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"If, in some cataclysm, all of scientific knowledge
were to be destroyed, and only one sentence passed on to the next
generations of creatures, what statement would contain the most
information in the fewest words? I believe it is the atomic hypothesis
(or the atomic fact, or whatever you wish to call it) that all
things are made of atoms---little particles that move around in
perpetual motion, attracting each other when they are a little
distance apart, but repelling upon being squeezed into one another''.
- Richard Feynman
THE ATOM
An atom is the smallest part of an element
with all the properties of that element. And an element
is the simplest type of pure substance. A single molecule
of water is not an element because it can be broken down into
the pure elements of oxygen and hydrogen. Oxygen and hydrogen
can not be broken down into simpler substances without the
great effort of a nuclear reaction. An atom is composed of
protons, neutrons and electrons. A proton contains
a positive charge and is approximately equal in mass
to a netron which has no charge. Since protons wish to
repel each other by their like electric charges, they
are held together by the neutrons in the center (or nucleus)
of the atom. Electrons are negatively charged and are
attracted to the protons staying in orbit around the nucleus.
It takes approximately 2000 electrons to weigh as much as
one proton or neutron!
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THE PERIODIC TABLE (of the Elements)
The Periodic Table of Elements (shown below) lists over 100 of the
available elements (92 naturally occuring) we have at our disposal
for constructing the more complex molecules and compounds. Atoms
are arranged in the Periodic Table according to their atomic number.
The atomic number (Z) of an element determines the number
of protons an atom of that element contains. For every proton
in an atom there is also an equal number of electrons.
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+1 |
+2 |
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+3 |
±4 |
-3 |
-2 |
-1 |
0 |
| 1 |
1
H |
|
2
He |
| 2 |
3
Li |
4
Be |
|
5
B |
6
C |
7
N |
8
O |
9
F |
10
Ne |
| 3 |
11
Na |
12
Mg |
|
13
Al |
14
Si |
15
P |
16
S |
17
Cl |
18
Ar |
| 4 |
19
K |
20
Ca |
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21
Sc |
22
Ti |
23
V |
24
Cr |
25
Mn |
26
Fe |
27
Co |
28
Ni |
29
Cu |
30
Zn |
31
Ga |
32
Ge |
33
As |
34
Se |
35
Br |
36
Kr |
| 5 |
37
Rb |
38
Sr |
|
39
Y |
40
Zr |
41
Nb |
42
Mo |
43
Tc |
44
Ru |
45
Rh |
46
Pd |
47
Ag |
48
Cd |
49
In |
50
Sn |
51
Sb |
52
Te |
53
I |
54
Xe |
| 6 |
55
Cs |
56
Ba |
* |
71
Lu |
72
Hf |
73
Ta |
74
W |
75
Re |
76
Os |
77
Ir |
78
Pt |
79
Au |
80
Hg |
81
Tl |
82
Pb |
83
Bi |
84
Po |
85
At |
86
Rn |
| 7 |
87
Fr |
88
Ra |
** |
103
Lr |
104
Rf |
105
Db |
106
Sg |
107
Bh |
108
Hs |
109
Mt |
110
Uun |
111
Uuu |
112
Uub |
113
Uut |
114
Uuq |
115
Uup |
116
Uuh |
117
Uus |
118
Uuo |
| |
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| *Lanth |
* |
57
La |
58
Ce |
59
Pr |
60
Nd |
61
Pm |
62
Sm |
63
Eu |
64
Gd |
65
Tb |
66
Dy |
67
Ho |
68
Er |
69
Tm |
70
Yb |
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| **Act |
** |
89
Ac |
90
Th |
91
Pa |
92
U |
93
Np |
94
Pu |
95
Am |
96
Cm |
97
Bk |
98
Cf |
99
Es |
100
Fm |
101
Md |
102
No |
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Click here for a more
extensive Periodic Table.
ELECTRON BEHAVIOR
1) Electrons and protons are attracted to each other, even
if they are in different atoms.
2) Electrons also arrange themselves around the nucleus in specific
patterns.
It is these 2 characteristics that determine how atoms bond to each
other to form molecules. There are only 2 elements in the
first row in the periodic table because only 2 electrons can occupy
the first energy shell. The 2nd shell can hold 8, the 3rd - 18,
the 4th - 32, the 5th - 50, etc. The equation e = 2n2
determines the maximum allowable electrons that can fit in a shell
(n=shell number). Another oddity is that the outer (valence)
shell is quite particular, only tolerating a maximum of 8
electrons (except for Hydrogen and Helium which can only hold
2). This is called the octet rule. As we move down the table
adding protons, electrons and neutrons, the outer shell gets its
full 8 and the next shell begins to fill. Since the 3rd shell can
actually hold more than 8, when we get to the 4th shell, we add
a couple electrons ( K and Ca ) and then start adding again to the
3rd shell until it packs out its capacity of 18, and then the 4th
begins filling again (Ga) until it reaches its full 8 at Krypton.
Because atoms like to have a full outer shell, they will
bond with other atoms in an attempt to satisfy this "urge".
Elements on the left of the table tend to have fewer outer shell
electrons and will give up electrons (-) and become more positive
(+). The remaining subshell which is full now becomes the outer
shell. Elements on the right of the table tend to have a fuller
outer shell and would rather gain electrons (-) and become more
negative. Elements in the 1st column of the table (+1) all
have 1 electron in the outer shell, the 2nd column (+2) have
2.. The 6 columns on the right have 3, 4, 5, 6, 7 and 8 electrons
in the outer shell, having charges of + 3, ±4, -3, -2, -1,
and 0 respectively. The column with the 0 will actually neither
gain or lose because of a filled outer shell. These are called Nobel
gases and form no naturally occuring compounds. The ±4 column
all have 4 electrons in the outer shell and could go either way
in losing or gaining electrons to form a compound.
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