Ionization Energies of Gaseous Atoms (kJ/mol)

Atomic #		1	2	3	4
1	H	1,312
2	He	2,372	5,251
3	Li	520.3	7,298	11,815
4	Be	899.5	1,757	14,849	21,007
5	B	800.7	2,427	3,660	25,026
6	C	1,086	2,353	4,621	6,223
7	N	1,402	2,856	7,475	9,445
8	O	1,314	3,388	5,301	7,469
9	F	1,681	3,374	6,051	8,408
10	Ne	2,081	3,952	6,122	9,370
11	Na	495.9	4,563	6,913	9,544
12	Mg	737.8	1,451	7,733	10,541
13	Al	577.6	1,817	2,745	11,578
14	Si	786.5	1,577	3,232	4,356
15	P	1,012	1,903	2,912	4,957
16	S	999.6	2,251	3,361	4,564
17	Cl	1,251	2,297	3,822	5,158
18	Ar	1,521	2,666	3,931	5,771
19	K	418.9	3,051	4,412	5,877
20	Ca	589.8	1,145	4,912	6,474
21	Sc	631	1,235	2,389	7,089
22	Ti	658	1,310	2,653	4,175
23	V	650	1,414	2,828	4,507
24	Cr	652.9	1,592	2,987	4,740
25	Mn	717.4	1,509	3,249	4,940
26	Fe	759.4	1,561	2,958	5,290
27	Co	758	1,646	3,232	4,950
28	Ni	736.7	1,753	3,394	5,300
29	Cu	745.5	1,958	3,554	5,330
30	Zn	906.4	1,733	3,833	5,730
31	Ga	578.8	1,979	2,963	6,200
32	Ge	762.2	1,537	3,302	4,411
33	As	947	1,798	2,736	4,837
34	Se	941	2,045	2,974	4,144
35	Br	1,140	2,100	3,500	4,560
36	Kr	1,351	2,368	3,565	5,070
37	Rb	403	2,632	3,900	5,080
38	Sr	549.5	1,064	4,210	5,500
39	Y	616	1,181	1,980	5,960
40	Zr	660	1,267	2,218	3,313
41	Nb	664	1,382	2,416	3,700
42	Mo	685	1,558	2,621	4,480
43	Tc	702	1,472	2,850
44	Ru	711	1,617	2,747
45	Rh	720	1,745	2,997
46	Pd	805	1,875	3,177
47	Ag	731	2,074	3,361
48	Cd	867.7	1,631	3,616
49	In	558.3	1,821	2,705	5,200
50	Sn	708.6	1,412	2,943	3,930
51	Sb	833.8	1,595	2,440	4,260

Atomic #		1	2	3	4
52	Te	869.3	1,790	2,698	3,610
53	I	1,008	1,846	3,200
54	Xe	1,170	2,047	3,100
55	Cs	375.7	2,420
56	Ba	502.9	965.3
57	La	538.1	1,067	1,850	4,820
58	Ce	527.4	1,047	1,949	3,547
59	Pr	523.2	1,018	2,086	3,761
60	Nd	529.6	1,035	2,130	3,899
61	Pm	535.9	1,052	2,150	3,970
62	Sm	543.3	1,068	2,260	3,990
63	Eu	546.7	1,085	2,405	4,110
64	Gd	592.6	1,167	1,991	4,250
65	Tb	564.7	1,112	2,114	3,839
66	Dy	571.9	1,126	2,200	4,001
67	Ho	580.7	1,139	2,204	4,100
68	Er	588.7	1,151	2,194	4,115
69	Tm	596.7	1,163	2,544	4,119
70	Yb	603.4	1,176	2,415	4,220
71	Lu	523.6	1,340	2,022	4,360
72	Hf	680	1,440	2,250	3,215
73	Ta	761
74	W	770
75	Re	760
76	Os	840
77	Ir	880
78	Pt	870	1,791
79	Au	890.1	1,980
80	Hg	1,007	1,810	3,300
81	Tl	589.4	1,971	2,878
82	Pb	715.6	1,450	3,082	4,083
83	Bi	703.3	1,610	2,466	4,370
84	Po	812
85	At	890
86	Rn	1,037
87	Fr	384
88	Ra	509.4	971.9
89	Ac	499
90	Th	587
91	Pa	568
92	U	584
93	Np	597
94	Pu	585
95	Am	578
96	Cm	581
97	Bk	601
98	Cf	608
99	Es	619
100	Fm	627
101	Md	635
102	No	642

Reference: Dasent, pps. 44-47; C.E. Moore, "National Standard Reference Data Series," National Bureau of Standards, No. 34, Washington, DC, 1970; W.C. Martin, L. Hagan, J. Reader, and J. Sugar, J. Phys. Chem. Ref. Data, 3, 771-9 (1974)

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Ionization Energies of Gaseous Atoms (kJ/mol)