Periodic table reference

Atomic number, symbol, standard atomic weight, group, period, category and electron configuration for all 118 chemical elements, using the IUPAC 2021 standard atomic weights.

Two of these columns carry a caveat worth knowing. 14 elements have an atomic weight that IUPAC publishes as an interval rather than a single number, because their isotopic composition varies measurably between natural sources — for those, the fourth digit carries real uncertainty. Another 34 have no stable isotope at all, so the figure shown is a mass number, which is an integer count of nucleons rather than a measured average. Each element page says which applies.

Z	Symbol	Element	Atomic weight	Group	Period	Category
1	H	Hydrogen	1.008†	1	1	Reactive nonmetal
2	He	Helium	4.0026	18	1	Noble gas
3	Li	Lithium	6.94†	1	2	Alkali metal
4	Be	Beryllium	9.0122	2	2	Alkaline earth metal
5	B	Boron	10.81†	13	2	Metalloid
6	C	Carbon	12.011†	14	2	Reactive nonmetal
7	N	Nitrogen	14.007†	15	2	Reactive nonmetal
8	O	Oxygen	15.999†	16	2	Reactive nonmetal
9	F	Fluorine	18.998	17	2	Halogen
10	Ne	Neon	20.18	18	2	Noble gas
11	Na	Sodium	22.99	1	3	Alkali metal
12	Mg	Magnesium	24.305†	2	3	Alkaline earth metal
13	Al	Aluminium	26.982	13	3	Post-transition metal
14	Si	Silicon	28.085†	14	3	Metalloid
15	P	Phosphorus	30.974	15	3	Reactive nonmetal
16	S	Sulfur	32.06†	16	3	Reactive nonmetal
17	Cl	Chlorine	35.45†	17	3	Halogen
18	Ar	Argon	39.95†	18	3	Noble gas
19	K	Potassium	39.098	1	4	Alkali metal
20	Ca	Calcium	40.078	2	4	Alkaline earth metal
21	Sc	Scandium	44.956	3	4	Transition metal
22	Ti	Titanium	47.867	4	4	Transition metal
23	V	Vanadium	50.942	5	4	Transition metal
24	Cr	Chromium	51.996	6	4	Transition metal
25	Mn	Manganese	54.938	7	4	Transition metal
26	Fe	Iron	55.845	8	4	Transition metal
27	Co	Cobalt	58.933	9	4	Transition metal
28	Ni	Nickel	58.693	10	4	Transition metal
29	Cu	Copper	63.546	11	4	Transition metal
30	Zn	Zinc	65.38	12	4	Transition metal
31	Ga	Gallium	69.723	13	4	Post-transition metal
32	Ge	Germanium	72.63	14	4	Metalloid
33	As	Arsenic	74.922	15	4	Metalloid
34	Se	Selenium	78.971	16	4	Reactive nonmetal
35	Br	Bromine	79.904†	17	4	Halogen
36	Kr	Krypton	83.798	18	4	Noble gas
37	Rb	Rubidium	85.468	1	5	Alkali metal
38	Sr	Strontium	87.62	2	5	Alkaline earth metal
39	Y	Yttrium	88.906	3	5	Transition metal
40	Zr	Zirconium	91.224	4	5	Transition metal
41	Nb	Niobium	92.906	5	5	Transition metal
42	Mo	Molybdenum	95.95	6	5	Transition metal
43	Tc	Technetium	98*	7	5	Transition metal
44	Ru	Ruthenium	101.07	8	5	Transition metal
45	Rh	Rhodium	102.91	9	5	Transition metal
46	Pd	Palladium	106.42	10	5	Transition metal
47	Ag	Silver	107.87	11	5	Transition metal
48	Cd	Cadmium	112.41	12	5	Transition metal
49	In	Indium	114.82	13	5	Post-transition metal
50	Sn	Tin	118.71	14	5	Post-transition metal
51	Sb	Antimony	121.76	15	5	Metalloid
52	Te	Tellurium	127.6	16	5	Metalloid
53	I	Iodine	126.9	17	5	Halogen
54	Xe	Xenon	131.29	18	5	Noble gas
55	Cs	Caesium	132.91	1	6	Alkali metal
56	Ba	Barium	137.33	2	6	Alkaline earth metal
57	La	Lanthanum	138.91	—	6	Lanthanide
58	Ce	Cerium	140.12	—	6	Lanthanide
59	Pr	Praseodymium	140.91	—	6	Lanthanide
60	Nd	Neodymium	144.24	—	6	Lanthanide
61	Pm	Promethium	145*	—	6	Lanthanide
62	Sm	Samarium	150.36	—	6	Lanthanide
63	Eu	Europium	151.96	—	6	Lanthanide
64	Gd	Gadolinium	157.25	—	6	Lanthanide
65	Tb	Terbium	158.93	—	6	Lanthanide
66	Dy	Dysprosium	162.5	—	6	Lanthanide
67	Ho	Holmium	164.93	—	6	Lanthanide
68	Er	Erbium	167.26	—	6	Lanthanide
69	Tm	Thulium	168.93	—	6	Lanthanide
70	Yb	Ytterbium	173.05	—	6	Lanthanide
71	Lu	Lutetium	174.97	—	6	Lanthanide
72	Hf	Hafnium	178.49	4	6	Transition metal
73	Ta	Tantalum	180.95	5	6	Transition metal
74	W	Tungsten	183.84	6	6	Transition metal
75	Re	Rhenium	186.21	7	6	Transition metal
76	Os	Osmium	190.23	8	6	Transition metal
77	Ir	Iridium	192.22	9	6	Transition metal
78	Pt	Platinum	195.08	10	6	Transition metal
79	Au	Gold	196.97	11	6	Transition metal
80	Hg	Mercury	200.59	12	6	Transition metal
81	Tl	Thallium	204.38†	13	6	Post-transition metal
82	Pb	Lead	207.2†	14	6	Post-transition metal
83	Bi	Bismuth	208.98	15	6	Post-transition metal
84	Po	Polonium	209*	16	6	Post-transition metal
85	At	Astatine	210*	17	6	Halogen
86	Rn	Radon	222*	18	6	Noble gas
87	Fr	Francium	223*	1	7	Alkali metal
88	Ra	Radium	226*	2	7	Alkaline earth metal
89	Ac	Actinium	227*	—	7	Actinide
90	Th	Thorium	232.04	—	7	Actinide
91	Pa	Protactinium	231.04	—	7	Actinide
92	U	Uranium	238.03	—	7	Actinide
93	Np	Neptunium	237*	—	7	Actinide
94	Pu	Plutonium	244*	—	7	Actinide
95	Am	Americium	243*	—	7	Actinide
96	Cm	Curium	247*	—	7	Actinide
97	Bk	Berkelium	247*	—	7	Actinide
98	Cf	Californium	251*	—	7	Actinide
99	Es	Einsteinium	252*	—	7	Actinide
100	Fm	Fermium	257*	—	7	Actinide
101	Md	Mendelevium	258*	—	7	Actinide
102	No	Nobelium	259*	—	7	Actinide
103	Lr	Lawrencium	266*	—	7	Actinide
104	Rf	Rutherfordium	267*	4	7	Transition metal
105	Db	Dubnium	268*	5	7	Transition metal
106	Sg	Seaborgium	269*	6	7	Transition metal
107	Bh	Bohrium	270*	7	7	Transition metal
108	Hs	Hassium	269*	8	7	Transition metal
109	Mt	Meitnerium	278*	9	7	Transition metal
110	Ds	Darmstadtium	281*	10	7	Transition metal
111	Rg	Roentgenium	282*	11	7	Transition metal
112	Cn	Copernicium	285*	12	7	Transition metal
113	Nh	Nihonium	286*	13	7	Post-transition metal
114	Fl	Flerovium	289*	14	7	Post-transition metal
115	Mc	Moscovium	290*	15	7	Post-transition metal
116	Lv	Livermorium	293*	16	7	Post-transition metal
117	Ts	Tennessine	294*	17	7	Halogen
118	Og	Oganesson	294*	18	7	Noble gas

* mass number of the longest-lived isotope, not a measured atomic weight. † IUPAC publishes an interval; the conventional value is shown.

Group, period, category and electron configuration are computed from the atomic number rather than stored, so they cannot fall out of step with it. The lanthanides and actinides show no group because they genuinely have none in the modern IUPAC layout — that is the correct answer, not a gap.