) and negative (-ve) charges
- always written by giving smallest possible integer
number of different ions in a substance
formula unit
the group of atoms or ions explicitly symbolized in
formula
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Naming Simple Compounds
chemical nomenclature
- systematic naming of chemical compounds
Ionic Compounds
- substances composed of ions
- positive ion name (metal) is given first followed by
the name of the negative ion (nonmetal)
Types of ions:
i.) monatomic ion
- an ion formed from a single atom
ii.) polyatomic ion
- an ion consisting of two or more atoms
chemically bonded together and carrying a
net electric charge
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Monatomic Ions
Predicting the Charges of Monatomic Ions
1.) Most of the main-group metallic elements have one
monatomic cation with a charge equal to the group
number in the periodic table (the Roman numeral)
2.) Some metallic elements have more than one cation.
These elements have common cations with a charge
equal to the group number minus 2, in addition to
having a cation with a charge equal to the group
number.
3.) Most transition elements form more than one cation.
Most of these elements have one ion with a charge of +2.
4.) The charge on a monatomic anion for a nonmetallic
main group element equals the group number minus 8.
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Main-group cations
and anions
Common transition
metals ions
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Naming Monatomic Ions
1.) Monatomic cations are names after the element. If
there is more than one monatomic cation of an element,
a Roman numeral in parentheses is used to denote the
charge on the ion.
2.) The names of monatomic anions are obtained from a
stem name of the element followed by the suffix ide.
Table 2.5
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Polyatomic Ions
cations mercury (I) cation and ammonium cation
anions
i.) oxoanions (oxyanions)
- consist of oxygen with another element
-named with stem name from nonmetal element and
a.) for element that forms two oxoanions
- suffix -ate - oxoanion with greater no. of O
- suffix -ite - oxoanion with fewer no. of O
b.) for element that forms more than two oxoanions
- prefix per- - oxoanion with largest no. of O
- prefix hypo- -oxoanion with fewest no. of O
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ii.) acid anions
- oxoanions bonded to one or more hydrogen
ions (H+)
iii.) thiosulfate ion
- root ion SO42- (sulfate); thio- means an oxygen
atom has been replaced by a sulfur
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Common Polyatomic Ions
Table 2.6
Table 2.6
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Binary Molecular Compounds
Binary compound
compound composed of only two elements
i.) ionic compound
composed of metal and nonmetal
ii.) binary molecular compound
two nonmetals or metalloids named using
prefix system
- usually named using the order given in
formula (nonmetals and metals approximately
in order of increasing nonmetallic character)
a.) 1st element more metallic
b.) 2nd element more nonmetallic
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Naming Binary Molecular Compounds
1.) Name of compound usually has elements in
order given in formula.
2.) Name the first element using the exact element
name.
3.) Name the second element by writing the stem
name of the element with the suffix ide.
4.) Add prefix, derived from the Greek, to each element
name to denote subscript of element in formula.
Note: generally, prefix mono- is not used, unless needed to
distinguish two compounds of the same two elements
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Greek Prefixes
Table 2.7
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Acids and Anions
acid
molecular compound that yields hydrogen
ions, H+, and an anion for each acid molecule
when the acid dissolves in water
oxoacids
- acid containing hydrogen, oxygen and another
element
- when dissolved in water, an oxoacid yields one or
more H+ ions and polyatomic oxoanions
- named as related to oxoanions:
i.) -ate suffix replaced by -ic acid
ii.) -ite suffix replaced by -ous acid
iii.) per- and hypo- prefixes are retained
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Oxoanions and Oxoacids
Table 2.8
Table 2.8
46
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Binary Molecular Compounds
- binary compounds of hydrogen and nonmetals yield
acidic solutions when dissolved in water
- name these solutions using the prefix hydro- and
suffix ic with the stem name of the nonmetal, followed
by the word acid
- denote solution by formula of binary compound
compound followed by (aq) aqueous (water ) solution
HCl(g)
dissolves in water
HCl (aq) (H+, Cl-)
hydrogen chloride
HBr(g)
hydrochloric acid
dissolves in water
HBr (aq) (H+, Br-)
hydrogen bromide
hydrobromic acid
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Hydrates
- compound that contains water molecules weakly bound
in its crystal
- named from the anhydrous compound followed by the
word hydrate with a prefix to indicate the number of
water molecules per formula unit of the compound
eg. CuSO4·5H2O
copper (II) sulfate pentahydrate
- anhydrous substance in copper (II) sulfate
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Writing Chemical Equations
chemical equation
symbolic representation of a chemical reaction in
terms of chemical formulas
i.) reactants formulas on left side of equation
ii.) products formulas on right side of equation
iii.) arrow reacts to form or yields
coefficients
number in front of formula give relative number of
formula units involved in reaction
(Note: coefficient of 1 is understood, not written)
states or phases of substances
indicated using labels
(g) gas, (l) liquid, (s) solid, (aq) - aqueous
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Symbols over the reaction arrow:
i.) if reactants are heated to make a reaction go, place
the Greek symbol delta ( ) over the arrow
2 NaNO3 (s)
2 NaNO2 (s) + O2 (g)
ii.) catalyst a substance that speeds up a reaction
without undergoing any net change itself
- the element symbol of the catalytic
substance is often placed over the arrow
2 H2O2 (aq)
Pt
2 H2O (l) + O2 (g)
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Balancing Chemical Equations
balanced
numbers of atoms of each element are equal on
both sides of the arrow (this is achieved when
coefficients in chemical equation are given
correctly)
chemical reaction
recombination of atoms; none are destroyed and
none are created
Note: 1.) write the coefficients so that they are the smallest
whole numbers possible
2.) balance first the atoms for elements that occur in
only one substance on each side of the equation
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