Relative atomic mass

Relative Atomic Mass[edit | edit source]

The relative atomic mass (also known as atomic weight) of an element is a measure of the mass of its atoms relative to the mass of a carbon-12 atom, which is defined as exactly 12 atomic mass units (amu). This value is a dimensionless quantity, as it is a ratio of two masses.

Periodic Table by Atomic Weight[edit | edit source]

The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties. Elements are presented in order of increasing atomic number. The standard form of the periodic table includes the elements' relative atomic masses.

Calculation of Relative Atomic Mass[edit | edit source]

The relative atomic mass of an element is calculated as the weighted average of the atomic masses of its naturally occurring isotopes. The formula used is:

\[ \text{Relative Atomic Mass} = \sum ( \text{isotope abundance} \times \text{isotope mass} ) \]

For example, the relative atomic mass of chlorine is calculated using the masses and abundances of its two stable isotopes, chlorine-35 and chlorine-37.

Importance in Chemistry[edit | edit source]

Relative atomic mass is crucial in stoichiometry, which involves the calculation of reactants and products in chemical reactions. It is also essential in determining the molar mass of compounds, which is used in various chemical calculations.

Related Pages[edit | edit source]

Group	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
	Hydrogen & alkali metals	Alkaline earth metals											Triels	Tetrels	Pnictogens	Chalcogens	Halogens	Noble gases
Period 1	[[ hydrogen \|Hydrogen1H1.0080]]																	[[ helium \|Helium2He4.0026]]
2	[[ lithium \|Lithium3Li6.94]]	[[ beryllium \|Beryllium4Be9.0122]]											[[ boron \|Boron5B10.81]]	[[ carbon \|Carbon6C12.011]]	[[ nitrogen \|Nitrogen7N14.007]]	[[ oxygen \|Oxygen8O15.999]]	[[ fluorine \|Fluorine9F18.998]]	[[ neon \|Neon10Ne20.180]]
3	[[ sodium \|Sodium11Na22.990]]	[[ magnesium \|Magnesium12Mg24.305]]											[[ aluminium \|Aluminium13Al26.982]]	[[ silicon \|Silicon14Si28.085]]	[[ phosphorus\|Phosphorus15P30.974]]	[[ sulfur \|Sulfur16S32.06]]	[[ chlorine \|Chlorine17Cl35.45]]	[[ argon \|Argon18Ar39.95]]
4	[[ potassium \|Potassium19K39.098]]	[[ calcium \|Calcium20Ca40.078]]	[[ scandium \|Scandium21Sc44.956]]	[[ titanium \|Titanium22Ti47.867]]	[[ vanadium \|Vanadium23V50.942]]	[[ chromium \|Chromium24Cr51.996]]	[[ manganese \|Manganese25Mn54.938]]	[[ iron \|Iron26Fe55.845]]	[[ cobalt \|Cobalt27Co58.933]]	[[ nickel \|Nickel28Ni58.693]]	[[ copper \|Copper29Cu63.546]]	[[ zinc \|Zinc30Zn65.38]]	[[ gallium \|Gallium31Ga69.723]]	[[ germanium \|Germanium32Ge72.630]]	[[ arsenic \|Arsenic33As74.922]]	[[ selenium \|Selenium34Se78.971]]	[[ bromine \|Bromine35Br79.904]]	[[ krypton \|Krypton36Kr83.798]]
5	[[ rubidium \|Rubidium37Rb85.468]]	[[ strontium \|Strontium38Sr87.62]]	[[ yttrium \|Yttrium39Y88.906]]	[[ zirconium \|Zirconium40Zr91.224]]	[[ niobium \|Niobium41Nb92.906]]	[[ molybdenum\|Molybdenum42Mo95.95]]	[[ technetium\|Technetium43Tc[97]]]	[[ ruthenium \|Ruthenium44Ru101.07]]	[[ rhodium \|Rhodium45Rh102.91]]	[[ palladium \|Palladium46Pd106.42]]	[[ silver \|Silver47Ag107.87]]	[[ cadmium \|Cadmium48Cd112.41]]	[[ indium \|Indium49In114.82]]	[[ tin \|Tin50Sn118.71]]	[[ antimony \|Antimony51Sb121.76]]	[[ tellurium \|Tellurium52Te127.60]]	[[ iodine \|Iodine53I126.90]]	[[ xenon \|Xenon54Xe131.29]]
6	[[ caesium \|Caesium55Cs132.91]]	[[ barium \|Barium56Ba137.33]]	[[ lutetium \|Lutetium71Lu174.97]]	[[ hafnium \|Hafnium72Hf178.49]]	[[ tantalum \|Tantalum73Ta180.95]]	[[ tungsten \|Tungsten74W183.84]]	[[ rhenium \|Rhenium75Re186.21]]	[[ osmium \|Osmium76Os190.23]]	[[ iridium \|Iridium77Ir192.22]]	[[ platinum \|Platinum78Pt195.08]]	[[ gold \|Gold79Au196.97]]	[[ Mercury (element)\|Mercury80Hg200.59]]	[[ thallium \|Thallium81Tl204.38]]	[[ lead \|Lead82Pb207.2]]	[[ bismuth \|Bismuth83Bi208.98]]	[[ polonium \|Polonium84Po[209]]]	[[ astatine \|Astatine85At[210]]]	[[ radon \|Radon86Rn[222]]]
7	[[ francium \|Francium87Fr[223]]]	[[ radium \|Radium88Ra[226]]]	[[ lawrencium \|Lawrencium103Lr[266]]]	[[ rutherfordium\|Rutherfordium104Rf[267]]]	[[ dubnium \|Dubnium105Db[268]]]	[[ seaborgium \|Seaborgium106Sg[269]]]	[[ bohrium \|Bohrium107Bh[270]]]	[[ hassium \|Hassium108Hs[269]]]	[[ meitnerium \|Meitnerium109Mt[278]]]	[[ darmstadtium \|Darmstadtium110Ds[281]]]	[[ roentgenium \|Roentgenium111Rg[282]]]	[[ copernicium \|Copernicium112Cn[285]]]	[[ nihonium \|Nihonium113Nh[286]]]	[[ flerovium \|Flerovium114Fl[289]]]	[[ moscovium \|Moscovium115Mc[290]]]	[[ livermorium \|Livermorium116Lv[293]]]	[[ tennessine \|Tennessine117Ts[294]]]	[[ oganesson \|Oganesson118Og[294]]]

			[[ lanthanum \|Lanthanum57La138.91]]	[[ cerium \|Cerium58Ce140.12]]	[[ praseodymium\|Praseodymium59Pr140.91]]	[[ neodymium \|Neodymium60Nd144.24]]	[[ promethium \|Promethium61Pm[145]]]	[[ samarium \|Samarium62Sm150.36]]	[[ europium \|Europium63Eu151.96]]	[[ gadolinium \|Gadolinium64Gd157.25]]	[[ terbium \|Terbium65Tb158.93]]	[[ dysprosium \|Dysprosium66Dy162.50]]	[[ holmium \|Holmium67Ho164.93]]	[[ erbium \|Erbium68Er167.26]]	[[ thulium \|Thulium69Tm168.93]]	[[ ytterbium \|Ytterbium70Yb173.05]]
			[[ actinium \|Actinium89Ac[227]]]	[[ thorium \|Thorium90Th232.04]]	[[ protactinium\|Protactinium91Pa231.04]]	[[ uranium \|Uranium92U238.03]]	[[ neptunium \|Neptunium93Np[237]]]	[[ plutonium \|Plutonium94Pu[244]]]	[[ americium \|Americium95Am[243]]]	[[ curium \|Curium96Cm[247]]]	[[ berkelium \|Berkelium97Bk[247]]]	[[ californium \|Californium98Cf[251]]]	[[ einsteinium \|Einsteinium99Es[252]]]	[[ fermium \|Fermium100Fm[257]]]	[[ mendelevium\|Mendelevium101Md[258]]]	[[ nobelium \|Nobelium102No[259]]]

Primordial From decay Synthetic Border shows natural occurrence of the element

Standard atomic weight A_{r, std}(E)^[1]

Ca: 40.078

— Abridged value (uncertainty omitted here)^[2]

Po: [209] — mass number of the most stable isotope

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[CIAAW2013-1] Cite error: Invalid <ref> tag; no text was provided for refs named CIAAW2013

[CIAAW2021-2] Cite error: Invalid <ref> tag; no text was provided for refs named CIAAW2021

[1]

[2]

Group	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
	Hydrogen & alkali metals	Alkaline earth metals											Triels	Tetrels	Pnictogens	Chalcogens	Halogens	Noble gases
Period 1	[[ hydrogen \|Hydrogen1H1.0080]]																	[[ helium \|Helium2He4.0026]]
2	[[ lithium \|Lithium3Li6.94]]	[[ beryllium \|Beryllium4Be9.0122]]											[[ boron \|Boron5B10.81]]	[[ carbon \|Carbon6C12.011]]	[[ nitrogen \|Nitrogen7N14.007]]	[[ oxygen \|Oxygen8O15.999]]	[[ fluorine \|Fluorine9F18.998]]	[[ neon \|Neon10Ne20.180]]
3	[[ sodium \|Sodium11Na22.990]]	[[ magnesium \|Magnesium12Mg24.305]]											[[ aluminium \|Aluminium13Al26.982]]	[[ silicon \|Silicon14Si28.085]]	[[ phosphorus\|Phosphorus15P30.974]]	[[ sulfur \|Sulfur16S32.06]]	[[ chlorine \|Chlorine17Cl35.45]]	[[ argon \|Argon18Ar39.95]]
4	[[ potassium \|Potassium19K39.098]]	[[ calcium \|Calcium20Ca40.078]]	[[ scandium \|Scandium21Sc44.956]]	[[ titanium \|Titanium22Ti47.867]]	[[ vanadium \|Vanadium23V50.942]]	[[ chromium \|Chromium24Cr51.996]]	[[ manganese \|Manganese25Mn54.938]]	[[ iron \|Iron26Fe55.845]]	[[ cobalt \|Cobalt27Co58.933]]	[[ nickel \|Nickel28Ni58.693]]	[[ copper \|Copper29Cu63.546]]	[[ zinc \|Zinc30Zn65.38]]	[[ gallium \|Gallium31Ga69.723]]	[[ germanium \|Germanium32Ge72.630]]	[[ arsenic \|Arsenic33As74.922]]	[[ selenium \|Selenium34Se78.971]]	[[ bromine \|Bromine35Br79.904]]	[[ krypton \|Krypton36Kr83.798]]
5	[[ rubidium \|Rubidium37Rb85.468]]	[[ strontium \|Strontium38Sr87.62]]	[[ yttrium \|Yttrium39Y88.906]]	[[ zirconium \|Zirconium40Zr91.224]]	[[ niobium \|Niobium41Nb92.906]]	[[ molybdenum\|Molybdenum42Mo95.95]]	[[ technetium\|Technetium43Tc[97]]]	[[ ruthenium \|Ruthenium44Ru101.07]]	[[ rhodium \|Rhodium45Rh102.91]]	[[ palladium \|Palladium46Pd106.42]]	[[ silver \|Silver47Ag107.87]]	[[ cadmium \|Cadmium48Cd112.41]]	[[ indium \|Indium49In114.82]]	[[ tin \|Tin50Sn118.71]]	[[ antimony \|Antimony51Sb121.76]]	[[ tellurium \|Tellurium52Te127.60]]	[[ iodine \|Iodine53I126.90]]	[[ xenon \|Xenon54Xe131.29]]
6	[[ caesium \|Caesium55Cs132.91]]	[[ barium \|Barium56Ba137.33]]	[[ lutetium \|Lutetium71Lu174.97]]	[[ hafnium \|Hafnium72Hf178.49]]	[[ tantalum \|Tantalum73Ta180.95]]	[[ tungsten \|Tungsten74W183.84]]	[[ rhenium \|Rhenium75Re186.21]]	[[ osmium \|Osmium76Os190.23]]	[[ iridium \|Iridium77Ir192.22]]	[[ platinum \|Platinum78Pt195.08]]	[[ gold \|Gold79Au196.97]]	[[ Mercury (element)\|Mercury80Hg200.59]]	[[ thallium \|Thallium81Tl204.38]]	[[ lead \|Lead82Pb207.2]]	[[ bismuth \|Bismuth83Bi208.98]]	[[ polonium \|Polonium84Po[209]]]	[[ astatine \|Astatine85At[210]]]	[[ radon \|Radon86Rn[222]]]
7	[[ francium \|Francium87Fr[223]]]	[[ radium \|Radium88Ra[226]]]	[[ lawrencium \|Lawrencium103Lr[266]]]	[[ rutherfordium\|Rutherfordium104Rf[267]]]	[[ dubnium \|Dubnium105Db[268]]]	[[ seaborgium \|Seaborgium106Sg[269]]]	[[ bohrium \|Bohrium107Bh[270]]]	[[ hassium \|Hassium108Hs[269]]]	[[ meitnerium \|Meitnerium109Mt[278]]]	[[ darmstadtium \|Darmstadtium110Ds[281]]]	[[ roentgenium \|Roentgenium111Rg[282]]]	[[ copernicium \|Copernicium112Cn[285]]]	[[ nihonium \|Nihonium113Nh[286]]]	[[ flerovium \|Flerovium114Fl[289]]]	[[ moscovium \|Moscovium115Mc[290]]]	[[ livermorium \|Livermorium116Lv[293]]]	[[ tennessine \|Tennessine117Ts[294]]]	[[ oganesson \|Oganesson118Og[294]]]

			[[ lanthanum \|Lanthanum57La138.91]]	[[ cerium \|Cerium58Ce140.12]]	[[ praseodymium\|Praseodymium59Pr140.91]]	[[ neodymium \|Neodymium60Nd144.24]]	[[ promethium \|Promethium61Pm[145]]]	[[ samarium \|Samarium62Sm150.36]]	[[ europium \|Europium63Eu151.96]]	[[ gadolinium \|Gadolinium64Gd157.25]]	[[ terbium \|Terbium65Tb158.93]]	[[ dysprosium \|Dysprosium66Dy162.50]]	[[ holmium \|Holmium67Ho164.93]]	[[ erbium \|Erbium68Er167.26]]	[[ thulium \|Thulium69Tm168.93]]	[[ ytterbium \|Ytterbium70Yb173.05]]
			[[ actinium \|Actinium89Ac[227]]]	[[ thorium \|Thorium90Th232.04]]	[[ protactinium\|Protactinium91Pa231.04]]	[[ uranium \|Uranium92U238.03]]	[[ neptunium \|Neptunium93Np[237]]]	[[ plutonium \|Plutonium94Pu[244]]]	[[ americium \|Americium95Am[243]]]	[[ curium \|Curium96Cm[247]]]	[[ berkelium \|Berkelium97Bk[247]]]	[[ californium \|Californium98Cf[251]]]	[[ einsteinium \|Einsteinium99Es[252]]]	[[ fermium \|Fermium100Fm[257]]]	[[ mendelevium\|Mendelevium101Md[258]]]	[[ nobelium \|Nobelium102No[259]]]