Chemistry and Physical Chemistry

Covalent:

  One or more electrons are shared between (atomic) nuclei. The difference between a covalent and an ionic bond is largely one of semantics.  If one or more electrons are mostly shared between two nuclei a bond is considered 'covalent' or has 'covalent character'.  If electrons are hardly shared (the electron is in the vicinity of one nucleus much, much more than it is in the vicinity of the other), the bond is considered ionic or has 'ionic character'.  While an ionic bond can be largely explained in terms of electric force, a covalent bond is largely the result of quantum phenomena that determine the structure of any given element's electron shells.  (Contrast with "ionic")
 
 

Fluorine:

Pale yellow gaseous element.  Atomic number 9.  It is highly reactive, combining spontaneously and violently with virtually all elements.  Fluorine disolves glass1.  It has a low cosmic abundance, significantly lower than that of oxygen.
 
 

Halogens:

The elements of group VII (fluorine, chlorine, bromine, iodine and astatine).  These elements all have seven valence electrons and most often react by either accepting an extra electron from a metal to form an halide ion or by forming a single covalent bond with a nonmetal.  All of them except fluorine can also donate electrons to more electronegative elements forming such compounds as Cl2O7.
 
 

Ion:

A charged particle.   For example, if you dissolve common salt (sodium chloride) in water, it dissociates into ions, Na+  (loosing an electron) and Cl- (gaining an electron).  Note that the solution as a whole has no net charge, and is not referred to as "ionized".  "Ion" is a fundamental concept in chemistry and related fields.

Molecules formed with this type of bond (that dissociate into ions when dissolved in a solvent) are said to be "ionic" molecules, and the molecular bond is called "ionic" because the atoms actually exchange one or more electrons rather than mutually sharing electrons.  In an ionic bond, electrons are shared so poorly that the negative ion can separate from its positive ion completely, taking the electron(s) with it.  This happens commonly in solution.  Without a solvent, the atoms remain in molecular proximity due to electrical force.  (Contrast with "covalent" bonds and molecules, where electrons are not passed from one atom to another.)
 
 

Ionized:

(The past participle of the verb to ionize:) A molecule, or molecules, that have become ionic.  A substance consisting entirely of ions.  A substance with a substantial number of molecules that are ions, and hence has a net electrical charge.  For example, an "ionized gas" is one that has had enough energy pumped into it so that most of the constituent atoms are ions.
 
 

Oxygen:

Oxygen is the third most common element in the universe.  Its most common isotope is O16. It is the second most electronegative element and highly reactive.  Oxygen forms about half the mass of typical terrestrial planets, mostly in the form of silicates.  Molecular oxygen has two allotropes, the metastable ozone and O2.  Ozone is formed by the action of ultraviolet light in the upper regions of nitrogen/ oxygen atmospheres through a complex series of free radical reactions, and significantly reduces the ultraviolet flux at the surface of the planets, with consequent beneficial consequences for the life on them.  Oxygen is an important part of all biochemistry, and drives the process of respiration.

O2:

The normal form of molecular oxygen is O2, a colorless paramagnetic gas.  It has an unusual electronic structure, which is responsible for both its unusual magnetic properties, and the slow rates of its reactions.  Every element, except Fluorine and the noble gases, combines spontaneously with oxygen at galactic standard temperature and pressure, as do almost all compounds. However, in most cases this reaction is very slow by chemical standards.  Iron rusts, and all organic compounds oxidize, but slowly over periods ranging from days to decades.  This is because molecular oxygen is a stable diradical.   It has two electrons in an unpaired triplet state.  Oxygen is the only naturally occurring chemical with this property.  Free radicals are rare, and mostly highly reactive.  Diradicals of any kind are very rare, but stable diradicals are extremely unusual.  This makes reactions in which an electron pair is donated to oxygen unfavorable, because the spin of one electron must be inverted.  The excited singlet form of oxygen, that does not have this barrier, reacts swiftly with almost all compounds.  Oxidation instead normally occurs through free radical procedures, and hence is slowed by the difficulty of the initial step.  Were it not for this fortuitous and unusual property of of O2's molecular structure, organic life would not be viable in the presence of oxygen.

(by Robert Shaw)
 
 

Periodic table:

A table in which the elements are arranged by increasing atomic number, from left to right and top to bottom, and in columns  based on recurring  patterns of chemical behavior (the major columns are traditionally known as groups 0 and I-VII)


The Periodic Table of Elements2
Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Period
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
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
-
*Lanthanoids * 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
**Actinoids ** 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

Notes: elements 113 and 115-118 are not known, but are included in the table to show their expected positions. There are unconfirmed reports for the observation of element 114 and so this element (ununquadium, Uuq) is also included.


In general elements represented to the left of the chart are metallic.  Metallic behavior also predominates at higher atomic numbers.  Elements with higher numbers are represented at lower levels on the chart.  Some of the groups are named; for example elements in group VII are halogens (see column 17) and group 0 are the noble gases (see column 18).  The transition elements (shown between groups II and III--that is, columns 3 to 12, above) have similar properties to each other, varying much less in their chemical behaviors than the elements in the main groups. Within this block, iron, nickel and cobalt are especially similar as are the analogous elements in rows to the right.  The transition elements of copper, silver and gold are collectively known as the noble metals, each being relatively inert and conductive.  In the 6th and subsequent rows the rare earths are inserted into the transition block. These form two series, the Lanthanides (in the 6th row) and the Actinides (in the 7th row). The elements of each series are all but indistinguishable by standard chemical means.

Electrons fill the space around an atom according to certain physical rules.  The space around an atom can be thought of as a series of "shells."  Only a fixed number of electrons can coexist in a given shell. The rules for filling electron shells mean that different elements will have similar chemical properties.  Furthermore, the recurrence of these properties is predictable based on an element's atomic number.  In short, the chemical properties of elements reoccur "periodically."  Hence the name of the table.

In groups 0-VII the outermost shell (generally) contains 0-7 electrons, corresponding to the group number.  (Or in the case of group 0, we can say that the outer shell is full.)  In the transition elements, the additional electrons are being added to the next to last shell instead of the outermost, making the chemical properties of these elements rather similar.  In the rare earth elements the additional electrons are added to the next to the next to the last shell (that is two shells in from the outermost shell)  making the chemical properties of the rare earth elements nearly identical.

On Earth, the periodic table was first discovered by the Russian chemist Dmetri Mendeleyev in 1869.  With its aid, he predicted the properties of some elements that had yet to be discovered.  All elements after polonium have no stable isotopes, those after plutonium (inclusive) do not occur naturally.  Humans synthesized elements 95-116 in the pre-collapse period.
 
 

Plasma:

an extremely energetic "gas" that consists of atomic nuclei stripped of electrons.  That is, a plasma is composed of positive ions and "free" electrons.  Plasma behaves differently enough from gases that plasmas are referred to as "the fourth state of matter."

Plasmas are produced in extreme conditions of very high temperatures or by applying high voltage across metal plates enclosing a gas. For industrial and laboratory use, the gas is often significantly below atmospheric pressure and enclosed in a quartz tube.  Also, a lot of the processing equipment for semiconductor circuit manufacturing produces a plasma used to engineer the semiconductor material itself.  In this industrial application a microwave frequency electric field is usually used to produce the plasma.  In a star, most matter is plasma.
 


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S.V. van Baardwijk-Holten says:

Fluorine is not all that bad. But it  has another neat feature.  It disolves glass.  So if you've got a glass mirror that has a scratch put some fluorine touthpaste on, rub with a dry towl and leave it for a night to dry and then remove with water.  No more scratch.
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WebElements2000, the periodic table on the WWW, URL: http://www.webelements.com/

Document URL: http://www.shef.ac.uk/chemistry/web-elements/webelements/elements/text/key/pe riodic-table.html
Copyright 1993-1999 Mark Winter [University of Sheffield, England]
Document modification date: 6 May 1999

Reproduced with permission of M. Winter

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Contributors:  Charlie Bell, Keith Douglas, Terry D. Johnson, Alberto Montiero, Robert Shaw, Eileen Tan.


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