We explain what the atomic number is and its relationship with the atomic mass. Also, the atomic number of each chemical element.
What is the atomic number?
Both in physical like in chemistry, the atomic number is the total number of protons that make up the atomic nucleus of a chemical element determined.
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 (number of nucleons in the nucleus, that is, the sum of the number of protons and the number of neutrons). For example:
2311Na (element: sodium, atomic number: 11, and mass number: 23).
All the atoms they are composed of subatomic particles: some are part of its nucleus (protons Y neutrons) and others revolve around it (electrons). Protons are positively charged, neutrons are neutrally charged, and electrons are negatively charged (electrons).
Since atoms in nature are electrically neutral, the number of positive and negative particles is the same, so if an atom has Z = 11, it will have eleven protons and eleven electrons around it.
In addition, the atomic number allows to organize the known elements in the Periodic table, they go from the smallest to the largest number of protons in the nucleus as you proceed through the rows and columns of the table. For example, hydrogen (H) has just one proton (Z = 1), while oganeson (Og) has one hundred and eighteen (Z = 118). Thus you can differentiate light elements from heavy elements.
Atomic number examples
These are the atomic numbers of the complete Periodic Table:
| Hydrogen (H): Z = 1 | Helium (He): Z = 2 |
| Lithium (Li): Z = 3 | Beryllium (Be): Z = 4 |
| Boron (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 | Chromium (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 |
| Yttrium (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 |
| Indian (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 |
| Promethian (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 |
| Thulium (Tm): Z = 69 | Ytterbium (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 |
| Astat (At): Z = 85 | Radon (Rn): Z = 86 |
| Francium (Fr): Z = 87 | Radius (Ra): Z = 88 |
| Actinium (Ac): Z = 89 | Thorium (Th): Z = 90 |
| Proactinium (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 |
| Mendelevium (Md): Z = 101 | Nobelium (No): Z = 102 |
| Laurencio (Lr): Z = 103 | Rutherfordium (Rf): Z = 104 |
| Dubnium (Db): Z = 105 | Seaborgio (Sg): Z = 106 |
| Bohrio (Bh): Z = 107 | Hasio (Hs): Z = 108 |
| Meitnerium (Mt): Z = 109 | Darmstatio (Ds): Z = 110 |
| Roentgenium (Rg): Z = 111 | Copernicium (Cn): Z = 112 |
| Nihomium (Nh): Z = 113 | Flerovio (Fl): Z = 114 |
| Moscovio (Mc): Z = 115 | Livermorio (Lv): Z = 116 |
| Tenese (Ts): Z = 117 | Oganeson (Og): Z = 118 |
Mass number and atomic mass
The periodic table lists the atomic mass of the most stable isotope.The mass number is the sum of the protons and the neutrons. It is denoted by the letter A (from the German Atomgewicht) as a superscript to the left of the chemical symbol (for example: 23Na).
The mass number is usually approximately twice the atomic number since neutrons provide stability to the atomic nucleus, thus overcoming the natural repulsion between positively charged protons. Unlike the atomic number, the mass number varies in each isotope.
The mass number can be calculated according to the formula:
Mass number (A) = atomic number (Z) + number of neutrons (N).
Mass number should not be confused with atomic mass. Atomic mass is measured in units of CU (atomic mass unit) or Da (dalton). This unit is calculated from the carbon atom and each u.m.a is one twelfth of its mass. The periodic table lists the atomic mass of the most stable isotope.