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# What is the atomic number?

We explain what the atomic number is and its relation to the atomic mass. In addition, the atomic number of each chemical element.

1. ### What is the atomic number?

In both physics and chemistry , the atomic number is the total number of protons that make up the atomic nucleus of a given chemical element.

It is usually denoted by the letter Z (from the German word zahl , “number”) and placed as a subscript to the left of the chemical symbol of the element in question, just below the mass number (A). As follows:

23 11 Na (element: sodium, atomic number: 11, and mass number: 23).

All atoms are composed of subatomic particles : some deposited in its nucleus ( protons and neutrons ) and others rotating around it ( electrons ). The former have a positive charge (protons) or neutral (neutrons) and the latter have a negative charge (electrons).

Since atoms in nature are electrically neutral, the amount of positive and negative particles is equivalent, so if an atom has Z = 11, it will have not only eleven protons, but the same number of electrons around it.

In addition, the atomic number allows to organize the known elements in the Periodic Table , going from the smallest to the largest number of protons in the nucleus. Thus, for example, hydrogen (H) has only one proton (Z = 1), while oganeson (Og) has one hundred eighteen (Z = 118). Thus, light elements can be distinguished from heavy elements.

1. ### Examples of atomic number

These are the atomic numbers of the complete Periodic Table:

 Hydrogen (H): Z = 1 (He): Z = 2 Lithium (Li): Z = 3 Beryllium (Be): Z = 4 (B): Z = 5 Carbon (C): Z = 6 Nitrogen (N): Z = 7 Oxygen (O): Z = 8 Fluorine (F): Z = 9 Neon (Ne): Z = 10 Sodium (Na): Z = 11 Magnesium (Mg): Z = 12 Aluminum (Al): Z = 13 Silicon (Si): Z = 14 Phosphorus (P): Z = 15 Sulfur (S): Z = 16 Chlorine (Cl): Z = 17 Argon (Ar): Z = 18 Potassium (K): Z = 19 Calcium (Ca): Z = 20 Scandium (Sc): Z = 21 Titanium (Ti): Z = 22 Vanadium (V): Z = 23 (Cr): Z = 24 Manganese (Mn): Z = 25 Iron (Fe): Z = 26 Cobalt (Co): Z = 27 Nickel (Ni): Z = 28 Copper (Cu): Z = 29 Zinc (Zn): Z = 30 Gallium (Ga): Z = 31 Germanium (Ge): Z = 32 Arsenic (As): Z = 33 Selenium (Se): Z = 34 Bromine (Br): Z = 35 Krypton (Kr): Z = 36 Rubidium (Rb): Z = 37 Strontium (Sr): Z = 38 (Y): Z = 39 Zirconium (Zr): Z = 40 Niobium (Ni): Z = 41 Molybdenum (Mb): Z = 42 Technetium (Tc): Z = 43 Ruthenium (Ru): Z = 44 Rhodium (Rh): Z = 45 Palladium (Pd): Z = 46 Silver (Ag): Z = 47 Cadmium (Cd): Z = 48 (In): Z = 49 Tin (Sn): Z = 50 Antimony (Sb): Z = 51 Tellurium (Te): Z = 52 Iodine (I): Z = 53 Xenon (Xe): Z = 54 Cesium (Cs): Z = 55 Barium (Ba): Z = 56 Lanthanum (La): Z = 57 Cerium (Ce): Z = 58 Praseodymium (Pr): Z = 59 Neodymium (Nd): Z = 60 Promethium (Pr): Z = 61 Samarium (Sm): Z = 62 Europium (Eu): Z = 63 Gadolinium (Gd): Z = 64 Terbium (Tb): Z = 65 Dysprosium (Dy): Z = 66 Holmium (Ho): Z = 67 Erbium (Er): Z = 68 (Tm): Z = 69 (Yb): Z = 70 Lutetium (Lu): Z = 71 Hafnium (Hf): Z = 72 Tantalum (Ta): Z = 73 Tungsten (W): Z = 74 Rhenium (Re): Z = 75 Osmium (Os): Z = 76 Iridium (Ir): Z = 77 Platinum (Pt): Z = 78 Gold (Au): Z = 79 Mercury (Hg): Z = 80 Thallium (Tl): Z = 81 Lead (Pb): Z = 82 Bismuth (Bi): Z = 83 Polonium (Po): Z = 84 (At): Z = 85 Radon (Rn): Z = 86 Francium (Fr): Z = 87 (Ra): Z = 88 Actinium (Ac): Z = 89 (Th): Z = 90 (Pa): Z = 91 Uranium (U): Z = 92 Neptunium (Np): Z = 93 Plutonium (Pu): Z = 94 Americium (Am): Z = 95 Curium (Cm): Z = 96 Berkelium (Bk): Z = 97 Californium (Cf): Z = 98 Einsteinium (Es): Z = 99 Fermium (Fm): Z = 100 (Md): Z = 101 Nobelium (No): Z = 102 (Lr): Z = 103 Rutherfordium (Rf): Z = 104 Dubnium (Db): Z = 105 Seaborgium (Sg): Z = 106 Bohrium (Bh): Z = 107 Hassium (Hs): Z = 108 Meitnerium (Mt): Z = 109 (Ds): Z = 110 (Rg): Z = 111 Copernicium (Cn): Z = 112 (Nh): Z = 113 (Fl): Z = 114 Moscovium  (Mc): Z = 115 (Lv): Z = 116 (Ts): Z = 117 Oganesson (Og): Z = 118