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what is the chemical elements?




A chemical element, or an element, is a material which cannot be broken down or changed into another substance using chemical means. Elements may be thought of as the basic chemical building blocks of matter. Depending on how much evidence you require to prove a new element has been created, there are 117 or 118 known elements.
external image b0019.gif



Name: Cobalt
Symbol: Co
Atomic Number: 27
Atomic Mass: 58.9332 amu
Melting Point: 1495.0 °C (1768.15 K, 2723.0 °F)
Boiling Point: 2870.0 °C (3143.15 K, 5198.0 °F)
Number of Protons/Electrons: 27
Number of Neutrons: 32
Classification: Transition Metal
Crystal Structure: Hexagonal
Density @ 293 K: 8.9 g/cm3
Color: silver



Isotope
Half Life
Co-56
77.3 days
Co-57
271.8 days
Co-58
70.9 days
Co-58m
9.1 hours
Co-59
Stable
Co-60
5.3 years
Co-60m
10.5 minutes
Co-61
1.7 hours


Date of Discovery: 1737
Discoverer: George Brandt
Name Origin: From the German word kobalt or kobold (evil spirit)
Uses: magnets, ceramics, special glasses
Obtained From: arsenic, oxygen, sulfur, cobaltine

taken from:http://www.chemicalelements.com/elements/co.html


[Periodic Table of the Elements]
[Periodic Table of the Elements]

external image 2c2ca640.jpg

chemical elements


A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. Common examples of elements are iron, copper, silver, gold, hydrogen, carbon, nitrogen, and oxygen. In total, 118 elements have been observed as of March 2010, of which 94 occur naturally on Earth. 80 elements have stable isotopes, namely all elements with atomic numbers 1 to 82, except elements 43 and 61 (technetium and promethium). Elements with atomic numbers 83 or higher (bismuth and above) are inherently unstable, and undergo radioactive decay. The elements from atomic number 83 to 94 have no stable nuclei, but are nevertheless found in nature, either surviving as remnants of the primordial stellar nucleosynthesis that produced the elements in the solar system, or else produced as short-lived daughter-isotopes through the natural decay of uranium and thorium
All chemical matter consists of these elements. New elements of higher atomic number are discovered from time to time, as products of artificial nuclear reactions.









[Periodic Table of the Elements]
[Periodic Table of the Elements]





Chemical elements

A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements are iron, copper, silver, gold, hydrogen, carbon, nitrogen, and oxygen. In total, 117 elements have been observed as of 2008, of which 94 occur naturally on Earth. 80 elements have stable isotopes, namely all elements with atomic numbers 1 to 82, except elements 43 and 61 (technetium and promethium). Elements with atomic numbers 83 or higher (bismuth and above) are inherently unstable, and undergo radioactive decay. The elements from atomic number 83 to 94 have no stable nuclei, but are nevertheless found in nature, either surviving as remnants of the primordial stellar nucleosynthesis that produced the elements in the solar system, or else produced as short-lived daughter-isotopes through the natural decay of uranium and thorium.
All chemical matter consists of these elements. New elements of higher atomic number are discovered from time to time, as products of artificial nuclear reactions.

taken of ////http://en.wikipedia.org/wiki/Chemical_element////


.


A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. Common examples of elements are iron, copper, silver, gold, hydrogen, carbon, nitrogen, and oxygen. In total, 118 elements have been observed as of March 2010, of which 94 occur naturally on Earth. 80 elements have stable isotopes, namely all elements with atomic numbers 1 to 82, except elements 43 and 61 (technetium and promethium). Elements with atomic numbers 83 or higher (bismuth and above) are inherently unstable, and undergo radioactive decay. The elements from atomic number 83 to 94 have no stable nuclei, but are nevertheless found in nature, either surviving as remnants of the primordial stellar nucleosynthesis that produced the elements in the solar system, or else produced as short-lived daughter-isotopes through the natural decay of uranium and thorium.wikipedia/chemical/elements.com


Atomic number

The atomic number of an element, Z, is equal to the number of protons that defines the element. For example, all carbon atoms contain 6 protons in their nucleus; so the atomic number "Z" of carbon is 6. Carbon atoms may have different numbers of neutrons, which are known as isotopes of the element.
The number of protons in the atomic nucleus also determines its electric charge, which in turn determines the electrons of the atom in its non-ionized state. This in turn (by means of the Pauli exclusion principle) determines the atom's various chemical properties. So all carbon atoms, for example, ultimately have identical chemical properties because they all have the same number of protons in their nucleus, and therefore have the same atomic number. It is for this reason that atomic number rather than mass number(or atomic weight) is considered the identifying characteristic of an element.


Atomic mass

The mass number of an element, A, is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes of a given element are distinguished by their mass numbers, which are conventionally written as a super-index on the left hand side of the atomic symbol (e.g., 238U).
The relative atomic mass of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance, relative to the atomic mass unit (u). This number may be a fraction that is not close to a whole number, due to the averaging process. On the other hand, the atomic mass of a pure isotope is quite close to its mass number. Whereas the mass number is a natural (or whole) number, the atomic mass of a single isotope is a real number that is close to a natural number. In general, it differs slightly from the mass number as the mass of the protons and neutrons is not exactly 1 u, the electrons also contribute slightly to the atomic mass, and because of the nuclear binding energy. For example, the mass of 19F is 18.9984032 u. The only exception to the atomic mass of an isotope not being a natural number is 12C, which has a mass of
exactly 12, due to the definition of u (it is fixed as 1/12th of the mass of a free carbon-12 atom, exactly).
external image 99e1d8b62206a47de2046c10f5e11f96_3D_Chemical_Elements_ScreenSaver.jpg

Isotopes

Main articles: Isotope and Stable isotope
Isotopes are atoms of the same element (that is, with the same number of protons in their atomic nucleus), but having different numbers of neutrons. Most (66 of 94) naturally occurring elements have more than one stable isotope. Thus, for example, there are three main isotopes of carbon. All carbon atoms have 6 protons in the nucleus, but they can have either 6, 7, or 8 neutrons. Since the mass numbers of these are 12, 13 and 14 respectively, the three isotopes of carbon are known as carbon-12, carbon-13, and carbon-14, often abbreviated to 12C, 13C, and 14C. Carbon in everyday life and in chemistry is a mixture of 12C, 13C, and 14C atoms.
Except in the case of the isotopes of hydrogen (which differ greatly from each other in relative mass—enough to cause chemical effects), the isotopes of the various elements are typically chemically nearly indistinguishable from each other. For example, the three naturally-occurring isotopes of carbon have essentially the same chemical properties, but different nuclear properties. In this example, carbon-12 and carbon-13 are stable atoms, but carbon-14 is unstable; it is radioactive, undergoing beta decay into nitrogen-14.
As illustrated by carbon, all of the elements have some isotopes that are radioactive (radioisotopes), which decay into other elements upon radiating an alpha or beta particle. Certain elements
only have radioactive isotopes: specifically the elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic numbers greater than 82.
Of the 80 elements with at least one stable isotope, 26 have only one stable isotope, and the mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for an element is 10 (for tin, element 50).

taken of //http://en.wikipedia.org/wiki/File:Periodic_table.svg//
what is a chemical element?
is a substance that cannot be divided or changed into different substances by ordinary chemical methods. The smallest particle of such an element is an atom, which consists of electrons centered around a nucleus of protons and neutrons.

Radioactive decay
is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the
parent nuclide transforming to an atom of a different type, named the daughter nuclide. For example: a carbon-14 atom (the "parent") emits radiation and transforms to a nitrogen-14 atom (the "daughter"). This is a stochastic process on the atomic level, in that it is impossible to predict when a given atom will decay,[1] but given a large number of similar atoms the decay rate, on average, is predictable.
The SI unit of activity is the becquerel (Bq). One Bq is defined as one transformation (or decay) per second. Since any reasonably-sized sample of radioactive material contains many atoms, a Bq is a tiny measure of activity; amounts on the order of GBq (gigabecquerel, 1 x 109 decays per second) or TBq (terabecquerel, 1 x 1012 decays per second) are commonly used. Another unit of radioactivity is the curie, Ci, which was originally defined as the amount of radium emanation (radon-222) in equilibrium with of one gram of pure radium, isotope Ra-226. At present it is equal, by definition, to the activity of any radionuclide decaying with a disintegration rate of 3.7 × 1010 Bq. The use of Ci is presently discouraged by the SI.
external image bis.fcgi?rt=GetFile&uri=!!TD435W9M42&type=0&index=2
taken from: http://en.wikipedia.org/wiki/Radioactive_decay






Chemical Elements Table

See the interactive periodic table.
Element
Sym-
bol
Atomic
no.
Atomic
wt.
Specific
gravity
Melting
point
°C
Boiling
point
°C
No. of
isotopes1
Discoverer
Year
Actinium
Ac
89
2272
10.073
1051
3198
11
Debierne/Giesel
1899/1902
Aluminum
Al
13
26.981538
2.6989
660.32
2519
8
Wöhler
1827
Americium
Am
95
2432
13.67
1176
2011
134
Seaborg et al.
1944
Antimony
Sb
51
121.76
6.61
630.63
1587
29
Early historic times

Argon
Ar
18
39.948
1.78375
-189.35
-185.85
8
Rayleigh and Ramsay
1894
Arsenic (gray)
As
33
74.9216
5.73
817
603
14
Albertus Magnus
1250
Astatine
At
85
2102

302

21
Corson et al.
1940
Barium
Ba
56
137.327
3.5
727
1897
25
Davy
1808
Berkelium
Bk
97
2472
14.006
1050 (α form)

84
Seaborg et al.
1949
Beryllium
Be
4
9.012182
1.848
1287
2471
6
Vauquelin
1798
Bismuth
Bi
83
208.98038
9.747
271.40
1564
19
Geoffroy the Younger
1753
Bohrium
Bh
107
2642




Armbruster and Münzenberg
1981
Boron
B
5
10.811
2.377
2075
4000
6
Gay-Lussac and
Thénard; Davy
1808
Bromine
Br
35
79.904
3.125
-7.2
58.8
19
Balard
1826
Cadmium
Cd
48
112.411
8.65
321.07
767
22
Stromeyer
1817
Calcium
Ca
20
40.078
1.55
842
1484
14
Davy
1808
Californium
Cf
98
2512

900

124
Seaborg et al.
1950
Carbon
C
6
12.0107
1.8–3.58
4492 (graphite)
3825
7
Prehistoric

Cerium
Ce
58
140.116
6.771
798
3443
19
Berzelius and Hisinger; Klaproth
1803
Cesium
Cs
55
132.90545
1.873
28.5
671
22
Bunsen and Kirchoff
1860
Chlorine
Cl
17
35.453
1.565
-101.5
-34.04
11
Scheele
1774
Chromium
Cr
24
51.9961
7.18-7.20
1907
2671
9
Vauquelin
1797
Cobalt
Co
27
58.9332
8.9
1495
2927
14
Brandt
c.1735
Copper
Cu
29
63.546
8.96
1084.62
2562
11
Prehistoric

Curium
Cm
96
2472
13.513
1345
3100
134
Seaborg et al.
1944
Darmstadtium
Ds
110
2812




S. Hofmann et al.
1994
Dubnium
Db
105
2622




Ghiorso et al.
1970
Dysprosium
Dy
66
162.5
8.540
1412
2567
21
de Boisbaudran
1886
Einsteinium
Es
99
2522

860

124
Ghiorso et al.
1952
Erbium
Er
68
167.259
9.045
1529
2868
16
Mosander
1843
Europium
Eu
63
151.964
5.283
822
1529
21
Demarcay
1901
Fermium
Fm
100
2572

1527

104
Ghiorso et al.
1953
Fluorine
F
9
18.9984032
1.1085
-219.67
-188.12
6
Moissan
1886
Francium
Fr
87
2232

27

21
Perey
1939
Gadolinium
Gd
64
157.25
7.898
1313
3273
17
de Marignac
1880
Gallium
Ga
31
69.723
5.904
29.76
2204
14
de Boisbaudran
1875
Germanium
Ge
32
72.64
5.323
938.25
2833
17
Winkler
1886
Gold
Au
79
196.96655
19.32
1064.18
2856
21
Prehistoric

Hafnium
Hf
72
178.49
13.31
2233
4603
17
Coster and von Hevesy
1923
Hassium
Hs
108
2772




Armbruster and Münzenberg
1983
Helium
He
2
4.002602
0.17855
-272.2
-268.934
5
Janssen
1868
Holmium
Ho
67
164.93032
8.781
1474
2700
29
Delafontaine and Soret
1878
Hydrogen
H
1
1.00794
0.0705
-259.34
-252.87
3
Cavendish
1766
Indium
In
49
114.818
7.31
156.60
2072
34
Reich and Richter
1863
Iodine
I
53
126.90447
4.93
113.7
184.4
24
Courtois
1811
Iridium
Ir
77
192.217
22.42
2446
4428
25
Tennant
1804
Iron
Fe
26
55.845
7.894
1538
2861
10
Prehistoric

Krypton
Kr
36
83.8
3.7335
-157.38
-153.22
23
Ramsay and Travers
1898
Lanthanum
La
57
138.9055
6.166
918
3464
19
Mosander
1839
Lawrencium
Lr
103
2622

1627

204
Ghiorso et al.
1961
Lead
Pb
82
207.2
11.35
327.46
1749
29
Prehistoric

Lithium
Li
3
6.941
0.534
180.50
1342
5
Arfvedson
1817
Lutetium
Lu
71
174.967
9.835
1663
3402
22
Urbain/ von Welsbach
1907
Magnesium
Mg
12
24.305
1.738
650
1090
8
Black
1755
Manganese
Mn
25
54.938049
7.21–7.449
1246
2061
11
Gahn, Scheele, and
Bergman
1774
Meitnerium
Mt
109
2682




GSI, Darmstadt,
West Germany
1982
Mendelevium
Md
101
2582

827

34
Ghiorso et al.
1955
Mercury
Hg
80
200.59
13.546
-38.83
356.73
26
Prehistoric

Molybdenum
Mo
42
95.94
10.22
2623
4639
20
Scheele
1778
Neodymium
Nd
60
144.24
6.80 & 7.00410
1021
3074
16
von Welsbach
1885
Neon
Ne
10
20.1797
0.89990
(g/10°C/1 atm)
-248.59
-246.08
8
Ramsay and Travers
1898
Neptunium
Np
93
2372
20.25
644

154
McMillan and Abelson
1940
Nickel
Ni
28
58.6934
8.902
1455
2913
11
Cronstedt
1751
Niobium
(Columbium)
Nb
41
92.90638
8.57
2477
4744
24
Hatchett
1801
Nitrogen
N
7
14.0067
0.8085
-210.00
-195.79
8
Rutherford
1772
Nobelium
No
102
2592

827

74
Ghiorso et al.
1958
Osmium
Os
76
190.23
22.57
3033
5012
19
Tennant
1803
Oxygen
O
8
15.9994
1.145
-218.79
-182.95
8
Priestley/Scheele
1774
Palladium
Pd
46
106.42
12.02
1554.9
2963
21
Wollaston
1803
Phosphorous
(white)
P
15
30.973761
1.82
44.15
280.5
7
Brand
1669
Platinum
Pt
78
195.078
21.45
1768.4
3825
32
Ulloa/Wood
1735/1741
Plutonium
Pu
94
2442
19.84
640
3228
164
Seaborg et al.
1940
Polonium
Po
84
2092
9.32
254
962
34
Curie
1898
Potassium
K
19
39.0983
0.862
63.5
759
10
Davy
1807
Praseodymium
Pr
59
140.90765
6.772
931
3520
15
von Welsbach
1885
Promethium
Pm
61
1452

1042
3000
14
Marinsky et al.
1945
Protactinium
Pa
91
231.03588
15.373
1572

14
Hahn and Meitner
1917
Radium
Ra
88
2262
5.0?
700

15
Pierre and Marie Curie
1898
Radon
Rn
86
2222
4.45
-71
-61.7
20
Dorn
1900
Rhenium
Re
75
186.207
21.02
3186
5596
21
Noddack, Berg, and Tacke
1925
Rhodium
Rh
45
102.9055
12.41
1964
3695
20
Wollaston
1803
Roentgenium10
Rg
111
2722




Hofmann et al.
1994
Rubidium
Rb
37
85.4678
1.532
39.30
688
20
Bunsen and Kirchoff
1861
Ruthenium
Ru
44
101.07
12.44
2334
4150
16
Klaus
1844
Rutherfordium
Rf
104
2612




Ghiorso et al.
1969
Samarium
Sm
62
150.36
7.536
1074
1794
17
Boisbaudran
1879
Scandium
Sc
21
44.95591
2.989
1541
2836
15
Nilson
1878
Seaborgium
Sg
106
2662




Ghiorso et al.
1974
Selenium
(gray)
Se
34
78.96
4.79
220.5
685
20
Berzelius
1817
Silicon
Si
14
28.0855
2.33
1414
3265
8
Berzelius
1824
Silver
Ag
47
107.8682
10.5
961.78
2162
27
Prehistoric

Sodium
Na
11
22.98977
0.971
97.80
883
7
Davy
1807
Strontium
Sr
38
87.62
2.54
777
1382
18
Davy
1808
Sulfur
S
16
32.065
2.0710
95.3 (rhombic)
444.60
10
Prehistoric

Tantalum
Ta
73
180.9479
16.654
3017
5458
19
Ekeberg
1801
Technetium
Tc
43
982
11.503
2157
4265
23
Perrier and Segré
1937
Tellurium
Te
52
127.60
6.24
449.51
988
29
von Reichenstein
1782
Terbium
Tb
65
158.92534
8.234
1356
3230
24
Mosander
1843
Thallium
Tl
81
204.3833
11.85
304
1473
28
Crookes
1861
Thorium
Th
90
232.0381
11.72
1750
4788
12
Berzelius
1828
Thulium
Tm
69
168.93421
9.314
1545
1950
18
Cleve
1879
Tin (white)
Sn
50
118.71
7.31
231.93
2602
28
Prehistoric

Titanium
Ti
22
47.867
4.55
1668
3287
9
Gregor
1791
Tungsten
W
74
183.84
19.3
3422
5555
22
J. and F. d'Elhuyar
1783
Uranium
U
92
238.02891
19.05
1135
4131
15
Peligot
1841
Vanadium
V
23
50.9415
6.11
1910
3407
9
del Rio
1801
Xenon
Xe
54
131.293
3.525
-111.79
-108.12
31
Ramsay and Travers
1898
Ytterbium
Yb
70
173.04
6.972
819
1196
16
Marignac
1878
Yttrium
Y
39
88.90585
4.457
1522
3345
21
Gadolin
1794
Zinc
Zn
30
65.39
7.133
419.5
907
15
Prehistoric

Zirconium
Zr
40
91.224
6.5063
1855






Chemical Element


A chemical element is a pure Chemical substancece consisting of one type of atom distinguished by atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. Common examples of elements are iron, cooper, silver, gold, hydrogen, carbon, nitrogen, and oxygen. In total, 117 elements have been observed as of 2008, of which 94 occur naturally on Earth. 80 elements have stable isotopes, namely all elements with atomic numbers 1 to 82, except elements 43 and 61 . Elements with atomic numbers 83 or higher are inherently unstable, and undergo radiactive deacay. The elements from atomic number 83 to 94 have no stable nuclei, but are nevertheless found in nature, either surviving as remnants of the primordial stell a nucleosynthesis that produced the elements in the solar system, or else produced as short-lived daughter-isotopes through the natural decay of uranium and thorium.
All chemical matter consists of these elements. New elements of higher atomic number are discovered from time to time, as products of artificial nuclear reactions.
This is the peridic table

external image 450px-Periodic_table.svg.png

DESCRIPTIONS:
Atomic number The atomic number of an element is z, is equal to the number of protons that defines the element. For example, all carbon atoms contain 6 protons in their nucleus so the atomic number "Z" of carbon is 6. Carbon atoms may have different numbers of neutrons, which are known as isotopes of the element.
The number of protons in the atomic nucleus also determines its electric charge, which in turn determines the electrones of the atom in its non ionaized state. This in turn determines the atom's various chemical propierties. So all carbon atoms, for example, ultimately have identical chemical properties because they all have the same number of protons in their nucleus, and therefore have the same atomic number. It is for this reason that atomic number rather than mass number is considered the identifying characteristic of an element.



Isotopes:
:




Atomic mass

The mass number of an element, A, is the number of nucleons in the atomic nucleus. Different isotopes of a given element are distinguished by their mass numbers, which are conventionally written as a super-index on the left hand side of the atomic symbol (e.g., 238U).
The relative atomic mass of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance, relative to the atomic mass unit . This number may be a fraction that is not close to a whole number, due to the averaging process. On the other hand, the atomic mass of a pure isotope is quite close to its mass number. Whereas the mass number is a natural number, the atomic mass of a single isotope is a real number that is close to a natural number.

taken from:http://en.wikipedia.org/wiki/Chemical_element ,http://www.youtube.com/watch?v=Jdtt3LsodAQ

description

The lightest elements are hydrogen and helium, both theoretically created by Big Bang nucleosynthesis during the first 20 minutes of the universe in a ratio of around 3:1 by mass (approximately 12:1 by number of atoms). Almost all other elements found in nature, including some further hydrogen and helium created since then, were made by various natural or (at times) artificial methods of nucleo synthesis, including occasionally breakdown activities such as nuclear fission, alpha decay, cluster decay, and cosmic ray spallation.
As of 2008, there are 117 known elements (in this context, "known" means observed well enough, even from just a few decay products, to have been differentiated from any other element). Of these 117 elements, 94 occur naturally on Earth. Six of these occur in extreme trace quantities: technetium, atomic number 43; promethium, number 61; astatine, number 85; francium, number 87; neptunium, number 93; and plutonium, number 94. These 94 elements, and also possibly element 98 californium, have been detected in the universe at large, in the spectra of stars and also supernovae, where short-lived radioactive elements are newly being made.
The remaining 22 elements, not found on Earth or in astronomical spectra, have been derived artificially. All of the elements that are derived solely through artificial means are radioactive with very short half-lives; if any atoms of these elements were present at the formation of Earth, they are extremely likely to have already decayed, and if present in novae, have been in quantities too small to have been noted. Technetium was the first purportedly non-naturally occurring element to be synthesized, in 1937, although trace amounts of technetium have since been found in nature, and the element may have been discovered naturally in 1925. This pattern of artificial production and later natural discovery has been repeated with several other radioactive naturally occurring trace elements.

Lists of the elements are available by name, by symbol, by atomic number, by density, by melting point, and by boiling point as well as Ionization energies of the elements. The most convenient presentation of the elements is in the periodic table, which groups elements with similar chemical properties together.




Allotropes

Atoms of pure elements may bond to each other chemically in more than one way, allowing the pure element to exist in multiple structures spacial arrangements of atoms, known as allotropes , which differ in their properties. For example, carbon can be found as diamond , which has a tetrahedral structure around each carbon atom; graphite, which has layers of carbon atoms with a hexagonal structure stacked on top of each other; grafhene, which is a single layer of graphite that is incredibly strong; fullerenes, which have nearly spherical shapes; and carbon nanotubes, which are tubes with a hexagonal structure even these may differ from each other in electrical properties. The ability for an element to exist in one of many structural forms is known as allotropy.



Standard state

The standard state, or reference state, of an element is defined as its thermodynamically most stable state at 1 bar at a given temperature typically at 298.15 K. In thermochemistry, an element is defined to have an enthalpy of formation of zero in its standard state. For example, the reference state for carbon is graphite, because it is more stable than the other allotropes.

external image 3d-chemical-elements-screensaver.jpg
http://en.wikipedia.org/wiki/Chemical_element

Pure Substance​

a pure substance is any substance that has a fixed composition and definite properties recognizable features. the values of specific properties of substances such as density and melting point.


chemical element
a chemical element is a pure substance can not be decomposed to simpler substances .the chemical elements come together to form compounds such as H20, this means that when you meet the oxygen and hydrogen, oxygen takes 2 electrons from hydrogen. There are many elements about 118 items to display in this video



these are organized in the periodic table according to the number of electrons. some of the elements found in nature but others are created in the lab any of these are: ununquadium, ununoctium.





chemical elements

Atomic number

The atomic number of an element, Z, is equal to the number of protons that defines the element. For example, all carbon atoms contain 6 protons in their nucleus; so the atomic number "Z" of carbon is 6. Carbon atoms may have different numbers of neutrons, which are known as isotopes of the element.
The number of protons in the atomic nucleus also determines its electric charge, which in turn determines the electrons of the atom in its non-ionized state. This in turn (by means of the Pauli exclusion principle) determines the atom's various chemical properties. So all carbon atoms, for example, ultimately have identical chemical properties because they all have the same number of protons in their nucleus, and therefore have the same atomic number. It is for this reason that atomic number rather than mass number (or atomic weight) is considered the identifying characteristic of an element.




Atomic mass

The mass number of an element, A, is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes of a given element are distinguished by their mass numbers, which are conventionally written as a super-index on the left hand side of the atomic symbol (e.g., 238U).
The relative atomic mass of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance, relative to the atomic mass unit (u). This number may be a fraction that is not close to a whole number, due to the averaging process. On the other hand, the atomic mass of a pure isotope is quite close to its mass number. Whereas the mass number is a natural (or whole) number, the atomic mass of a single isotope is a real number that is close to a natural number. In general, it differs slightly from the mass number as the mass of the protons and neutrons is not exactly 1 u, the electrons also contribute slightly to the atomic mass, and because of the nuclear binding energy. For example, the mass of 19F is 18.9984032 u. The only exception to the atomic mass of an isotope not being a natural number is 12C, which has a mass of
exactly 12, due to the definition of u// (it is fixed as 1/12th of the mass of a free carbon-12 atom, exactly).
taken from:http://en.wikipedia.org/wiki/Chemical_element


-What is a chemical element?
A chemical element, or an element, is a material which cannot be broken down or changed into another substance using chemical means. Elements may be thought of as the basic chemical building blocks of matter. Depending on how much evidence you require to prove a new element has been created, there are 117 or 118 known elements.

table of the elements.


I
II

III
IV
V
VI
VII
VIII
1
H1





He2
2
Li3
Be4

B5
C6
N7
O8
F9
Ne10
3
Na11
Mg12
Al13
Si14
P15
S16
Cl17
Ar18
4
K19
Ca20
Sc21
Ti22
V23
Cr24
Mn25
Fe26
Co27
Ni28
Cu29
Zn30
Ga31
Ge32
As33
Se34
Br35
Kr36
5
Rb37
Sr38
Y39
Zr40
Nb41
Mo42
Tc43
Ru44
Rh45
Pd46
Ag47
Cd48
In49
Sn50
Sb51
Te52
I53
Xe54
6
Cs55
Ba56
La57
Hf72
Ta73
W74
Re75
Os76
Ir77
Pt78
Au79
Hg80
Tl81
Pb82
Bi83
Po84
At85
Rn86
7
Fr87
Ra88
Ac89
Rf
104

Db
105

Sg
106

Bh
107

Hs
108

Mt
109

Ds
110

Rg
111

Uub
112

Uut
113

Uuq
114

UUp
115

Uuh
116

Uus
117

Uuo
118





Ce58
Pr59
Nd60
Pm61
Sm62
Eu63
Gd64
Tb65
Dy66
Ho67
Er68
Tm69
Yb70
Lu71






Th90
Pa91
U92
Np93
Pu94
Am95
Cm96
Bk97
Cf98
Es99
Fm100
Md101
No102
Lr103




taken from:

http://chemistry.about.com/od/chemistryfaqs/f/element.htm
http://www.lenntech.com/periodic/periodic-chart.htm

A

B

C

D

E

F

G

H

I

K

L

M

M cont.

N

O

P

R

S

taken from: http://en.wikipedia.org/wiki/Category:Chemical_elements