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Atoms
T. M. Yeung 2000

What is the particle that made up an
element?
Atoms

All elements are made
up of small particles
called atoms.
 Different elements
have their unique kind
of atoms.
 The atoms of iron are
different from that of
carbon.
Gold and its Atoms
Different Elements are made up
of different atoms
a silver
wire
silver atoms
enlarged many,
many times
a copper
wire
copper atoms
enlarged many,
many times
Basic Structure of Atom
electron
neutron
proton
Solar System
Basic Structure of Atom
Particle
Symbol
p
Relative
Mass
1
Relative
Charge
+1
Proton
(質子)
Electron
(電子)
Neutron
(中子)
e-
1/18400
-1
n
1
0
Atomic Number & Mass Number
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An Atom is electrically neutral, that means
No. of proton(s) in an atom
= No. of electron(s) in the same atom
Atomic Number (Z) of an atom
= No. of proton(s) of the atom
Mass Number (A) of an atom
= No. of proton(s) + No. of neutron(s)
Example

What is the atomic number and the mass number
of the atom shown below? Atomic number is 2
and mass number is 4
neutron
electron
proton
nucleus
Class-work
Atom Symbol Atomic Mass No. of No. of No. of
no. (Z) no. (A) proton neutron electron
Hydro H
gen
1
1
1
0
1
Beryll Be
ium
4
9
4
5
4
Sodiu Na
m
11
23
11
12
11
Notation of Atom

X = symbol of element
 Z = atomic number
 A = mass number
A
Z
X
Notation of Atom
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
Atomic no. =?
92
Mass no. =?
235
No. of the neutron =?
143
Name =?
Uranium
235
92
U
Atomic Bombing at Nagasaki
Class-work
Atom
35
17 Cl
27
13 Al
40
20 Ca
31
15 P
No. of No. of No. of
proton neutron electron
17
18
17
13
14
13
20
20
20
15
16
15
Isotopes of Hydrogen
Isotopes of Hydrogen
Name
Symbol
Hydrogen-1
1
1
Hydrogen-2
2
1
Hydrogen-3
3
1
Atomic
no.
1
Mass no.
H
1
2
H
1
3
H
1
Chemistry Dictation


First 20 elements
10 minutes:
Relative Atomic Mass
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The mass of a hydrogen atom is only
1.66 x 10-24g!
The mass of a carbon atom is only
2 x 10-23g!
(0.00 000 000 000 000 000 000 002g!)
Carbon-12 atom is being taken as the
reference standard.
The relative atomic mass of carbon-12
atom is defined as 12 units.
Relative Atomic Mass
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
Most elements have more than one isotope,
and different isotopes have different masses.
The relative atomic mass of an element is
the average mass of its isotopes compare
with an atom carbon-12.
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Isotope
Percentage abundance
35Cl
75%
37Cl
25%
Relative atomic mass of chlorine, Cl:
75/100 x 35 + 25/100 x 37
= 35.5 (a.m.u.) #
Relative atomic mass of lead, Pb:
2/100 x 204 + 24/100 x 206 + 22/100 x 207
+ 52/100 x 208
= 207.2 (a.m.u.) #
Electron Arrangement of Atoms
Shell
Number (n)
1
Maximum
Number
of
Electrons (2n2)
2
2
8
3
18
nucleus
Electron Arrangement of Atoms

Oxygen atom
 Atomic no. = 8
 No. of protons
= No. of electrons
=8
 Electron arrangement
= 2, 6
O
Electron
Electron Arrangement of Atoms

Oxygen atom
 Atomic no. = 8
 No. of protons
= No. of electrons
=8
 Electron arrangement
= 2, 6
O
Electron
Electron Arrangement of Atoms

Oxygen atom
 Atomic no. = 8
 No. of protons
= No. of electrons
=8
 Electron arrangement
= 2, 6
O
Electron
Electron Arrangement of Atoms

Oxygen atom
 Atomic no. = 8
 No. of protons
= No. of electrons
=8
 Electron arrangement
= 2, 6
O
Electron
Electron Diagram of Oxygen
Atom

O
electron
Two electrons in the
first shell.
 Six electrons in the
second shell.
 Electron arrangement
= 2, 6
Electron Diagram of Aluminium
Atom
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Al
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Atomic no. = 13
Electron arrangement
=2, 8, 3
Two electrons in the
first shell.
Eight electrons in the
second shell.
Three electrons in the
third shell
Electron Diagram of Magnesium
Atom

Atomic no. = 12
 Electron arrangement
= 2, 8, 2
Mg
Electron Diagram of Fluorine
Atom

Atomic no. = 9
 Electron arrangement
= 2, 7
F
Electron Diagram of Boron Atom

Atomic no. = 5
 Electron arrangement
= 2, 3
B
Simple Ions

A simple ion is formed
when an atom either
loses or gains one or
more electrons.
 It is either positively
or negatively charged.
 Positive ions are called
cations.
Simple Ion
Simple Ion: Cation

Li
Lithium atom, Li:
 Atomic no. = 3
 Electron arrangement
= 2, 1
 Remove one electron
from the outermost
shell of lithium atom...
Simple Ion: Cation
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+
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Li
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Lithium ion, Li+:
Atomic no. = 3
Electron arrangement
=2
Three protons
Two electrons
Positively charged
particle!
Simple Ion: Anion
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F
Fluorine atom, F:
 Atomic no. = 9
 Electron arrangement
= 2, 7
 Add one electron to
the outermost shell of
fluorine atom...
Simple Ion: Anion
-  Fluoride ion, F :
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F
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Atomic no. = 9
Electron arrangement
= 2, 8
Nine protons
Ten electrons
Negatively charged
particle
References

Atomic Bomb
• http://www.geocities.com/Athens/Agora/4526/i
ndex1.html


Encarta 98
General Chemistry
• http://wwwwilson.ucsd.edu/education/gchem/index.html

General Chemistry I -- A Virtual Textbook
• http://wine1.sb.fsu.edu/chm1045/chm1045.htm