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The atomic number Z or nuclear charge number of a chemical element is defined as the number of protons in its atomic nucleus [1]. In symbol notation, the atomic number Z is placed in front of the element symbol E as an index: ZE.
In addition to this clear definition, the atomic number contains the following additional information:
* The atomic number corresponds to the nuclear charge number of the atomic nucleus, since the protons carry a positive charge.
* In an uncharged nucleus, the positive charges on the nucleus are balanced by the negative charges on the electrons; The atomic number is therefore equal to the number of electrons in an uncharged atom.
* The atomic number Z is related to the total number of nucleons A (mass number) and the number N of neutrons in the atomic nucleus via the equation A = Z + N.
* The atomic number clearly determines a chemical element. If two atomic nuclei have unequal mass numbers and/or unequal nucleon numbers but the same atomic number, these are different nuclides or isotopes of the same element.
* The atomic number determines the position and order of the chemical elements in the periodic table.
| H 1 | He 2 | ||||||||||||||||||||||||||||||
| Li 3 | Be 4 | B 5 | C 6 | N 7 | O 8 | F 9 | Ne 10 | ||||||||||||||||||||||||
| Na 11 | Mg 12 | Al 13 | Si 14 | P 15 | S 16 | Cl 17 | Ar 18 | ||||||||||||||||||||||||
| K 19 | Ca 20 | Sc 21 | Ti 22 | V 23 | Cr 24 | Mn 25 | Fe 26 | Co 27 | Ni 28 | Cu 29 | Zn 30 | Ga 31 | Ge 32 | As 33 | Se 34 | Br 35 | Kr 36 | ||||||||||||||
| Rb 37 | Sr 38 | Y 39 | Zr 40 | Nb 41 | Mo 42 | Tc 43 | Ru 44 | Rh 45 | Pd 46 | Ag 47 | Cd 48 | In 49 | Sn 50 | Sb 51 | Te 52 | I 53 | Xe 54 | ||||||||||||||
| Cs 55 | Ba 56 | La 57 | Ce 58 | Pr 59 | Nd 60 | Pm 61 | Sm 62 | Eu 63 | Gd 64 | Tb 65 | Dy 66 | Ho 67 | Er 68 | Tm 69 | Yb 70 | Lu 71 | Hf 72 | Ta 73 | W 74 | Re 75 | Os 76 | Ir 77 | Pt 78 | Au 79 | Hg 80 | Tl 81 | Pb 82 | Bi 83 | Po 84 | At 85 | Rn 86 |
| Fr 87 | Ra 88 | Ac 89 | Th 90 | Pa 91 | U 92 | Np 93 | Pu 94 | Am 95 | Cm 96 | Bk 97 | Cf 98 | Es 99 | Fm 100 | Md 101 | No 102 | Lr 103 | Rf 104 | Db 105 | Sg 106 | Bh 107 | Hs 108 | Mt 109 | Ds 110 | Rg 111 | Cn 112 | Nh 113 | Fl 114 | Mc 115 | Lv 116 | Ts 117 | Og 118 |
[1] - Atomic number: Definition im IUPAC Gold Book, DOI 10.1351/goldbook.A00499.
Last update: 2023-12-01
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