Element, aynı cins atomlardan oluşan ve kimyasal yollarla kendinden daha basit ve farklı maddelere ayrılamayan saf maddelere verilen isimdir.
Her farklı kimyasal element farklı atom numarasına sahiptir. Atom numarası atomdaki proton sayısını (çekirdek yükünü) gösteren sayıdır. Bir elementin böylece tüm atomlarında aynı sayıda proton bulunur. Proton sayıları aynı, nötron sayısı (kütle numaraları [= proton sayısı + nötron sayısı]) farklı atomlara izotop denir.1
Toplam 118 adet element bulunmuştur. Bunların 94 tanesi Dünya üzerinde doğal olarak bulunmaktadır. 80 adet element kararlı izotopa sahiptir. Bu elementler, atom numarası 43 ve 61 (teknetyum ve prometyum) dışında atom numarası 1'den 82'ye kadar olan atomlardır. Atom numarası 83 ve daha fazlası olan atomlar (bizmut ve fazlası) kesinlikle kararlı değildirler ve radyoaktif özellikler barındırırlar. Atom numarası 83'ten 94'e kadar olanlar kararlı değillerdir.
Bir element insan vücudunda yüzde miligram mertebesinde bulunursa bu elemente makroelement (majörelement, plastik element) denir. Diğerlerine nazaran daha az oranda (yüzde mikrogram mertebesinde) bulunanlara ise izelement (oligoelement, minörelement, katalitik element) adı verilir. Minörelementler genellikle enzim, hormon gibi vücutta önemli fonksiyonu olan maddelere bağlı olarak görev yaparlar.
Na<sup>+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, Mg<sup>2+</sup>, Cl<sup>-</sup>, HCO<sub>3</sub><sup>-</sup>, PO<sub>4</sub><sup>3-</sup>, HPO<sub>4</sub><sup>2-</sup> gibi iyonlar halinde bulunurlar. Elektrolit dengeyi sağlarlar. Ayrıca vücutta su dengesinin ve osmotik basıncın ayarlanması iyon halindeki elementlerle sağlanır.
Hemoglobinde, miyoglobinde demir (Fe) bulunur, çeşitli enzimlerin yapısında da metal iyonları bulunmaktadır. Bunların haricinde silisyum (Si), alüminyum (Al), kalay (Sn) ve arsenik (As) de az miktarda bulunabilir. Kurşun (Pb) ve kadmiyum (Cd) da yiyecek kapları ve kirli hava ile vücuda girebilir.
<TABLE ALIGN="center"> <TR> <TD> <TABLE BORDER="1" CELLSPACING="1" ALIGN="left"> <TR> <TD>'''<U>
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</TD> <TD>'''<U>
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</TD> </TR> <TR> <TD>1
</TD> <TD>H
</TD> <TD> </TD> </TR> <TR> <TD>2
</TD> <TD>He
</TD> <TD> </TD> </TR> <TR> <TD>3
</TD> <TD>Li
</TD> <TD> </TD> </TR> <TR> <TD>4
</TD> <TD>Be
</TD> <TD> </TD> </TR> <TR> <TD>5
</TD> <TD>B
</TD> <TD> </TD> </TR> <TR> <TD>6
</TD> <TD>C
</TD> <TD> </TD> </TR> <TR> <TD>7
</TD> <TD>N
</TD> <TD> </TD> </TR> <TR> <TD>8
</TD> <TD>O
</TD> <TD> </TD> </TR> <TR> <TD>9
</TD> <TD>F
</TD> <TD> </TD> </TR> <TR> <TD>10
</TD> <TD>Ne
</TD> <TD> </TD> </TR> <TR> <TD>11
</TD> <TD>Na
</TD> <TD> </TD> </TR> <TR> <TD>12
</TD> <TD>Mg
</TD> <TD> </TD> </TR> <TR> <TD>13
</TD> <TD>Al
</TD> <TD> </TD> </TR> <TR> <TD>14
</TD> <TD>Si
</TD> <TD> </TD> </TR> <TR> <TD>15
</TD> <TD>P
</TD> <TD> </TD> </TR> <TR> <TD>16
</TD> <TD>S
</TD> <TD> </TD> </TR> <TR> <TD>17
</TD> <TD>Cl
</TD> <TD> </TD> </TR> <TR> <TD>18
</TD> <TD>Ar
</TD> <TD> </TD> </TR> <TR> <TD>19
</TD> <TD>K
</TD> <TD> </TD> </TR> <TR> <TD>20
</TD> <TD>Ca
</TD> <TD> </TD> </TR> <TR> <TD>21
</TD> <TD>Sc
</TD> <TD> </TD> </TR> <TR> <TD>22
</TD> <TD>Ti
</TD> <TD> </TD> </TR> <TR> <TD>23
</TD> <TD>V
</TD> <TD> </TD> </TR> <TR> <TD>24
</TD> <TD>Cr
</TD> <TD> </TD> </TR> <TR> <TD>25
</TD> <TD>Mn
</TD> <TD> </TD> </TR> <TR> <TD>26
</TD> <TD>Fe
</TD> <TD> </TD> </TR> <TR> <TD>27
</TD> <TD>Co
</TD> <TD> </TD> </TR> <TR> <TD>28
</TD> <TD>Ni
</TD> <TD> </TD> </TR> <TR> <TD>29
</TD> <TD>Cu
</TD> <TD> </TD> </TR> <TR> <TD>30
</TD> <TD>Zn
</TD> <TD> </TD> </TR> <TR> <TD>31
</TD> <TD>Ga
</TD> <TD> </TD> </TR> <TR> <TD>32
</TD> <TD>Ge
</TD> <TD> </TD> </TR> <TR> <TD>33
</TD> <TD>As
</TD> <TD> </TD> </TR> <TR> <TD>34
</TD> <TD>Se
</TD> <TD> </TD> </TR> <TR> <TD>35
</TD> <TD>Br
</TD> <TD> </TD> </TR> <TR> <TD>36
</TD> <TD>Kr
</TD> <TD> </TD> </TR> <TR> <TD>37
</TD> <TD>Rb
</TD> <TD> </TD> </TR> <TR> <TD>38
</TD> <TD>Sr
</TD> <TD> </TD> </TR> <TR> <TD>39
</TD> <TD>Y
</TD> <TD> </TD> </TR> <TR> <TD>40
</TD> <TD>Zr
</TD> <TD> </TD> </TR> <TR> <TD>41
</TD> <TD>Nb
</TD> <TD> </TD> </TR> <TR> <TD>42
</TD> <TD>Mo
</TD> <TD> </TD> </TR> <TR> <TD>43
</TD> <TD>Tc
</TD> <TD> </TD> </TR> <TR> <TD>44
</TD> <TD>Ru
</TD> <TD> </TD> </TR> <TR> <TD>45
</TD> <TD>Rh
</TD> <TD> </TD> </TR> <TR> <TD>46
</TD> <TD>Pd
</TD> <TD> </TD> </TR> <TR> <TD>47
</TD> <TD>Ag
</TD> <TD> </TD> </TR> <TR> <TD>48
</TD> <TD>Cd
</TD> <TD> </TD> </TR> <TR> <TD>49
</TD> <TD>In
</TD> <TD> </TD> </TR> <TR> <TD>50
</TD> <TD>Sn
</TD> <TD> </TD> </TR> <TR> <TD>51
</TD> <TD>Sb
</TD> <TD> </TD> </TR> <TR> <TD>52
</TD> <TD>Te
</TD> <TD> </TD> </TR> <TR> <TD>53
</TD> <TD>I
</TD> <TD> </TD> </TR> <TR> <TD>54
</TD> <TD>Xe
</TD> <TD> </TD> </TR> <TR> <TD>55
</TD> <TD>Cs
</TD> <TD> </TD> </TR> <TR> <TD>56
</TD> <TD>Ba
</TD> <TD> </TD> </TR> <TR> <TD>57
</TD> <TD>La
</TD> <TD> </TD> </TR> <TR> <TD>58
</TD> <TD>Ce
</TD> <TD> </TD> </TR> <TR> <TD>59
</TD> <TD>Pr
</TD> <TD> </TD> </TR> <TR> <TD>60
</TD> <TD>Nd
</TD> <TD> </TD> </TR> </TD> </TABLE> </TD> <TD> <TABLE BORDER="1" CELLSPACING="1" ALIGN="right"> <TR> <TD>'''<U>
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</TD> </TR> <TR> <TD>61
</TD> <TD>Pm
</TD> <TD> </TD> </TR> <TR> <TD>62
</TD> <TD>Sm
</TD> <TD> </TD> </TR> <TR> <TD>63
</TD> <TD>Eu
</TD> <TD> </TD> </TR> <TR> <TD>64
</TD> <TD>Gd
</TD> <TD> </TD> </TR> <TR> <TD>65
</TD> <TD>Tb
</TD> <TD> </TD> </TR> <TR> <TD>66
</TD> <TD>Dy
</TD> <TD> </TD> </TR> <TR> <TD>67
</TD> <TD>Ho
</TD> <TD> </TD> </TR> <TR> <TD>68
</TD> <TD>Er
</TD> <TD> </TD> </TR> <TR> <TD>69
</TD> <TD>Tm
</TD> <TD> </TD> </TR> <TR> <TD>70
</TD> <TD>Yb
</TD> <TD> </TD> </TR> <TR> <TD>71
</TD> <TD>Lu
</TD> <TD> </TD> </TR> <TR> <TD>72
</TD> <TD>Hf
</TD> <TD> </TD> </TR> <TR> <TD>73
</TD> <TD>Ta
</TD> <TD> </TD> </TR> <TR> <TD>74
</TD> <TD>W
</TD> <TD> </TD> </TR> <TR> <TD>75
</TD> <TD>Re
</TD> <TD> </TD> </TR> <TR> <TD>76
</TD> <TD>Os
</TD> <TD> </TD> </TR> <TR> <TD>77
</TD> <TD>Ir
</TD> <TD> </TD> </TR> <TR> <TD>78
</TD> <TD>Pt
</TD> <TD> </TD> </TR> <TR> <TD>79
</TD> <TD>Au
</TD> <TD> </TD> </TR> <TR> <TD>80
</TD> <TD>Hg
</TD> <TD> </TD> </TR> <TR> <TD>81
</TD> <TD>Tl
</TD> <TD> </TD> </TR> <TR> <TD>82
</TD> <TD>Pb
</TD> <TD> </TD> </TR> <TR> <TD>83
</TD> <TD>Bi
</TD> <TD> </TD> </TR> <TR> <TD>84
</TD> <TD>Po
</TD> <TD> </TD> </TR> <TR> <TD>85
</TD> <TD>At
</TD> <TD> </TD> </TR> <TR> <TD>86
</TD> <TD>Rn
</TD> <TD> </TD> </TR> <TR> <TD>87
</TD> <TD>Fr
</TD> <TD> </TD> </TR> <TR> <TD>88
</TD> <TD>Ra
</TD> <TD> </TD> </TR> <TR> <TD>89
</TD> <TD>Ac
</TD> <TD> </TD> </TR> <TR> <TD>90
</TD> <TD>Th
</TD> <TD> </TD> </TR> <TR> <TD>91
</TD> <TD>Pa
</TD> <TD> </TD> </TR> <TR> <TD>92
</TD> <TD>U
</TD> <TD> </TD> </TR> <TR> <TD>93
</TD> <TD>Np
</TD> <TD> </TD> </TR> <TR> <TD>94
</TD> <TD>Pu
</TD> <TD> </TD> </TR> <TR> <TD>95
</TD> <TD>Am
</TD> <TD> </TD> </TR> <TR> <TD>96
</TD> <TD>Cm
</TD> <TD> </TD> </TR> <TR> <TD>97
</TD> <TD>Bk
</TD> <TD> </TD> </TR> <TR> <TD>98
</TD> <TD>Cf
</TD> <TD> </TD> </TR> <TR> <TD>99
</TD> <TD>Es
</TD> <TD> </TD> </TR> <TR> <TD>100
</TD> <TD>Fm
</TD> <TD> </TD> </TR> <TR> <TD>101
</TD> <TD>Md
</TD> <TD> </TD> </TR> <TR> <TD>102
</TD> <TD>No
</TD> <TD> </TD> </TR> <TR> <TD>103
</TD> <TD>Lr
</TD> <TD> </TD> </TR> <TR> <TD>104
</TD> <TD>Rf
</TD> <TD> </TD> </TR> <TR> <TD>105
</TD> <TD>Db
</TD> <TD> </TD> </TR> <TR> <TD>106
</TD> <TD>Sg
</TD> <TD> </TD> </TR> <TR> <TD>107
</TD> <TD>Bh
</TD> <TD> </TD> </TR> <TR> <TD>108
</TD> <TD>Hs
</TD> <TD> </TD> </TR> <TR> <TD>109
</TD> <TD>Mt
</TD> <TD> </TD> </TR> <TR> <TD>110
</TD> <TD>Ds
</TD> <TD> </TD> </TR> <TR> <TD>111
</TD> <TD>Rg
</TD> <TD> </TD> </TR> <TR> <TD>112
</TD> <TD>Cn
</TD> <TD> </TD> </TR> <TR> <TD>113
</TD> <TD>Nh
</TD> <TD> </TD> </TR> <TR> <TD>114
</TD> <TD>Fl
</TD> <TD> </TD> </TR> <TR> <TD>115
</TD> <TD>Mc
</TD> <TD> </TD> </TR> <TR> <TD>116
</TD> <TD>Lv
</TD> <TD> </TD> </TR> <TR> <TD>117*
</TD> <TD>Ts
</TD> <TD> </TD> </TR> <TR> <TD>118
</TD> <TD>Og
</TD> <TD> </TD> </TR> <TR> <TD>-
</TD> <TD>-
</TD> <TD>-
</TD> </TR> <TR> <TD>-
</TD> <TD>-
</TD> <TD>-
</TD> </TR> </TABLE> </TD> </TR> <TR> <TD ALIGN="Colspan" COLSPAN="2"> </TABLE>Orijinal kaynak: element. Creative Commons Atıf-BenzerPaylaşım Lisansı ile paylaşılmıştır.
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