Download Mass Number, A Isotopes

Chapter 2 — Atoms, Molecules, Ions
ATOMIC COMPOSITION
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•  Protons
– 
– 
– 
The atom is mostly
empty space
+ electrical charge
mass = 1.672623 x 10-24 g
relative mass = 1.007 atomic
mass units (u or amu)
•  protons and neutrons in
the nucleus.
•  Electrons
– 
– 
•  electrons in space around the nucleus.
no electrical charge
mass = 1.009 u
•  extremely small. One teaspoon of water
has 3 times as many atoms as the Atlantic
Ocean has teaspoons of water.
•  1 u = ? g
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© 2009 Brooks/Cole - Cengage
Mass Number, A
•  C atom with 6 protons and 6 neutrons
is the mass standard
•  = 12 atomic mass units (u)
•  Mass Number (A)
= # protons + # neutrons
•  A boron atom can have
A = 5 p + 5 n = 10 u
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PLAY MOVIE
•  the number of electrons is equal to the
number of protons.
negative electrical charge
relative mass = 0.0005 u
•  Neutrons
– 
– 
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ATOM
COMPOSITION
A
10
Z
5
Isotopes
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•  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
11B
10B
B
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Chapter 2 — Atoms, Molecules, Ions
Hydrogen Isotopes
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Mass Spectrometer separates isotopes
Hydrogen has 3 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
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© 2009 Brooks/Cole - Cengage
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
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% 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
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Chapter 2 — Atoms, Molecules, Ions
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Isotopes
11B
Isotopes & Atomic Weight
•  Except for carbon-12 with mass = 12 u, isotopic masses are
not integer values. However they are very close to integers
10B
•  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 =
+
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© 2009 Brooks/Cole - Cengage
Elements, Molecules,
Ions, Compounds
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ELEMENTS THAT EXIST AS
DIATOMIC MOLECULES
PLAY MOVIE
NaCl, salt
Ethanol, C2H6O
Buckyball, C60
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© 2009 Brooks/Cole - Cengage
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Chapter 2 — Atoms, Molecules, Ions
ELEMENTS THAT EXIST AS
POLYATOMIC MOLECULES
White P4 and polymeric
red phosphorus
S8 sulfur
molecules
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O2 and O3
oxygen
molecules
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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.
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Carbon Allotropes (different structural forms
with different chemical & physical properties)
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IONS AND IONIC COMPOUNDS
ELEMENTS THAT EXIST AS
MOLECULES
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Chapter 2 — Atoms, Molecules, Ions
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Predicting Charges on Monatomic Ions
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METALS
M ➔ Mn+ + n ewhere 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+
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© 2009 Brooks/Cole - Cengage
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NONMETALS
NONMETAL + n e– ➔ Xnwhere n = 8 – Group #
Group 4A
Group 5A
Group 6A
Group 7A
C4-,carbide N3-, nitride O2-, oxide F-, fluoride
Name derived by
adding -ide to stem
Ion Formation
Reaction of
aluminum
and
bromine
S2-, sulfide Cl-, chloride
PLAY MOVIE
Br-, bromide
I-, iodide
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© 2009 Brooks/Cole - Cengage
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Chapter 2 — Atoms, Molecules, Ions
POLYATOMIC IONS
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Groups of atoms
with a single charge.
MEMORIZE the names
and formulas in
Table 2.4, page 74.
Celestite, SrSO4
Note: many O
containing anions
have names ending
in –ate (or -ite).
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© 2009 Brooks/Cole - Cengage
Polyatomic Ions
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Polyatomic Ions
NH4+
ammonium ion
One of the few common
polyatomic cations
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HNO3
nitric acid
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NO3nitrate ion
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Chapter 2 — Atoms, Molecules, Ions
Polyatomic Ions
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CO32carbonate ion
Polyatomic Ions
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CH3CO2acetate ion
HCO3bicarbonate ion
hydrogen carbonate
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© 2009 Brooks/Cole - Cengage
Naming Oxyanions
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Polyatomic Ions
increasing
oxygen content
(they contain oxygen)
ClO4-
perchlorate
ClO3-
chlorate (most common oxyanion)
ClO2
chlorite
ClO-
-
SO42sulfate ion
hypochlorite
SO32sulfite ion
All have the same overall charge and different number of
O atoms, so oxidation number of Cl is different in each
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© 2009 Brooks/Cole - Cengage
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Chapter 2 — Atoms, Molecules, Ions
Polyatomic Ions
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IONIC COMPOUNDS
NH4+
NO3nitrate ion
Cl-
NO2nitrite ion
ammonium
chloride,
NH4Cl
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© 2009 Brooks/Cole - Cengage
Electrostatic Forces
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Electrostatic Forces
COULOMB’S LAW
PLAY MOVIE
The oppositely charged ions in ionic compounds are
attracted to one another by ELECTROSTATIC FORCES.
These forces are governed by COULOMB’S LAW.
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As ion charge increases, the attractive force _______________.
As the distance between ions increases, the attractive force
________________.
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Chapter 2 — Atoms, Molecules, Ions
Electrostatic Forces
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Importance of Coulomb’s Law
COULOMB’S LAW
NaCl,
m.p. 804oC
Na2O, Na+ and O2-,
m.p. 1132oC
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NaF,
m.p. 993oC
CaO, Ca2+ and O2m.p. 2572oC
(Na+ and Ca2+ are
similar size)
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Naming Molecular
Compounds
Counting Atoms
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Chemistry is a quantitative
science—we need a
“counting unit.”
MOLE
CO2 Carbon dioxide
All are formed from
two or more
nonmetals.
1 mole is the amount of substance that
contains as many particles (atoms,
molecules) as there are in 12.0 g of 12C.
518 g of Pb, 2.50 mol
CH4 methane
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BCl3
boron trichloride
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Chapter 2 — Atoms, Molecules, Ions
Molar Mass
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Note that the mass of water is
included in the molar mass of a
compound.
Empirical & Molecular
Formulas
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A pure compound always consists of the same
elements combined in the same proportions
by weight.
Therefore, we can express molecular
composition as PERCENT BY WEIGHT
Ethanol, C2H6O
52.13% C
13.15% H 34.72% O
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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.
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A compound of B and H is 81.10% B. What is
its empirical formula?
•  81.1% B => 81.1 g B, 18.9% H => 18.9 g H
•  81.1 g B x 1 mol/10.81 g = 7.50 mol B
•  18.9 g H x 1 mol/1.00 g = 18.9 mol H
•  18.9 mol/7.50 mol = 2.52
•  Ratio (2.5 H : 1 B) x 2
•  B2H5
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© 2009 Brooks/Cole - Cengage
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Chapter 2 — Atoms, Molecules, Ions
A compound of B and H is 81.10% B. Its empirical
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formula is B2H5. What is its molecular formula?
How to Determine a 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
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© 2009 Brooks/Cole - Cengage
Mass Spectrum of C2H6O:
is it CH3CH2OH or CH3OCH3?
CH3O+
C2H5O+
C2H5+
CH3+
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C2H6O+
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