1
CHAPTER 2
• Read Chapter 2.
• Study all examples and complete all
exercises.
Chapter 2 Outline
•
•
•
•
Discovery of the three atomic particles
Isotopes
Periodic Table
Groups and Periods
2
ATOMS AND ELEMENTS
3
4
Origins of the Atomic Theory
• John Dalton-1803
• Law of Conservation of Matter
• Law of Definite Proportions
Water is always H2O not HO
• Law of Multiple Proportions
SO2 and SO3
5
Dalton’s Atomic Theory
1. All matter is composed of atoms.
2. Atoms of an element are alike, atoms
of different elements are different.
3. Atoms cannot be created, destroyed,
subdivided, or converted into atoms of
another element.
4. A compound is formed when different
atoms combine in fixed, simple, wholenumber ratio.
5. A chemical change is a rearrangement
of atoms.
6
Radioactivity
• One of the pieces of evidence for the
fact that atoms are made of smaller
particles came from the work of
•
Marie Curie (1876-1934).
She discovered radioactivity, the
spontaneous disintegration of some
elements into smaller pieces.
Alpha, a, mass 4 amu, charge +2
Beta, b, mass 1/1500 amu, charge -1
Gamma, g, no mass, no charge
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ATOMIC COMPOSITION
• Protons ( p, p+)
– + electrical charge
– mass = 1.672623 x 10-24 g
– relative mass = 1.007 atomic
mass units (amu)
• Electrons ( e, e-)
–
negative electrical charge
– relative mass = 0.0005 amu
• Neutrons ( n, n0)
no electrical charge
– mass = 1.009 amu
–
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ATOM
COMPOSITION
•Protons and neutrons are
in the nucleus.
•The number of electrons
is equal to the number of protons.
•Electrons in space around the nucleus.
•Atoms are extremely small.
•One teaspoon of water has 3 times
as many atoms as the Atlantic
Ocean has teaspoons of water.
The atom is mostly
empty space.
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Deflection of a Cathode Ray
10
Thomson’s Charge-to-Mass
Experiment
Millikan’s Oil Drop
Experiment
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12
The modern view of the atom was
developed by Ernest Rutherford
(1871-1937).
The Rutherford
Experiment
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How Large is an Atom?
Circle consists of
48 iron atoms.
Radius of circle is
71 Angstrom
units where
1 A = 1 x 10-8 cm.
STM image of “quantum corral” of iron
atoms
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Atomic Number, Z
All atoms of the same element
have the same number of
protons in the nucleus, Z
13
Al
26.9815
atomic number (Z)
symbol
atomic weight
16
Mass Number, A
C atom with 6 protons and 6 neutrons is the
mass standard
= 12 atomic mass units, amu
Mass Number = # protons + # neutrons
A Boron atom can have
A = 5 p + 5 n = 10
A
Z
10
5
B
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Isotopes
• Atoms of the same element (same Z)
but different mass number (A).
• Boron-10 (10B) has 5 p and 5 n
• Boron-11 (11B) has 5 p and 6 n
11B
10B
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Check Problems
Determine the mass number of a
mercury atom with 122 neutrons and
give its complete atomic symbol.
202
Hg
80
Determine the number of protons,
neutrons, and electrons in a Fe-55 atom.
26 p+, 26 e-, 29 n
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Mass Spectrometer
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Isotopes
11B
10B
• Because of the existence of isotopes, the
mass of a collection of atoms has an average
value.
• Average mass = ATOMIC WEIGHT
• Boron is 19.91% 10B and 80.09% 11B. That is,
11B is 80.09 percent abundant on earth.
• For boron atomic weight (mass)
= 0.1991 (10.01 amu) + 0.8009 (11.01 amu) =
10.811 amu
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Solution
1)
6Li
7Li
abundance
7.42%
92.58%
atomic mass
6.015 amu
7.016 amu
What is the atomic weight of Li?
(.0742)(6.015 amu) + (.9258)(7.016 amu)
.446313 amu + 6.4954… amu
6.941 amu
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Practice Problem
• Calculate the % abundance for the
two isotopes of gallium, given Ga
atomic weight is 69.723 amu, and:
Ga-69, 68.926 amu;
Ga-71, 70.925 amu
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Solution
2) Calculate the % abundance for the two
isotopes of gallium.
Ga-69, 68.926 amu; 60.13 %
Ga-71, 70.925 amu 39.87 %
x(68.926 amu) + (1-x)(70.925 amu) = 69.723 amu
68.926 x amu
69.723 amu
-70.925 x amu
-70.925 amu
-1.999 x amu
=
-1.202 amu
x = .6013
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Periodic Table
Lothar
Meyer
1869
(1830 – 1895)
The periodic
table arranges
elements
according to
similar
properties
Dimitri Mendeleev 1868 (1834 - 1907)
Mendeleev’s 1872 Periodic
Table
25
26
Periods in the Periodic Table
1-7
27
Groups in the Periodic Table
1-18
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Group 1: Alkali Metals
Reaction of
potassium and water
K + H2O
Cutting sodium metal
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Group 2: Alkaline Earth Metals
Magnesium
Magnesium
oxide
30
Group 13: B, Al, Ga, In, Tl
Aluminum
Boron halides,
BF3 & BI3
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Group 14: C, Si, Ge, Sn, Pb
Quartz, SiO2
Diamond
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from http://cnst.rice.edu/images
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Allotropes of Carbon
Graphite
Diamond
Buckyballs
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Group 15: N, P, As, Sb, Bi
Ammonia, NH3
White and red
Phosphorus
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Group 16: O, S, Se, Te, Po
Shuttle main engines
use H2 and O2
Sulfur
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Group 17: F, Cl, Br, I, At
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Group 18:
He, Ne, Ar, Kr, Xe, Rn
• Lighter than air
balloons
• “Neon” signs
XeOF4
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Transition Elements
Transition
elements
Inner transition elements
lanthanides and actinides
Iron in air gives
iron(III) oxide
Practice Problems
• The formula for aluminum sulfide
is Al2S3. What is the formula for
gallium sulfide?
Ga2S3
• What is the symbol and name of
the element in period three and
group fifteen?
P
phosphorus
• What is the group and period for
iodine?
Period 5 and Group 17
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Summary of the Periodic
Table Features
1. Name, Symbol, Atomic Number,
Atomic Mass.
2. Solid, liquid, gas
Summary of the Periodic
Table Features
3. Divisions:
metals
vs.
nonmetals
groups(families)
vs. periods(series)
1 alkali metals
transition metals
2 alkaline earth metals inner transition metal
(rare earth series)
17 halogens
18 noble gases
(inert or rare gas)
Main Group Elements (Representative Elements)
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Practice Problems
1. Draw atoms of O-16 and O-17.
Determine A and Z for each.
2. An atom has 14 p+, 14 e-, and 17 n.
Identify the element and write the
complete symbol for this atom.
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Practice Problems Answers
1. O-16 Z = 8, A = 16
O-17 Z = 8, A = 17
Protons and neutrons in the nucleus.
Electrons outside the nucleus.
2. 31
Si
14
3. a) In, Sr, Na, Ni
b) P, At, S, Ar
c) Ar d) Na e) At f) Ni g) none
h) In, Sr, P, At, S, Na, Ar
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Practice Problems
4. Calculate the atomic weight of Mg
from the following information:
mass
% abundance
Mg-24
23.9850 amu
78.99%
Mg-25
24.9858 amu
10.00%
Mg-26
25.9825 amu
11.01%
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Practice Problems
5. Thallium metal, whose atomic mass is
204.384 amu, consists of two isotopes, Tl203 and Tl-205. The isotopic mass of Tl203 is 202.972 amu. and the isotopic mass
of Tl-205 is 204.975 amu.
a) Determine the number of protons,
neutrons, and electrons in each isotope.
b) What is the % abundance of each
isotope?
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Practice Problems Answers
4. 24.31 amu
5. a) Tl-203 81 p, 81 e, 122 n
Tl-205 81 p, 81 e, 124 n
b) Tl-203 29.5%
Tl-205 70.5%