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1. Atomic Mass And Number Worksheet

Molecular mass (molecular weight) is the mass of one molecule of a substance and is expressed in the unified atomic mass units (u). (1 u is equal to 1/12 the mass of one atom of carbon-12) Molar mass (molar weight) is the mass of one mole of a substance and is expressed in g/mol. Weights of atoms and isotopes are from NIST article. The standard atomic weight is a special value of the relative atomic mass. It is defined as the 'recommended values' of relative atomic masses of sources in the local environment of the Earth's crust and atmosphere as determined by the IUPAC Commission on Atomic Weights and Isotopic Abundances (CIAAW).

Isotope	Atomic mass (Da)	Isotopic abundance (amount fraction)
204Pb	203.973 043(8)	0.014(6)
206Pb	205.974 465(8)	0.241(30)
207Pb	206.975 897(8)	0.221(50)
208Pb	207.976 652(8)	0.524(70)

The atomic weight of lead is quite variable in nature because the three heaviest isotopes are the stableend-products of the radioactive decay of uranium (²³⁸U to ²⁰⁶Pb and ²³⁵U to ²⁰⁷Pb) and thorium (²³²Th to ²⁰⁸Pb). In fact, the variability of A_r(Pb) had been incontrovertibly shown before the discovery of isotopes andthe isotopic composition of common lead must now be regarded as a variable mixture of primeval and radiogenic components.

Recognizing this, in 1961, the Commission recommended an atomic weight of 207.19 that was based on the chemical measurements, and stated that '...it quite well represented the lead most likely to be encountered in normal laboratorywork'. However, the Commission's policy now aims for the implied range of the standard atomic weights to coverall normal sources of an element. In the 1969 report, the Commission considered natural variations in the atomic weight of lead rangingfrom 207.184 to 207.293 and recommended the value of A_r(Pb) = 207.2(1). These circumstancesjustify the annotation 'r'. In addition, the annotation 'g' warns of the existence of abnormal sources outside the implied range.

The decay of uranium and thorium to lead permits geological age determinations to be made of minerals containingthe heavy radioactive elements. Extensive use of lead over the history of mankind has led to widespread pollution, and the isotope-abundance variations reflected in the atomic weights enable historical and modern sources to be identified.

SOURCEAtomic weights of the elements: Review 2000 by John R de Laeter et al. Pure Appl. Chem. 2003 (75) 683-800
© IUPAC 2003

CIAAW

Lead
A_r(Pb) = 207.2(1) since 1969
The name derives from the Anglo-Saxon lead, which is of unknown origin. The element was knownfrom prehistoric times. The chemical symbol Pb is derived from the Latin plumbum.

Isotopic reference materials of lead.

IUPAC Commission on Isotopic Abundances and Atomic Weights.

These tables are based on the 2015 table with changes from the 2015 table for the values of aluminium, argon, cobalt, gold, holmium, iridium, manganese, niobium, praseodymium, protactinium, rhodium, terbium, thulium and yttrium. See report 5 June 2018. The revised value of hafnium was reported 11 December 2019

https://www.qmul.ac.uk/sbcs/iupac/AtWt/

World Wide Web version of atomic weight data originally prepared by G. P. Moss, from a file provided by D. R. Lide.

Previous values may be consulted from the 1993 table, the 1995 table, the 1997 table, the 1999 table, the 2001 table, the 2005 table, the 2007 table, the 2009 table, the 2011 table, the 2013 table or the 2015 table.

The standard atomic weights of twelve elements having two or more stable isotopes have variability of atomic-weight values in natural terrestrial materials. These are given in table 1 below. In the other lists the values quoted are those suggested for material where the origin of the sample is unknown. For radioactive elements the isotope with the longest half-life is quoted in parenthesis. The original paper should be consulted for full details of the variation in atomic weight and the half life of the radioisotopes quoted below.

A number in parentheses indicates the uncertainty in the last digit of the atomic weight.

See below for the elements listed in Atomic Number Order or Name order.

See also a copy of the periodic table with atomic weights to five significant figures.

Table 1. List of Elements with Range of Atomic Weights.

At No	Symbol	Name	Minimum Atomic Wt	Maximum Atomic Wt
1	H	hydrogen	1.007 84	1.008 11
3	Li	lithium	6.938	6.997
5	B	boron	10.806	10.821
6	C	carbon	12.0096	12.0116
7	N	nitrogen	14.006 43	14.007 28
8	O	oxygen	15.999 03	15.999 77
12	Mg	magnesium	24.304	24.307
14	Si	silicon	28.084	28.086
16	S	sulfur	32.059	32.076
17	Cl	chlorine	35.446	35.457
18	Ar	argon	39.792	39.963
35	Br	bromine	79.901	79.907
81	Tl	thallium	204.382	204.385

See original paper for the range of these elements from different sources [Isotope-abundance variations and atomic weights of selected elements: 2016 (IUPAC Technical Report), Pure Appl. Chem. 2016, 88(12), 1203-1224.]

Table 2. List of Elements in Atomic Number Order.

At No	Symbol	Name	Atomic Wt	Notes
1	H	Hydrogen	1.008	3, 5
2	He	Helium	4.002 602(2)	1, 2
3	Li	Lithium	6.94	3, 5
4	Be	Beryllium	9.012 1831(5)
5	B	Boron	10.81	3, 5
6	C	Carbon	12.011	5
7	N	Nitrogen	14.007	5
8	O	Oxygen	15.999	5
9	F	Fluorine	18.998 403 163(6)
10	Ne	Neon	20.1797(6)	1, 3
11	Na	Sodium	22.989 769 28(2)
12	Mg	Magnesium	24.305	5
13	Al	Aluminium	26.981 5384(3)
14	Si	Silicon	28.085	5
15	P	Phosphorus	30.973 761 998(5)
16	S	Sulfur	32.06	5
17	Cl	Chlorine	35.45	3, 5
18	Ar	Argon	39.948(1)	1, 2, 5
19	K	Potassium	39.0983(1)
20	Ca	Calcium	40.078(4)
21	Sc	Scandium	44.955 908(5)
22	Ti	Titanium	47.867(1)
23	V	Vanadium	50.9415(1)
24	Cr	Chromium	51.9961(6)
25	Mn	Manganese	54.938 043(2)
26	Fe	Iron	55.845(2)
27	Co	Cobalt	58.933 194(3)
28	Ni	Nickel	58.6934(4)	2
29	Cu	Copper	63.546(3)	2
30	Zn	Zinc	65.38(2)	2
31	Ga	Gallium	69.723(1)
32	Ge	Germanium	72.630(8)
33	As	Arsenic	74.921 595(6)
34	Se	Selenium	78.971(8)
35	Br	Bromine	79.904	5
36	Kr	Krypton	83.798(2)	1, 3
37	Rb	Rubidium	85.4678(3)	1
38	Sr	Strontium	87.62(1)	1, 2
39	Y	Yttrium	88.905 84(1)
40	Zr	Zirconium	91.224(2)	1
41	Nb	Niobium	92.906 37(1)
42	Mo	Molybdenum	95.95(1)	1
43	Tc	Technetium	[97]	4
44	Ru	Ruthenium	101.07(2)	1
45	Rh	Rhodium	102.905 49(2)
46	Pd	Palladium	106.42(1)	1
47	Ag	Silver	107.8682(2)	1
48	Cd	Cadmium	112.414(4)	1
49	In	Indium	114.818(1)
50	Sn	Tin	118.710(7)	1
51	Sb	Antimony	121.760(1)	1
52	Te	Tellurium	127.60(3)	1
53	I	Iodine	126.904 47(3)
54	Xe	Xenon	131.293(6)	1, 3
55	Cs	Caesium	132.905 451 96(6)
56	Ba	Barium	137.327(7)
57	La	Lanthanum	138.905 47(7)	1
58	Ce	Cerium	140.116(1)	1
59	Pr	Praseodymium	140.907 66(1)
60	Nd	Neodymium	144.242(3)	1
61	Pm	Promethium	[145]
62	Sm	Samarium	150.36(2)	1
63	Eu	Europium	151.964(1)	1
64	Gd	Gadolinium	157.25(3)	1
65	Tb	Terbium	158.925 354(8)
66	Dy	Dysprosium	162.500(1)	1
67	Ho	Holmium	164.930 328(7)
68	Er	Erbium	167.259(3)	1
69	Tm	Thulium	168.934 218(6)
70	Yb	Ytterbium	173.045(10)	1
71	Lu	Lutetium	174.9668(1)	1
72	Hf	Hafnium	178.486(6)
73	Ta	Tantalum	180.947 88(2)
74	W	Tungsten	183.84(1)
75	Re	Rhenium	186.207(1)
76	Os	Osmium	190.23(3)	1
77	Ir	Iridium	192.217(2)
78	Pt	Platinum	195.084(9)
79	Au	Gold	196.966 570(4)
80	Hg	Mercury	200.592(3)
81	Tl	Thallium	204.38	5
82	Pb	Lead	207.2(1)	1, 2
83	Bi	Bismuth	208.980 40(1)
84	Po	Polonium	[209]	4
85	At	Astatine	[210]	4
86	Rn	Radon	[222]	4
87	Fr	Francium	[223]	4
88	Ra	Radium	[226]	4
89	Ac	Actinium	[227]	4
90	Th	Thorium	232.0377(4)	1, 4
91	Pa	Protactinium	231.035 88(1)	4
92	U	Uranium	238.028 91(3)	1, 3, 4
93	Np	Neptunium	[237]	4
94	Pu	Plutonium	[244]	4
95	Am	Americium	[243]	4
96	Cm	Curium	[247]	4
97	Bk	Berkelium	[247]	4
98	Cf	Californium	[251]	4
99	Es	Einsteinium	[252]	4
100	Fm	Fermium	[257]	4
101	Md	Mendelevium	[258]	4
102	No	Nobelium	[259]	4
103	Lr	Lawrencium	[262]	4
104	Rf	Rutherfordium	[267]	4
105	Db	Dubnium	[270]	4
106	Sg	Seaborgium	[269]	4
107	Bh	Bohrium	[270]	4
108	Hs	Hassium	[270]	4
109	Mt	Meitnerium	[278]	4
110	Ds	Darmstadtium	[281]	4
111	Rg	Roentgenium	[281]	4
112	Cn	Copernicium	[285]	4
113	Nh	Nihonium	[286]	4
114	Fl	Flerovium	[289]	4
115	Mc	Moscovium	[289]	4
116	Lv	Livermorium	[293]	4
117	Ts	Tennessine	[293]	4
118	Og	Oganesson	[294]	4

1. Geological specimens are known in which the element has an isotopic composition outside the limits for normal material. The difference between the atomic weight of the element in such specimens and that given in the Table may exceed the stated uncertainty.
2. Range in isotopic composition of normal terrestrial material prevents a more precise value being given; the tabulated value should be applicable to any normal material.
3. Modified isotopic compositions may be found in commercially available material because it has been subject to an undisclosed or inadvertant isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the Table can occur.
4. Element has no stable nuclides. The value enclosed in brackets, e.g. [209], indicates the mass number of the longest-lived isotope of the element. However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.
5. See table 1 for details of range and original paper for the atomic weight of the element from different sources.

Table 3. List of Elements in Name Order.

At No	Symbol	Name	Atomic Wt	Notes
89	Ac	Actinium	[227]	4
13	Al	Aluminium	26.981 5384(3)
95	Am	Americium	[243]	4
51	Sb	Antimony	121.760(1)	1
18	Ar	Argon	39.948(1)	1, 2, 5
33	As	Arsenic	74.921 595(6)
85	At	Astatine	[210]	4
56	Ba	Barium	137.327(7)
97	Bk	Berkelium	[247]	4
4	Be	Beryllium	9.012 1831(5)
83	Bi	Bismuth	208.980 40(1)
107	Bh	Bohrium	[270]	4
5	B	Boron	10.81	3, 5
35	Br	Bromine	79.904	5
48	Cd	Cadmium	112.414(4)	1
55	Cs	Caesium	132.905 451 96(6)
20	Ca	Calcium	40.078(4)	1
98	Cf	Californium	[251]	4
6	C	Carbon	12.011	5
58	Ce	Cerium	140.116(1)	1
17	Cl	Chlorine	35.45	3, 5
24	Cr	Chromium	51.9961(6)
27	Co	Cobalt	58.933 194(3)
112	Cn	Copernicium	[285]	4
29	Cu	Copper	63.546(3)	2
96	Cm	Curium	[247]	4
110	Ds	Darmstadtium	[281]	4
105	Db	Dubnium	[270]	4
66	Dy	Dysprosium	162.500(1)	1
99	Es	Einsteinium	[252]	4
68	Er	Erbium	167.259(3)	1
63	Eu	Europium	151.964(1)	1
100	Fm	Fermium	[257]	4
114	Fl	Flerovium	[289]	4
9	F	Fluorine	18.998 403 163(6)
87	Fr	Francium	[223]	4
64	Gd	Gadolinium	157.25(3)	1
31	Ga	Gallium	69.723(1)
32	Ge	Germanium	72.630(8)
79	Au	Gold	196.966 570(4)
72	Hf	Hafnium	178.486(6)
108	Hs	Hassium	[270]	4
2	He	Helium	4.002 602(2)	1, 2
67	Ho	Holmium	164.930 328(7)
1	H	Hydrogen	1.008	3, 5
49	In	Indium	114.818(1)
53	I	Iodine	126.904 47(3)
77	Ir	Iridium	192.217(2)
26	Fe	Iron	55.845(2)
36	Kr	Krypton	83.798(2)	1, 3
57	La	Lanthanum	138.905 47(7)	1
103	Lr	Lawrencium	[262]	4
82	Pb	Lead	207.2(1)	1, 2
3	Li	Lithium	6.94	3, 5
116	Lv	Livermorium	[293]	4
71	Lu	Lutetium	174.9668(1)	1
12	Mg	Magnesium	24.305	5
25	Mn	Manganese	54.938 043(2)
109	Mt	Meitnerium	[278]	4
101	Md	Mendelevium	[258]	4
80	Hg	Mercury	200.592(3)
42	Mo	Molybdenum	95.95(1)	1
115	Mc	Moscovium	[289]	4
60	Nd	Neodymium	144.242(3)	1
10	Ne	Neon	20.1797(6)	1, 3
93	Np	Neptunium	[237]	4
28	Ni	Nickel	58.6934(4)
113	Nh	Nihonium	[286]	4
41	Nb	Niobium	92.906 37(1)
7	N	Nitrogen	14.007	5
102	No	Nobelium	[259]	4
118	Og	Oganesson	[294]	4
76	Os	Osmium	190.23(3)	1
8	O	Oxygen	15.999	5
46	Pd	Palladium	106.42(1)	1
15	P	Phosphorus	30.973 761 998(5)
78	Pt	Platinum	195.084(9)
94	Pu	Plutonium	[244]	4
84	Po	Polonium	[209]	4
19	K	Potassium	39.0983(1)
59	Pr	Praseodymium	140.907 66(1)
61	Pm	Promethium	[145]	4
91	Pa	Protactinium	231.035 88(1)	4
88	Ra	Radium	[226]	4
86	Rn	Radon	[222]	4
75	Re	Rhenium	186.207(1)
45	Rh	Rhodium	102.905 49(2)
111	Rg	Roentgenium	[281]	4
37	Rb	Rubidium	85.4678(3)	1
44	Ru	Ruthenium	101.07(2)	1
104	Rf	Rutherfordium	[267]	4
62	Sm	Samarium	150.36(2)	1
21	Sc	Scandium	44.955 908(5)
106	Sg	Seaborgium	[269]	4
34	Se	Selenium	78.971(8)
14	Si	Silicon	28.085	5
47	Ag	Silver	107.8682(2)	1
11	Na	Sodium	22.989 769 28(2)
38	Sr	Strontium	87.62(1)	1, 2
16	S	Sulfur	32.06	5
73	Ta	Tantalum	180.947 88(2)
43	Tc	Technetium	[97]	4
52	Te	Tellurium	127.60(3)	1
117	Ts	Tennessine	[293]	4
65	Tb	Terbium	158.925 354(8)
81	Tl	Thallium	204.38	5
90	Th	Thorium	232.0377(4)	1, 4
69	Tm	Thulium	168.934 218(6)
50	Sn	Tin	118.710(7)	1
22	Ti	Titanium	47.867(1)
74	W	Tungsten	183.84(1)
92	U	Uranium	238.028 91(3)	1, 3, 4
23	V	Vanadium	50.9415(1)
54	Xe	Xenon	131.293(6)	1, 3
70	Yb	Ytterbium	173.045(10)	1
39	Y	Yttrium	88.905 84(1)
30	Zn	Zinc	65.38(2)	2
40	Zr	Zirconium	91.224(2)	1

1. Geological specimens are known in which the element has an isotopic composition outside the limits for normal material. The difference between the atomic weight of the element in such specimens and that given in the Table may exceed the stated uncertainty.
2. Range in isotopic composition of normal terrestrial material prevents a more precise value being given; the tabulated value should be applicable to any normal material.
3. Modified isotopic compositions may be found in commercially available material because it has been subject to an undisclosed or inadvertant isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the Table can occur.
4. Element has no stable nuclides. The value enclosed in brackets, e.g. [209], indicates the mass number of the longest-lived isotope of the element. However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.
5. See table 1 for details of range and original paper for the atomic weight of the element from different sources.

Atomic Mass And Number Worksheet

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