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Chapter 2
Atoms, Molecules, and Ions
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2.1
Atoms
Atomic theory : on the basis of Dalton’s theory
Components : proton, neutron, electron
Atomic Number : number of protons
Mass Number : number of protons and neutrons
Nuclear Stability : radioactivity
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2.2
Atomic Theory
Postulates
Elements consist of tiny particles called atoms which retain their
identity in reactions
In a compound, atoms of two or more elements are combined in a
fixed ratio of small whole numbers; e. g. 1:1, 2:1, etc.
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2.3
Some features of Dalton’s theory
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2.4
Some features of Dalton’s theory
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2.5
Cathode ray tube
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2.6
Rutherford’s scattering experiment
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2.7
Components
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2.8
Atomic Number
Atomic number
equals number of protons in nucleus
equals number of electrons in neutral atom
is a characteristic of a particular element
all H atoms have 1 proton, all He atoms have
2 protons, etc.
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2.9
Mass Number
Mass number
equals number of protons + number of neutrons
atoms of the same element can differ in mass number
protons
carbon-12
carbon-14
6
6
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neutrons
6
8
atomic
number
nuclear
symbol
mass
number
6
12
C
6
12
6
14
C
6
14
2.10
Nuclear Stability
Neutron-to-proton ratio increases with atomic number.
Unstable isotopes decompose by radioactivity. Ordinarily the
result is the transmutation of elements
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2.11
Nuclear Stability - Belt of stability
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2.12
Periodic table
Structure : period (horizontal rows) & group (vertical columns)
Metals, Nonmetals, & Metalloids
metal : high electrical conductivity
metalloid : intermediate electrical conductivity between
metal and nonmetal
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2.13
Structure
Periods : horizontal rows
Groups : vertical columns
numbering system for groups
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2.14
Metals, Nonmetals, Metalloids
Metals
About 80 elements
located at lower left of periodic table
Nonmetals
About 18 elements
located at upper right of periodic table
Metalloids
B, Si, Ge, As, Sb, Te
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2.15
Molecules
Composition : isolated atoms and combined atomes
Types of Formulas
molecular : number of atoms of each element is indicated by a
subscript written after the symbol of the element
structural : bonding pattern within the molecule
condensed structural : bonding pattern in the molecule and
highlights the presence of a reactive group
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2.16
Composition
Two or more atoms may combine with one another to form an
uncharged molecule. Usually nonmetal atoms made up
molecules.
Within the molecule, atoms are held together by covalent bonds
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2.17
Types of Formulas
Consider the molecule ethane
Molecular formula: C2H6
Structural formula:
H H
H C C H
H H
Condensed structural formula: CH3CH3
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( -CH3 is alkyl)
2.18
Molecular elements and their physical states
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2.19
Ions
Formation of Monatomic Ions
cation (positively charged), anion (negatively charged)
Charges of Monatomic Ions with noble-gas structure
atoms form ions that contain the same number of
electrons as the neighboring noble-gas atom
Polyatomic Ions
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2.20
Ions
Formulas of compounds
the total positive charge of the cations in the
formula must equal the total negative charge of
the anions
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2.21
Formation of Monatomic Ions
Formation
Cation : Na atom (11p+, 11e -) → Na+ ion (11p+, 11e -) + e Anion : F atom (9p+, 9e -) + e - → F - ion (9p+, 10e -)
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2.22
Charges of Monatomic Ions with noble-gas structures
Cation: Group 1 (+1); Group 2 (+2); Al3+
Anion: Group 16 (-2); Group 17 (-1); N3-
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2.23
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2.24
Formulas of compounds
Apply principle of electroneutrality
calcium fluoride: Ca2+, F- ions: CaF2
aluminum nitrate: Al3+, NO3- : Al(NO3)3
sodium dihydrogen phosphate:
Na+, H2PO4- : NaH2PO4
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2.25
Names of Compounds
Ionic : consist of two words – first names the cation and the
second names the anion
Binary Molecular Compounds : when two nonmetals combine
with each other, the product is most often a binary
molecular compounds
Acids : form H+ ions
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2.26
Ionic
Name cation followed by anion
Note that with transition metal cations, charge is indicated by
Roman numeral
Na2SO4
sodium sulfate
Fe(NO3)3 iron (III) nitrate
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2.27
Ionic (cont.)
Systematic names of oxoanions
-ate, -ite, per-, hypo-per (largest number of oxygen atoms) > -ate > -ite > -hype
Calcium hypochlorite: Ca(ClO)2
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2.28
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2.29
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2.30
Binary Molecular Compounds
The first word gives the name of the element that appears first
in the formula and the second. Greek prefixes are used to
show the number of atoms of that element in the formula
SF6
N2O3
sulfur hexafluoride
dinitrogen trioxide
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2.31
Acids
Binary Acids: containing H atoms ionize in water to form H+ ions
hydrochloric acid (HCl)
Oxoacids: simply related to those of the corresponding oxoanions
ate salt → ic acid
ite salt → ous acid
Examples:
HClO4
HClO
perchloric acid
hypochlorous acid
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2.32