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Chapter 2 — Atoms, Molecules, Ions
1
2
ATOMIC COMPOSITION
John C. Kotz
Paul M. Treichel
John Townsend
•  Protons
– 
– 
– 
http://academic.cengage.com/kotz
+ electrical charge
mass = 1.672623 x 10-24 g
relative mass = 1.007 atomic
mass units (u or amu)
•  Electrons
Chapter 2
Atoms, Molecules, and Ions
– 
– 
negative electrical charge
relative mass = 0.0005 u
•  Neutrons
– 
– 
no electrical charge
mass = 1.009 u
•  1 u = ? g
John C. Kotz • State University of New York, College at Oneonta
© 2009 Brooks/Cole - Cengage
3
ATOM
COMPOSITION
A, Z, Isotopes
The atom is mostly
empty space
•  protons and neutrons in
the nucleus.
PLAY MOVIE
•  the number of electrons is equal to the
number of protons.
10
Z
5
•  Atomic Number (Z) = # protons
•  Mass Number (A) = # protons + # neutrons
•  Isotopes are atoms of the same element (same Z)
but different mass number (A).
•  Boron-10 has 5 p and 5 n: 105B
•  Boron-11 has 5 p and 6 n: 115B
•  electrons in space around the nucleus.
11B
•  extremely small. One teaspoon of water
has 3 times as many atoms as the Atlantic
Ocean has teaspoons of water.
© 2009 Brooks/Cole - Cengage
A
10B
© 2009 Brooks/Cole - Cengage
4
B
Chapter 2 — Atoms, Molecules, Ions
Hydrogen Isotopes
1
1
H
1 proton + 0 neutrons,
protium
2
1
H
1 proton + 1 neutron,
deuterium
3
1
H
1 proton + 2 neutrons,
tritium
radioactive
2
5
6
Mass Spectrometer separates isotopes
© 2009 Brooks/Cole - Cengage
© 2009 Brooks/Cole - Cengage
7
Mass Spectrum
•  a mass spectrum is a graph that
gives the relative mass and
relative abundance of each
particle
•  relative mass of the particle is
plotted in the x-axis
•  relative abundance of the particle
is plotted in the y-axis
© 2009 Brooks/Cole - Cengage
8
% Abundance vs % by Weight
A charter school class has 6 girls, who each
weight 100 lbs, and 4 boys, who each weigh
150 lbs.
•  What is the % abundance of girls?
•  What is the average weight of the students?
•  What is the % by weight of girls?
•  Isotopic abundance tells % by count, not %
by weight
© 2009 Brooks/Cole - Cengage
Chapter 2 — Atoms, Molecules, Ions
3
9
Isotopes
10
Isotopes & Atomic Weight
11B
10B
•  Except for carbon-12 with mass = 12 u, isotopic masses are
not integer values. However they are very close to integers
•  Because of the existence of isotopes, the mass of a
collection of atoms has an average value.
– 
10B
= 10.0129 u and 11B = 11.0093 u
•  Actual masses of atoms are always less than the sum of the
masses of subatomic particles because of the mass defect
•  If isotope masses and abundances are known, calculate
atomic mass:
•  Average mass = ATOMIC WEIGHT or Atomic Mass
•  Boron is 19.9% 10B and 80.1% 11B. That is, 11B is 80.1
percent abundant on earth.
Atomic Mass = ∑ (fractional abundance of isotope)n × (mass of isotope)n
•  For boron atomic mass = 0.199(10.0 u) + 0.801 (11.0 u)
= 10.8 u
isotope 1 (mass of isotope 1)
( % abundance
)
100
isotope 2 ) (mass of isotope 2) + . . .
( % abundance
100
Atomic Mass =
+
© 2009 Brooks/Cole - Cengage
© 2009 Brooks/Cole - Cengage
Elements, Molecules,
Ions, Compounds
11
ELEMENTS THAT EXIST AS
DIATOMIC MOLECULES
PLAY MOVIE
NaCl, salt
Ethanol, C2H6O
Buckyball, C60
© 2009 Brooks/Cole - Cengage
© 2009 Brooks/Cole - Cengage
12
Chapter 2 — Atoms, Molecules, Ions
ELEMENTS THAT EXIST AS
POLYATOMIC MOLECULES
White P4 and polymeric
red phosphorus
S8 sulfur
molecules
4
13
ELEMENTS THAT EXIST AS
MOLECULES
Carbon Allotropes (different structural forms
with different chemical & physical properties)
O2 and O3
oxygen
molecules
© 2009 Brooks/Cole - Cengage
IONS AND IONIC COMPOUNDS
14
© 2009 Brooks/Cole - Cengage
15
Charges on Common Ions
-3 -2 -1
+1
+2
+3
By losing or gaining e-, atom has same number of
e- s as nearest Group 8A atom.
© 2009 Brooks/Cole - Cengage
© 2009 Brooks/Cole - Cengage
16
Chapter 2 — Atoms, Molecules, Ions
5
Predicting Charges on Monatomic Ions
17
18
METALS
M → n e- + Mn+
where n = periodic group
Na+
sodium ion
Mg2+
magnesium ion
Al3+
aluminum ion
Transition metals → M2+ or M3+ are common
Fe2+
iron(II) ion
Fe3+
iron(III) ion
Always the same charge: 1A, 2A, 3A, 5A, 6A, 7A, Ag+, Zn2+
© 2009 Brooks/Cole - Cengage
© 2009 Brooks/Cole - Cengage
19
NONMETALS
2 Al(s) + 3 Br2 (l) → Al2Br6(s)
NONMETAL + n e- → Xnwhere n = 8 - Group no.
Group 4A
Group 5A
Group 6A
Group 7A
C4-,carbide N3-, nitride O2-, oxide F-, fluoride
Name derived by
adding -ide to
stem
© 2009 Brooks/Cole - Cengage
20
Reaction of
aluminum
and
bromine
S2-, sulfide Cl-, chloride
Br-, bromide
PLAY MOVIE
I-,
iodide
© 2009 Brooks/Cole - Cengage
Chapter 2 — Atoms, Molecules, Ions
6
21
22
POLYATOMIC IONS
Groups of atoms with a
charge.
MEMORIZE the names and
formulas in Table 2.4, page
74.
Note: many O
containing anions
have names ending
in –ate (or -ite).
Celestite, SrSO4
© 2009 Brooks/Cole - Cengage
© 2009 Brooks/Cole - Cengage
23
Polyatomic Ions
NH4+
ammonium ion
One of the few common polyatomic
cations
© 2009 Brooks/Cole - Cengage
24
Polyatomic Ions
CO32carbonate ion
HCO3bicarbonate ion
hydrogen carbonate
© 2009 Brooks/Cole - Cengage
Chapter 2 — Atoms, Molecules, Ions
25
26
Naming Oxyanions
(they contain oxygen)
increasing
oxygen content
Polyatomic Ions
7
CH3CO2acetate ion
ClO4-
perchlorate
ClO3-
chlorate (most common oxyanion)
ClO2-
chlorite
ClO-
hypochlorite
All have the same overall charge and different number of O
atoms, so oxidation number of Cl is different in each
© 2009 Brooks/Cole - Cengage
Polyatomic Ions
© 2009 Brooks/Cole - Cengage
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28
Polyatomic Ions
NO3nitrate ion
SO42sulfate ion
NO2nitrite ion
SO32sulfite ion
© 2009 Brooks/Cole - Cengage
© 2009 Brooks/Cole - Cengage
Chapter 2 — Atoms, Molecules, Ions
IONIC COMPOUNDS
8
29
30
Electrostatic Forces
NH4+
PLAY MOVIE
Cl-
The oppositely charged ions in ionic compounds are
attracted to one another by ELECTROSTATIC FORCES.
These forces are governed by COULOMB S LAW.
ammonium chloride, NH4Cl
© 2009 Brooks/Cole - Cengage
© 2009 Brooks/Cole - Cengage
31
Ionic Compounds are Brittle
32
Electrostatic Forces
COULOMB S LAW
As ion charge increases, the attractive force _______________.
As the distance between ions increases, the attractive force
________________.
© 2009 Brooks/Cole - Cengage
© 2009 Brooks/Cole - Cengage
Chapter 2 — Atoms, Molecules, Ions
9
33
Electrostatic Forces
Importance of Coulomb s Law
COULOMB S LAW
NaCl,
m.p. 804oC
Na2O, Na+ and O2-,
m.p. 1132oC
© 2009 Brooks/Cole - Cengage
NaF,
m.p. 993oC
CaO, Ca2+ and O2m.p. 2572oC
(Na+ and Ca2+ are
similar size)
© 2009 Brooks/Cole - Cengage
35
Determining Formulas
In chemical analysis we determine the % by weight of
each element in a given amount of pure compound and
derive the EMPIRICAL or SIMPLEST formula.
36
A compound of B and H is 81.10% B. What is
its empirical formula?
•  B2H5
Knowing the empirical formula, you must do an
experiment to determine the MOLAR MASS in order
to find the MOLECULAR FORMULA.
© 2009 Brooks/Cole - Cengage
34
© 2009 Brooks/Cole - Cengage
Chapter 2 — Atoms, Molecules, Ions
10
37
A compound of B and H is 81.10% B. Its empirical
How to Determine a Formula?
formula is B2H5. What is its molecular formula?
We need to do an EXPERIMENT to find the MOLAR MASS.
Experiment gives molar mass = 53.3 g/mol
Compare with the mass of B2H5 = 26.66 g/unit
Find the ratio of these masses.
2 units of B2H5
53.3 g/mol
=
26.66 g/unit of B2H5
1 mol
Molecular formula = B4H10
© 2009 Brooks/Cole - Cengage
© 2009 Brooks/Cole - Cengage
39
Mass Spectrum of C2H6O:
is it CH3CH2OH or CH3OCH3?
CH3O+
C2H5O+
C2H5+
CH3+
© 2009 Brooks/Cole - Cengage
C2H6O+
38
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