Download mass of an atom - CHM101-02

Chapter 3
III. Atomic Structure
A. Components of atoms
+
a) electron, e- (negatively charged), -1.6 x 10-19 C
mass = 1/1838 that of a H atom
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b) proton, p+ (positively charged)
mass  mass of H atom
2
c) Neutron, n (no charged)
mass  mass of H atom
Charge and Mass Characteristics of
Electrons, Protons, and Neutrons.
unit charge
electron, e- (negatively charged), -1.6 x 10-19 C
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d) Symbols of elements
atomic number, Z = number of protons in an atom of a
given element
mass number, A = # of protons + # of neutrons
= (# of nucleons)
A
ZX
Examples
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B. Isotopes
Not all atoms of the same element have the same mass
Example: There are 3 kinds of Hydrogen atoms
H
D
T
hydrogen-1
hydrogen-2
hydrogen-3
(protium)
(deuterium)
(Tritium)
mass ratio
Symbol
1
1
1H
1 e-, 1 p+
2
3
2
1H
3
1H
1 e-, 1 p+,1 n
Isotopes: Atoms with the same # of p+s and e-s but different # of n's.
They have the same chemical properties except that
they are different in mass
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Isotopes are atoms of the same element with different number
of neutrons.
Examples
12
6
C
14
6
C
All atoms of an element have the same atomic #
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C. Atomic mass (weight) – mass of an atom
Atomic mass unit (amu)
Mass of a H atom = 1.677 x 10-24 g
1
1
H
1 amu
4
2
He
4 amu
7
3
Li
12
6
C
(3p+s,4 ns)
(6 p+s, 6 ns)
1 amu = 1.667 x 10-24 g
In the periodic table, not all atomic masses (atomic weights) are
close to a whole number because of the existence of isotopes.
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Figure 3.3 The periodic table of the elements
period
Group
8
Example: Cl
35Cl
75%
37Cl
25%
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10
Halogens
Noble gases
Alkali metals
Alkaline earth metals
(Main group elements)
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Selected Physical Properties of
Metals and Nonmetals.
Metals
• are solids at room temperature (except for Hg, which is
a liquid), shiny, conduct electricity, and are ductile and
malleable.
• form alloys (solutions of one metal dissolved in another);
brass, for example, is an alloy of copper and zinc
• In chemical reactions, they tend to give up electrons.
Nonmetals
• Except for hydrogen (H), they lie on the right side of the
Periodic Table.
• Except for graphite, do not conduct electricity.
• In chemical reactions, they tend to accept electrons.
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Metalloids
• They have some of the properties of metals and some
of nonmetals; for example, they are shiny like metals
but do not conduct electricity.
• Six elements are classified as metalloids: boron,
silicon, germanium, arsenic, antimony, and tellurium.
• One of the metalloids, silicon, is a semiconductor; it
does not conduct electricity under certain applied
voltages, but becomes a conductor at higher applied
voltages.
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Tc
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D. The inner structure of the atom
Rutherford’s experiment
He2+
Observations
1. Most of them (a particles) went right through
2. A few deflected
3. Some bounced back from the gold foil
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http://video.google.com/videoplay?docid=1909836802101196671&q=rutherford+experiment&total=8&start=0&num=10&so
=0&type=search&plindex=0
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IV. Electron configuration of atoms
A. Experimental facts (Flame test)
A pure substance absorbs only certain energies and
emit certain energies.
From quantum mechanical calculations, electrons can
be in discrete energy levels only
Bohr
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IV. Electron configuration of atoms
A. Experimental facts
A pure substance absorbs only certain energies and
emit certain energies.
From quantum mechanical calculations, electrons can
be in discrete energy levels only
Bohr
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B. Energy levels
18
2
32
8
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a) Shells and
subshells
Energy levels
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b) Orbitals
Further studies indicate that electrons do not travel in circles
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Standing wave
23
p orbitals
z
24
d orbitals
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Figure
3.10
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c) Electron Spin
An electron in an orbital can either
spin up or spin down
spin up
1 A s pinnin g electron
generates a tiny
magn etic field
N
S
S
N
Spin down
electron pair
2 When their tin y magnetic
fields are align ed N -S, the
electron spin s are paired
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Electron Configuration and Orbital Diagrams
Orbital (box) diagram
Electron configuration
Pauli exclusive principle
3p
3s
2p
2s
He
1s 2
1s
H
1s 1
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Electron Configuration and Orbital Diagrams
Orbital diagram
Electron configuration
3p
3s
2p
2s
1s
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Orbital diagram
Electron configuration
3p
3s
2p
2s
1s
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Figure 3.11
The order of filling of
various electron
subshells is shown on
the right-hand side of
this diagram. Above
the 3p subshell,
subshells of different
shells "overlap".
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Copyright © Houghton Mifflin Company. All rights reserved.
3–13
Orbital (box) diagram
Electron configuration
4p
3d
4s
3p
3s
2p
2s
1s
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4p
3d
4s
3p
3s
2p
2s
1s
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Figure 3.12 The order
for filling electron
subshells with electrons
follows the order given by
the arrows in this diagram.
Start with the arrow at the
top of the diagram and
work toward the bottom of
the diagram, moving from
the bottom of one arrow to
the top o the next-lower
arrow.
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Copyright © Houghton Mifflin Company. All rights reserved.
3–14
Orbital diagram
Electron configuration
4p
3d
4s
3p
3s
2p
2s
1s
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Figure 3.13 Electron configurations and the
positions of elements in the periodic table.
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Figure 3.13 Electron configurations and the
positions of elements in the periodic table.
2s
2p
3p
3s
4s
3d
5s
6s
7s
4d
5d
6d
4p
5p
6p
4f
5f
37
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Figure 3.13 Electron configurations and the
positions of elements in the periodic table.
Os 1s22s22p6……………
2s
5d6
2p
3p
3s
4s
3d
5s
6s
7s
4d
5d
6d
4p
5p
6p
4f
5f
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