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Astronomy 2e · Front matter

The Chemical Elements

CC BY 4.0 · OpenStax · approximately 4 min read

Learning objectives

The Chemical Elements
Element Symbol Atomic Number Atomic WeightWhere mean atomic weights have not been well determined, the atomic mass numbers of the most stable isotopes are given in parentheses. Percentage of Naturally Occurring Elements in the Universe
Hydrogen H 1 1.008 75
Helium He 2 4.003 23
Lithium Li 3 6.94 6 × 10−7
Beryllium Be 4 9.012 1 × 10−7
Boron B 5 10.821 1 × 10−7
Carbon C 6 12.011 0.5
Nitrogen N 7 14.007 0.1
Oxygen O 8 15.999 1
Fluorine F 9 18.998 4 × 10−5
Neon Ne 10 20.180 0.13
Sodium Na 11 22.990 0.002
Magnesium Mg 12 24.305 0.06
Aluminum Al 13 26.982 0.005
Silicon Si 14 28.085 0.07
Phosphorus P 15 30.974 7 × 10−4
Sulfur S 16 32.06 0.05
Chlorine Cl 17 35.45 1 × 10−4
Argon Ar 18 39.948 0.02
Potassium K 19 39.098 3 × 10−4
Calcium Ca 20 40.078 0.007
Scandium Sc 21 44.956 3 × 10−6
Titanium Ti 22 47.867 3 × 10−4
Vanadium V 23 50.942 3 × 10−4
Chromium Cr 24 51.996 0.0015
Manganese Mn 25 54.938 8 × 10−4
Iron Fe 26 55.845 0.11
Cobalt Co 27 58.933 3 × 10−4
Nickel Ni 28 58.693 0.006
Copper Cu 29 63.546 6 × 10−6
Zinc Zn 30 65.38 3 × 10−5
Gallium Ga 31 69.723 1 × 10−6
Germanium Ge 32 72.630 2 × 10−5
Arsenic As 33 74.922 8 × 10−7
Selenium Se 34 78.971 3 × 10−6
Bromine Br 35 79.904 7 × 10−7
Krypton Kr 36 83.798 4 × 10−6
Rubidium Rb 37 85.468 1 × 10−6
’Strontium Sr 38 87.62 4 × 10−6
Yttrium Y 39 88.906 7 × 10−7
Zirconium Zr 40 91.224 5 × 10−6
Niobium Nb 41 92.906 2 × 10−7
Molybdenum Mo 42 95.95 5 × 10−7
Technetium Tc 43 (98) —
Ruthenium Ru 44 101.07 4 × 10−7
Rhodium Rh 45 102.906 6 × 10−8
Palladium Pd 46 106.42 2 × 10−7
Silver Ag 47 107.868 6 × 10−8
Cadmium Cd 48 112.414 2 × 10−7
Indium In 49 114.818 3 × 10−8
Tin Sn 50 118.710 4 × 10−7
Antimony Sb 51 121.760 4 × 10−8
Tellurium Te 52 127.60 9 × 10−7
Iodine I 53 126.904 1 × 10−7
Xenon Xe 54 131.293 1 × 10−6
Cesium Cs 55 132.905 8 × 10−8
Barium Ba 56 137.327 1 × 10−6
Lanthanum La 57 138.905 2 × 10−7
Cerium Ce 58 140.116 1 × 10−6
Praseodymium Pr 59 140.907 2 × 10−7
Neodymium Nd 60 144.242 1 × 10−6
Promethium Pm 61 (145) —
Samarium Sm 62 150.36 5 × 10−7
Europium Eu 63 151.964 5 × 10−8
Gadolinium Gd 64 157.25 2 × 10−7
Terbium Tb 65 158.925 5 × 10−8
Dysprosium Dy 66 162.500 2 × 10−7
Holmium Ho 67 164.930 5 × 10−8
Erbium Er 68 167.259 2 × 10−7
Thulium Tm 69 168.934 1 × 10−8
Ytterbium Yb 70 173.054 2 × 10−7
Lutetium Lu 71 174.967 1 × 10−8
Hafnium Hf 72 178.49 7 × 10−8
Tantalum Ta 73 180.948 8 × 10−9
Tungsten W 74 183.84 5 × 10−8
Rhenium Re 75 186.207 2 × 10−8
Osmium Os 76 190.23 3 × 10−7
Iridium Ir 77 192.217 2 × 10−7
Platinum Pt 78 195.084 5 × 10−7
Gold Au 79 196.967 6 × 10−8
Mercury Hg 80 200.592 1 × 10−7
Thallium TI 81 204.38 5 × 10−8
Lead Pb 82 207.2 1 × 10−6
Bismuth Bi 83 208.980 7 × 10−8
Polonium Po 84 (209) —
Astatine At 85 (210) —
Radon Rn 86 (222) —
Francium Fr 87 (223) —
Radium Ra 88 (226) —
Actinium Ac 89 (227) —
Thorium Th 90 232.038 4 × 10−8
Protactinium Pa 91 231.036 —
Uranium U 92 238.029 2 × 10−8
Neptunium Np 93 (237) —
Plutonium Pu 94 (244) —
Americium Am 95 (243) —
Curium Cm 96 (247) —
Berkelium Bk 97 (247) —
Californium Cf 98 (251) —
Einsteinium Es 99 (252) —
Fermium Fm 100 (257) —
Mendelevium Md 101 (258) —
Nobelium No 102 (259) —
Lawrencium Lr 103 (262) —
Rutherfordium Rf 104 (267) —
Dubnium Db 105 (268) —
Seaborgium Sg 106 (271) —
Bohrium Bh 107 (272) —
Hassium Hs 108 (270) —
Meitnerium Mt 109 (276) —
Darmstadtium Ds 110 (281) —
Roentgenium Rg 111 (280) —
Copernicium Cn 112 (285) —
Nihonium Nh 113 (284) —
Flerovium Fl 114 (289) —
Moskovium Mc 115 (288) —
Livermorium Lv 116 (293) —
Tennessine Ts 117 (294) —
Oganesson Og 118 (294) —
← The Brightest Twenty StarsThe Constellations →

Attribution. Astronomy 2e, OpenStax, Rice University, and the contributing authors credited in the book. Licensed under Creative Commons Attribution 4.0 International. Source revision 63157f370b of openstax/osbooks-astronomy (2026-02-02). CC BY 4.0. Original source ↗. Text edition of a pinned CC BY 4.0 source revision of the OpenStax book, converted from CNXML by the EvidenceHelix importer. Original prose, learning objectives, tables, exercises, glossary and captions are preserved; images are not copied (figures link to the original source and keep their credits). No new content was added. Later revisions of this book can carry different licence terms and are not used.

In this chapter Contents

  • Preface
  • How to Study for an Introductory Astronomy Class
  • Astronomy Websites, Images, and Apps
  • Scientific Notation
  • Units Used in Science
  • Some Useful Constants for Astronomy
  • Physical and Orbital Data for the Planets
  • Selected Moons of the Planets
  • Future Total Eclipses
  • The Nearest Stars, Brown Dwarfs, and White Dwarfs
  • The Brightest Twenty Stars
  • The Chemical Elements
  • The Constellations
  • Star Chart and Sky Event Resources

Source

OpenStax source file ↗

Illustrated original ↗

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