Mass Of Elements



Atomic and Molecular Weights

Mass

The subscripts in chemical formulas, and the coefficients in chemical equations represent exact quantities. (ce{H_2O}), for example, indicates that a water molecule comprises exactly two atoms of hydrogen and one atom of oxygen. The following equation:

[ ce{C3H8(g) + 5O2(g) rightarrow 3CO2(g) + 4H2O(l)} label{Eq1}]

not only tells us that propane reacts with oxygen to produce carbon dioxide and water, but that 1 molecule of propane reacts with 5 molecules of oxygen to produce 3 molecules of carbon dioxide and 4 molecules of water. Since counting individual atoms or molecules is a little difficult, quantitative aspects of chemistry rely on knowing the masses of the compounds involved.

Atoms of different elements have different masses. Early work on the separation of water into its constituent elements (hydrogen and oxygen) indicated that 100 grams of water contained 11.1 grams of hydrogen and 88.9 grams of oxygen:

[text{100 grams Water} rightarrow text{11.1 grams Hydrogen} + text{88.9 grams Oxygen} label{Eq2}]

Mass of elements chart

The remaining elements are trace elements, of which more than a dozen are thought on the basis of good evidence to be necessary for life. All of the mass of the trace elements put together (less than 10 grams for a human body) do not add up to the body mass of magnesium, the least common of the 11 non-trace elements. For example in the element oxygen, the atomic mass is 15.9994u so that would also mean that 1 mol of oxygen weighs 15.9994g. In 1mole of a substance there is a set number of atoms or molecules (6.022140857×10^23). Use the periodic table to determine the atomic mass of each element in the molecule. Multiply each element's atomic mass by the number of atoms of that element in the molecule. This number is represented by the subscript next to the element symbol in the molecular formula. Add these values together for each different atom in the molecule. Select elements and see the molar mass of the compound. Chemical formula (Hill notation) Molar mass (g/mol) Modify.

Later, scientists discovered that water was composed of two atoms of hydrogen for each atom of oxygen. Therefore, in the above analysis, in the 11.1 grams of hydrogen there were twice as many atoms as in the 88.9 grams of oxygen. Therefore, an oxygen atom must weigh about 16 times as much as a hydrogen atom:

[ dfrac{dfrac{88.9;g;Oxygen}{1; atom}}{dfrac{111;g;Hydrogen}{2;atoms}} = 16 label{Eq3}]

Hydrogen, the lightest element, was assigned a relative mass of '1', and the other elements were assigned 'atomic masses' relative to this value for hydrogen. Thus, oxygen was assigned an atomic mass of 16. We now know that a hydrogen atom has a mass of 1.6735 x 10-24 grams, and that the oxygen atom has a mass of 2.6561 X 10-23 grams. As we saw earlier, it is convenient to use a reference unit when dealing with such small numbers: the atomic mass unit. The atomic mass unit (amu) was not standardized against hydrogen, but rather, against the 12C isotope of carbon (amu = 12).

Thus, the mass of the hydrogen atom (1H) is 1.0080 amu, and the mass of an oxygen atom (16O) is 15.995 amu. Once the masses of atoms were determined, the amu could be assigned an actual value:

Mass Of Elements

1 amu = 1.66054 x 10-24grams conversely: 1 gram = 6.02214 x 1023amu

Click a column header, such as Name, to sort the table by that item.
SEENotes at the bottom of the Table.

Mass Of Elements In The Periodic Table

No.
Atomic
weight
NameSym.M.P.
(°C)
B.P.
(°C)
Density*
(g/cm3)
Earth
crust (%)*
Discovery
(Year)
Group*Electron configurationIonization
energy (eV)
11.008HydrogenH-259-2530.090.14177611s113.60
24.003HeliumHe-272-2690.181895181s224.59
36.941LithiumLi1801,3470.5318171[He] 2s15.39
49.012BerylliumBe1,2782,9701.8517972[He] 2s29.32
510.811BoronB2,3002,5502.34180813[He] 2s2 2p18.30
612.011CarbonC3,5004,8272.260.09ancient14[He] 2s2 2p211.26
714.007NitrogenN-210-1961.25177215[He] 2s2 2p314.53
815.999OxygenO-218-1831.4346.71177416[He] 2s2 2p413.62
918.998FluorineF-220-1881.700.03188617[He] 2s2 2p517.42
1020.180NeonNe-249-2460.90189818[He] 2s2 2p621.56
1122.990SodiumNa988830.972.7518071[Ne] 3s15.14
1224.305MagnesiumMg6391,0901.742.0817552[Ne] 3s27.65
1326.982AluminumAl6602,4672.708.07182513[Ne] 3s2 3p15.99
1428.086SiliconSi1,4102,3552.3327.69182414[Ne] 3s2 3p28.15
1530.974PhosphorusP442801.820.13166915[Ne] 3s2 3p310.49
1632.065SulfurS1134452.070.05ancient16[Ne] 3s2 3p410.36
1735.453ChlorineCl-101-353.210.05177417[Ne] 3s2 3p512.97
1839.948ArgonAr-189-1861.78189418[Ne] 3s2 3p615.76
1939.098PotassiumK647740.862.5818071[Ar] 4s14.34
2040.078CalciumCa8391,4841.553.6518082[Ar] 4s26.11
2144.956ScandiumSc1,5392,8322.9918793[Ar] 3d1 4s26.56
2247.867TitaniumTi1,6603,2874.540.6217914[Ar] 3d2 4s26.83
2350.942VanadiumV1,8903,3806.1118305[Ar] 3d3 4s26.75
2451.996ChromiumCr1,8572,6727.190.0417976[Ar] 3d5 4s16.77
2554.938ManganeseMn1,2451,9627.430.0917747[Ar] 3d5 4s27.43
2655.845IronFe1,5352,7507.875.05ancient8[Ar] 3d6 4s27.90
2758.933CobaltCo1,4952,8708.9017359[Ar] 3d7 4s27.88
2858.693NickelNi1,4532,7328.900.02175110[Ar] 3d8 4s27.64
2963.546CopperCu1,0832,5678.96ancient11[Ar] 3d10 4s17.73
3065.390ZincZn4209077.13ancient12[Ar] 3d10 4s29.39
3169.723GalliumGa302,4035.91187513[Ar] 3d10 4s2 4p16.00
3272.640GermaniumGe9372,8305.32188614[Ar] 3d10 4s2 4p27.90
3374.922ArsenicAs816135.72ancient15[Ar] 3d10 4s2 4p39.79
3478.960SeleniumSe2176854.79181716[Ar] 3d10 4s2 4p49.75
3579.904BromineBr-7593.12182617[Ar] 3d10 4s2 4p511.81
3683.800KryptonKr-157-1533.75189818[Ar] 3d10 4s2 4p614.00
3785.468RubidiumRb396881.6318611[Kr] 5s14.18
3887.620StrontiumSr7691,3842.5417902[Kr] 5s25.69
3988.906YttriumY1,5233,3374.4717943[Kr] 4d1 5s26.22
4091.224ZirconiumZr1,8524,3776.510.0317894[Kr] 4d2 5s26.63
4192.906NiobiumNb2,4684,9278.5718015[Kr] 4d4 5s16.76
4295.940MolybdenumMo2,6174,61210.2217816[Kr] 4d5 5s17.09
43*98.000TechnetiumTc2,2004,87711.5019377[Kr] 4d5 5s27.28
44101.070RutheniumRu2,2503,90012.3718448[Kr] 4d7 5s17.36
45102.906RhodiumRh1,9663,72712.4118039[Kr] 4d8 5s17.46
46106.420PalladiumPd1,5522,92712.02180310[Kr] 4d108.34
47107.868SilverAg9622,21210.50ancient11[Kr] 4d10 5s17.58
48112.411CadmiumCd3217658.65181712[Kr] 4d10 5s28.99
49114.818IndiumIn1572,0007.31186313[Kr] 4d10 5s2 5p15.79
50118.710TinSn2322,2707.31ancient14[Kr] 4d10 5s2 5p27.34
51121.760AntimonySb6301,7506.68ancient15[Kr] 4d10 5s2 5p38.61
52127.600TelluriumTe4499906.24178316[Kr] 4d10 5s2 5p49.01
53126.905IodineI1141844.93181117[Kr] 4d10 5s2 5p510.45
54131.293XenonXe-112-1085.90189818[Kr] 4d10 5s2 5p612.13
55132.906CesiumCs296781.8718601[Xe] 6s13.89
56137.327BariumBa7251,1403.590.0518082[Xe] 6s25.21
57138.906LanthanumLa9203,4696.1518393[Xe] 5d1 6s25.58
58140.116CeriumCe7953,2576.771803101[Xe] 4f1 5d1 6s25.54
59140.908PraseodymiumPr9353,1276.771885101[Xe] 4f3 6s25.47
60144.240NeodymiumNd1,0103,1277.011885101[Xe] 4f4 6s25.53
61*145.000PromethiumPm1,1003,0007.301945101[Xe] 4f5 6s25.58
62150.360SamariumSm1,0721,9007.521879101[Xe] 4f6 6s25.64
63151.964EuropiumEu8221,5975.241901101[Xe] 4f7 6s25.67
64157.250GadoliniumGd1,3113,2337.901880101[Xe] 4f7 5d1 6s26.15
65158.925TerbiumTb1,3603,0418.231843101[Xe] 4f9 6s25.86
66162.500DysprosiumDy1,4122,5628.551886101[Xe] 4f10 6s25.94
67164.930HolmiumHo1,4702,7208.801867101[Xe] 4f11 6s26.02
68167.259ErbiumEr1,5222,5109.071842101[Xe] 4f12 6s26.11
69168.934ThuliumTm1,5451,7279.321879101[Xe] 4f13 6s26.18
70173.040YtterbiumYb8241,4666.901878101[Xe] 4f14 6s26.25
71174.967LutetiumLu1,6563,3159.841907101[Xe] 4f14 5d1 6s25.43
72178.490HafniumHf2,1505,40013.3119234[Xe] 4f14 5d2 6s26.83
73180.948TantalumTa2,9965,42516.6518025[Xe] 4f14 5d3 6s27.55
74183.840TungstenW3,4105,66019.3517836[Xe] 4f14 5d4 6s27.86
75186.207RheniumRe3,1805,62721.0419257[Xe] 4f14 5d5 6s27.83
76190.230OsmiumOs3,0455,02722.6018038[Xe] 4f14 5d6 6s28.44
77192.217IridiumIr2,4104,52722.4018039[Xe] 4f14 5d7 6s28.97
78195.078PlatinumPt1,7723,82721.45173510[Xe] 4f14 5d9 6s18.96
79196.967GoldAu1,0642,80719.32ancient11[Xe] 4f14 5d10 6s19.23
80200.590MercuryHg-3935713.55ancient12[Xe] 4f14 5d10 6s210.44
81204.383ThalliumTl3031,45711.85186113[Xe] 4f14 5d10 6s2 6p16.11
82207.200LeadPb3271,74011.35ancient14[Xe] 4f14 5d10 6s2 6p27.42
83208.980BismuthBi2711,5609.75ancient15[Xe] 4f14 5d10 6s2 6p37.29
84*209.000PoloniumPo2549629.30189816[Xe] 4f14 5d10 6s2 6p48.42
85*210.000AstatineAt3023370.00194017[Xe] 4f14 5d10 6s2 6p59.30
86*222.000RadonRn-71-629.73190018[Xe] 4f14 5d10 6s2 6p610.75
87*223.000FranciumFr276770.0019391[Rn] 7s14.07
88*226.000RadiumRa7001,7375.5018982[Rn] 7s25.28
89*227.000ActiniumAc1,0503,20010.0718993[Rn] 6d1 7s25.17
90232.038ThoriumTh1,7504,79011.721829102[Rn] 6d2 7s26.31
91231.036ProtactiniumPa1,568015.401913102[Rn] 5f2 6d1 7s25.89
92238.029UraniumU1,1323,81818.951789102[Rn] 5f3 6d1 7s26.19
93*237.000NeptuniumNp6403,90220.201940102[Rn] 5f4 6d1 7s26.27
94*244.000PlutoniumPu6403,23519.841940102[Rn] 5f6 7s26.03
95*243.000AmericiumAm9942,60713.671944102[Rn] 5f7 7s25.97
96*247.000CuriumCm1,340013.5019441025.99
97*247.000BerkeliumBk986014.7819491026.20
98*251.000CaliforniumCf900015.1019501026.28
99*252.000EinsteiniumEs86000.0019521026.42
100*257.000FermiumFm1,52700.0019521026.50
101*258.000MendeleviumMd000.0019551026.58
102*259.000NobeliumNo82700.0019581026.65
103*262.000LawrenciumLr1,62700.0019611024.90
104*261.000RutherfordiumRf000.00196440.00
105*262.000DubniumDb000.00196750.00
106*266.000SeaborgiumSg000.00197460.00
107*264.000BohriumBh000.00198170.00
108*277.000HassiumHs000.00198480.00
109*268.000MeitneriumMt000.00198290.00
No.
Atomic
weight
NameSym.M.P.
(°C)
B.P.
(°C)
Density*
(g/cm3)
Earth crust
(%)*
Discovery
(Year)
Group*Electron configurationIonization
energy (eV)

Notes:
• Density of elements with boiling points below 0°C is given in g/l. In a sorted list, these elements are shown before other elements that have boiling points >0°C.
• Earth crust composition average values are from a report by F. W. Clarke and H. S. Washington, 1924. Elemental composition of crustal rocks differ between different localities (see article).
Group: There are only 18 groups in the periodic table that constitute the columns of the table. Lanthanoids and Actinoids are numbered as 101 and 102 to separate them in sorting by group.
• The elements marked with an asterisk (in the 2nd column) have no stable nuclides. For these elements the weight value shown represents the mass number of the longest-lived isotope of the element.

Abbreviations and Definitions:

No. - Atomic Number; M.P. - melting point; B.P. - boiling point

Periodic Table With Atomic Mass

Atomic number: The number of protons in an atom. Each element is uniquely defined by its atomic number.

Mass

Atomic mass: The mass of an atom is primarily determined by the number of protons and neutrons in its nucleus. Atomic mass is measured in Atomic Mass Units (amu) which are scaled relative to carbon, 12C, that is taken as a standard element with an atomic mass of 12. This isotope of carbon has 6 protons and 6 neutrons. Thus, each proton and neutron has a mass of about 1 amu.

Isotope: Atoms of the same element with the same atomic number, but different number of neutrons. Isotope of an element is defined by the sum of the number of protons and neutrons in its nucleus. Elements have more than one isotope with varying numbers of neutrons. For example, there are two common isotopes of carbon, 12C and 13C which have 6 and 7 neutrons respectively. The abundances of different isotopes of elements vary in nature depending on the source of materials. For relative abundances of isotopes in nature see reference on Atomic Weights and Isotopic Compositions.

Atomic weight: Atomic weight values represent weighted average of the masses of all naturally occurring isotopes of an element. The values shown here are based on the IUPAC Commission determinations (Pure Appl. Chem. 73:667-683, 2001). The elements marked with an asterisk have no stable nuclides. For these elements the weight value shown represents the mass number of the longest-lived isotope of the element.

Electron configuration: See next page for explanation of electron configuration of atoms.

Ionization energy (IE): The energy required to remove the outermost electron from an atom or a positive ion in its ground level. The table lists only the first IE in eV units. To convert to kJ/mol multiply by 96.4869. Reference: NIST Reference Table on Ground states and ionization energies for the neutral atoms. IE decreases going down a column of the periodic table, and increases from left to right in a row. Thus, alkali metals have the lowest IE in a period and Rare gases have the highest.

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