Objective Test - PERIODIC TABLE

Periodic Properties of Elements

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1. The electron configuration of Cl^- is (the Periodic Table should help you):
1. 1s2s²2p⁶3s²3p⁵
2. 1s²2s²2p⁶3s²3p⁶
3. 1s²2s²2p⁶3d¹⁰
4. 1s²2s²2p⁶
5. 1s²2s²2p⁶3s²3p⁶3d¹⁰
2. How many unpaired electrons are present in ground-state atomic nitrogen?
1. 0
2. 2
3. 4
4. 3
5. 5
3. Which orbital is being filled in the lanthanide series?
1. 4f
2. 4d
3. 5f
4. 5d
5. 3p
4. Which of the following elements is not a metal?
1. Na
2. Cu
3. Pb
4. Mg
5. C
5. Which of the following pairs is isoelectronic?
1. Li, Be²⁺
2. F^-, Na⁺
3. O, F^-
4. Li⁺, Na⁺
6. Which of the following has the largest radius?
1. Na⁺
2. Li⁺
3. Cl^-
4. Cl
5. H
7. Which of the following has the largest first electron affinity (ignore sign, just magnitude)?
1. F
2. Li
3. Na
4. Br
5. Ne
8. The electron configuration of S^2- is (the Periodic Table should help you):
1. 1s²2s²2p⁶3s²3p⁵
2. 1s²2s²2p⁶3s²3p⁶
3. 1s²2s²2p⁶3d¹⁰
4. 1s²2s²2p⁶
5. 1s²2s²2p⁶3s²3p⁶3d¹⁰
9. How many unpaired electrons are present in ground-state atomic oxygen?
1. 0
2. 2
3. 4
4. 3
5. 5
10. Which of the following has the largest radius?
1. K
2. K⁺
3. Cl^-
4. Cl
5. Ne
11. Which of the following has the most favorable first electron affinity?
1. F
2. Li
3. Na
4. Br
5. Ne
12. Which of the following has the lowest ionization energy?
1. Li
2. K⁺
3. K
4. Ne
5. O
13. How many unpaired electrons are there in Arsenic (As)?
1. 0
2. 1
3. 2
4. 3
5. 4
14. An element has an electron configuration of 1s²2s²2p⁶3s². Which electrons experience the greatest effective nuclear charge, and which experience the most shielding, respectively?

	greatest effective nuclear charge	most shielding
(a)	1s2 electrons	2s2 electrons
(b)	1s2 electrons	3s2 electrons
(c)	2s2 electrons	3s2 electrons
(d)	3s2 electrons	1s2 electrons
(e)	3s2 electrons	2p6 electrons

15. Choose the electron configuration that results when the outermost electron is ionized from the Se atom.
1. [Ar]4s²3d¹⁰4p⁴
2. [Ar]4s²3d¹⁰4p³
3. [Ar]4s²3d¹⁰4p⁵
4. [Ar]4s¹3d¹⁰4p³
5. none of the above are correct
16. Which of the following has the highest electron affinity?
1. Cs
2. Na
3. Si
4. Ne
5. F
17. Which of the following has the largest first ionization energy?
1. Cs
2. Na
3. Si
4. Ne
5. F
18. Which of the following elements has the most nonmetallic character?
1. F
2. Ge
3. Hg
4. In
5. S
19. What is the electron configuration of Fe³⁺?
1. [Ar]4s²3d⁹
2. [Ar]4s¹3d⁵
3. [Ar]4s²3d³
4. [Ar]3d⁵
5. [Ar]3d⁶
20. Which of the following elements is the least electronegative?
1. F
2. Ga
3. Os
4. P
5. Ra
21. Which of the following has the largest size?
1. O
2. F
3. Al³⁺
4. K⁺
5. Rb
22. Which of the following is the correct electron configuration for Ge atoms in the ground state?
1. [Ne]4s²3d¹⁰
2. [Ne]4s²3d¹⁰4p¹
3. [Kr]4s²3d¹⁰4p³
4. [Ar]4s²3d¹⁰4p²
5. [Ar]4s²3d¹⁰4p⁴
23. Which of the following sets is isoelectronic with Xe?
1. I^-, Cs⁺, Ba²⁺, La³⁺
2. Br^-, I^-, Cs, Cs⁺
3. He, Ne, Ar, Kr
4. Sn²⁺, Sb³⁺, Te^2-, I^-
5. Sn⁴⁺, Sb⁵⁺, Te^2- , I
24. All the following diagrams represent an atom in the ground state EXCEPT:

25. Which of the following neutral atoms would be the smallest?
1. Cs
2. Li
3. Rb
4. K
5. Na
26. Identify the element in the second period (row) whose first six successive ionization energies in units of electron volts are listed below:

IE1	IE2	IE3	IE4	IE5	IE6
11	24	48	64	392	490

1. Boron
2. Carbon
3. Nitrogen
4. Oxygen
5. Fluorine
26. For the following atoms the order of increasing electron affinity is:
1. Br < Rb < Cl < I
2. I < Rb < Cl < Br
3. Rb < I < Br < Cl
4. Cl < Br < Rb < I
5. Br < Cl < I < Rb
27. Which of the following atoms will have the highest second ionization energy?
1. Na
2. Mg
3. Al
4. Ca
5. Y
28. Which pair of elements react to form an ionic compound?
1. calcium and copper
2. calcium and chlorine
3. nitrogen and chlorine
4. argon and oxygen
5. fluorine and iodine
29. The smallest atom in the following list is:
1. B
2. C
3. N
4. P
5. As
30. Which of the following elements would be expected to lose electrons and form positive ions when it reacts?
1. phosphorus
2. nitrogen
3. iron
4. iodine
5. fluorine
31. The ion correctly matched with its grounded state electron configuration is:
1. Al³⁺: [Ne]3s²3p⁶
2. Cr³⁺: [Ar]4s²3d¹
3. Fe³⁺: [Ar]3d⁶
4. Zn²⁺: [Ar]4s²3d⁸
5. Ni²⁺: [Ar]3d⁸
32. Arrange the following elements in order of increasing metallic character: As, P, Bi, Sb, N.
1. As, P, Bi, Sb, N
2. N, Sb, Bi, P, As
3. As, Bi, N, P, Sb
4. Bi, Sb, As, P, N
5. N, P, As, Sb, Bi
33. The number of valence electrons in an oxalate ion, C₂O₄^2-, is:
1. 2
2. 10
3. 32
4. 34
5. 44
34. Which of the following oxides is most acidic?
1. Cl₂O₇
2. Al₂O₃
3. Ga₂O₃
4. CaO
5. K₂O
35. Which of the following dissolves in water to form a basic solution?
1. CaO
2. HCl
3. N₂O₅
4. CaO and HCl
5. HCl and N₂O₅
36. Which of the ions is unlikely to be formed?
1. O^2-
2. Al³⁺
3. Na⁺
4. S^3-
5. Mg²⁺
37. The oxidation number of Cr in dichromate ion, Cr₂O₇^2-, is:
1. +3
2. +6
3. +7
4. +12
5. +14
38. Which equation represents an oxidation-reduction reaction?
1. 2HCl(aq) + Mg(s) --> MgCl₂(aq) + H₂(g)
2. Na₂O(s) + H₂O(l) --> 2NaOH(aq)
3. CO₂(g) + H₂O(l) --> H₂CO₃(aq)
4. CaO(s) + SO₃(g) --> CaSO₄(s)
5. NH₃(g) + HCl(g) --> NH₄Cl(s)
39. Which electron configuration for nitrogen would satisfy Hund's Rule?
1. 1s²2s²2p_x¹2p_y¹2p_z¹
2. 1s¹2s¹2p_x¹2p_y¹2p_z¹
3. 1s²2s¹2p_x¹2p_y¹2p_z¹
4. 1s²2s²2p_x³2p_y⁰2p_z⁰
5. 1s²2s²2p_x²2p_y¹2p_z⁰
40. The electron configuration of a certain element is [X]4s²3d¹⁰4p², where X stands for a noble gas. The element in question and the noble gas X are, respectively:
1. Ga and Ar
2. Ge and Ar
3. Sn and Kr
4. Ge and Kr
5. Si and Ar
41. Which of the species below has the electronic configuration 1s²2s²2p⁶?
1. Na⁺
2. O^2-
3. Ne
4. N^3-
5. All of the above
42. Which of the following species has the largest size?
1. S
2. Se
3. Se^2-
4. O^2-
5. F
43. The successive ionization energies of a certain element in units of kJ/mol are: I₁ = 578; I₂ = 1820; I₃ = 2750; I₄ = 11,600. [I₁ is the first ionization energy; I₂, the second, etc.] This element most likely is:
1. Na
2. Mg
3. Al
4. Si
5. P
44. Which of the following elements has the most negative electron affinity?
1. K
2. He
3. Co
4. S
5. Cl
45. From its position in the Periodic Table, the most stable ion of the Z=88 element radium is likely to be:
1. Ra⁺
2. Ra²⁺
3. Ra³⁺
4. Ra^2-
5. Ra^-
46. Lithium is a reactive metal. Which of the following is not a common reaction of Li?
1. 3Li + Al --> Li₃Al
2. 4Li + O₂ --> 2Li₂O
3. 2Li + Cl₂ --> 2LiCl
4. 2Li + 2H₂O --> 2LiOH + H₂
5. All of the reactions (a)-(d) are common reactions.
47. Which of the following are not all isoelectronic?
1. Se^2-, Sr²⁺, Br^-, Rb⁺
2. S^2-, Cl^-, Li⁺, Be²⁺
3. N^3-, O^2-, F^-, Ne
4. Ar, K⁺, Ca²⁺, Sc³⁺
5. Te^2-, I^-, Cs⁺, Ba²⁺
48. What are the changes in oxidation numbers in the reaction:

MnO₂(s) + 4HCl(aq) --> MnCl₂(aq) + Cl₂(aq) + 2H₂O(l)

1. Cl increases from -1 to 0; Mn decreases from +4 to +2.
2. H increases from -1 to +1; Mn decreases from +4 to +2.
3. H increases from -1 to +1; O decreases from -1 to -2.
4. Mn increases from +2 to +4; O decreases from -1 to -2.
5. There are no changes in oxidation number.
49. Which of the following reactions is not an oxidation-reduction reaction?
1. 2Cs + Cl₂ --> 2CsCl
2. N₂ + 3H₂ --> 2NH₃
3. SO₃ + H₂O --> H₂SO₄
4. Cu + 2Ag⁺ --> Cu²⁺ + 2Ag
5. 2K + 2H₂O --> 2KOH + H₂
50. What is the correct electron configuration for C?
1. 1s²2s²
2. 1s²2s²3p⁴
3. 1s¹2s²
4. 1s²2s²2p²
5. 1s²2s²2p⁶3s²
51. The second row transition-metal period involves filling which sub-shell?
1. 4d
2. 3f
3. 3d
4. 2d
5. 3p
52. Which one of the following elements is not a metal?
1. Sn
2. Na
3. Fe
4. S
5. Be
53. Which one of the following statements is incorrect?
1. The radius of Na is larger than Na⁺
2. The radius of Mg is larger than Na
3. The ionization energy of Na is smaller than Na⁺
4. The electron affinity of Cl is more negative than C (carbon)
54. Which of the following atoms has the smallest radius?
1. Na
2. K
3. Al
4. Kr
5. Ar
55. Which of the elements below has the smallest first ionization energy?
1. F
2. Mg
3. Kr
4. K
5. Li
56. Identify the element having the first three ionization energies as follows: I₁ = 900 kJ/mol; I₂ = 1760 kJ/mol; I₃ = 14,900 kJ/mol
1. H
2. He
3. Li
4. Be
5. B
57. Which of the following elements is X in the compound LiXO₃?
1. Mg
2. Al
3. C
4. N
5. Ne
58. Which of the following is least metallic?
1. As
2. Ge
3. Ga
4. In
5. Tl
59. Cr has the electronic configuration [Ar]4s²3d^x. How many d electrons are in a Cr atom?
1. 2
2. 4
3. 5
4. 6
5. 8
60. The electron affinity of F is, in effect, the energy required for which of the following reactions?
1. F₂(g) --> 2F(g)
2. F(g) --> F⁺(g) + e^-
3. F⁺(g) --> F₂⁺(g) + e^-
4. F^-(g) --> F(g) + e^-
5. F₂(g) + e^- --> F^-(g) + F(g)
61. Which of the following compounds is LEAST likely to exist?
1. BaF₂
2. LaF₃
3. SrF₃
4. PbS
5. Ca(OH)₂
62. Which of the following atoms can form an oxide involving the highest oxidation state?
1. Li
2. N
3. K
4. Ga
5. Ba
63. The oxidation number of iodine in KIO₄ is:
1. +7
2. +5
3. +3
4. +1
5. -1
64. The vertical columns in the Periodic Table are commonly referred to as:
1. groups.
2. families.
3. periods.
4. verticals.
5. categories.
65. Given that the electronic structure of the nitrogen atom is 1s²2s²2p³, how many unpaired electrons are present in atomic oxygen?
1. 2
2. 4
3. 3
4. 8
5. 1
66. Which of the following is an alkali metal?
1. H
2. Ca
3. Zn
4. Fe
5. Rb
67. The electron configuration of ₁₃Al³⁺ is:
1. 1s²2s²2p⁶3s²3p¹
2. 1s²2s²2p⁶3s²
3. 1s²2s²2p⁶
4. 1s²2s²2p³3s²3p¹
5. 1s²2s²2p⁶3d³
68. Which of the following ions does not have the electronic configuration of argon, ₁₈Ar?
1. ₁₇Cl^-
2. ₁₉K⁺
3. ₂₀Ca²⁺
4. ₂₁Sc³⁺
5. ₉F^-
69. Which of the following statements are incorrect?
1. Atoms tend to get larger as one goes across the Periodic Table from left to right in a given period.
2. Atoms get larger as one proceeds down a given group.
3. For a given pair of isoelectronic ions, cations are smaller than anions.
4. The first ionization energy for a given element tends to be smaller than the second ionization energy.
5. Less electronegative elements tend to have smaller ionization energies.
70. The ability of an element to act as an oxidizing agent tends to:
1. increase as the ionization energy decreases.
2. increase as the electronegativity increases.
3. increase as the atom becomes larger.
4. increase as the element becomes more metallic.
5. decrease as the electronegativity increases.
71. The electron configuration of phosphorus is:
1. [He]2s²3p³
2. [Ne]3s²3p³
3. [Ne]3s²3p⁴
4. [Ne]3s²3d¹⁰3p³
5. none of these
72. Which of the following pairs is isoelectronic?
1. F, Cl
2. K, Cl
3. Li⁺, H
4. H^-, He
5. Ne, Ar
73. Given that the electronic structure of oxygen is [He]2s²2p⁴, how many unpaired electrons are there in O^2-?
1. 8
2. 2
3. 4
4. 10
5. 0
74. Which of the following statements is incorrect?
1. Atoms get larger as one moves down a group in the Periodic Table.
2. Atoms get larger as one moves to the right across a period in the Periodic Table.
3. Atoms get smaller when electrons are removed.
4. Ne atoms are smaller than Na atoms.
75. Which of the following statements is correct?
1. Ionization energies get smaller as more electrons are removed from an atom.
2. The ionization energy increases as one moves down a group.
3. The ionization energy increases as one moves to the right across a period.
4. Electron affinities are always larger than ionization energies.
5. None of the above.
76. Which of the following salts has the largest lattice energy?
1. MgO
2. CH₄
3. Na₂O
4. NaI
5. CO₂
77. Which one of the following sets are all metals?
1. Mg, Li, C
2. H, Li, Na
3. He, Be, Mg
4. Al, Si, P
5. Ca, Cr, Co
78. Which of the following is covalent?
1. Li₂S
2. MgO
3. Fe₂O₃
4. Bi₂O₃
5. P₂O₅
79. What is the oxidation number of phosphorus in H₂PO₄^-?
1. +3
2. +4
3. +5
4. +6
5. +7
80. Which of the following increase as you proceed down a group on the periodic table?
1. atomic radius
2. ionization energy
3. electron affinity
4. electronegativity
5. all of the above

ANSWERS WILL BE PROVIDED LATER

Atomic Structure Worksheet

Atomic Structure Worksheet

Fill in the blanks for the elements in this chart.  For the purposes of this chart, round all atomic masses to the nearest whole number.

Element	Number of Protons	Number of Neutrons	Number of Electrons	Atomic Mass	Atomic Number
lithium
carbon
chlorine
silver
lead
calcium
tantalum
radium
samarium
uranium
americium
lawrencium

Elements of the Periodic Table

(Elements Sorted by Atomic Number)

At. No.	Name	Symbol	At. wt.	Group	Discovery	Discovered By
1	Hydrogen	H	1.0079	Nonmetals	1766	Henry Cavendish
2	Helium	He	4.0026	Noble gases	1868	Pierre Janssen
3	Lithium	Li	6.941	Alkali metals	1817	Johan Arfwedson
4	Beryllium	Be	9.0122	Alkaline earth metals	1798	Louis-Nicolas Vauquelin (isolated by Friedrich Wöhler and Antoine-Alexandre-Brutus Bussy 1828)
5	Boron	B	10.81	Nonmetals	1808	Humphry Davy, and independently by Joseph Gay-Lussac and Louis-Jacques Thénard
6	Carbon	C	12.011	Nonmetals	prehistoric	Unknown
7	Nitrogen	N	14.0067	Nonmetals	1772	Daniel Rutherford
8	Oxygen	O	15.9994	Nonmetals	1774	Joseph Priestley and Karl Scheele, independently of each other
9	Fluorine	F	18.9984	Halogens	1771	Karl Scheele (isolated by Henri Moissan 1886)
10	Neon	Ne	20.1798	Noble gases	1898	William Ramsay and Morris Travers
11	Sodium	Na	22.9898	Alkali metals	1807	Humphry Davy
12	Magnesium	Mg	24.3051	Alkaline earth metals	1755	Joseph Black (oxide isolated by Humphry Davy 1808; pure form isolated by Antoine-Alexandre-Brutus Bussy 1828)
13	Aluminum	Al	26.9815	Other metals	1824	Hans Oersted (also attributed to Friedrich Wöhler 1827)
14	Silicon	Si	28.0855	Nonmetals	1823	Johan Arfwedson
15	Phosphorus	P	30.9738	Nonmetals	1674	Hennig Brand
16	Sulfur	S	32.067	Nonmetals	prehistoric	Unknown
17	Chlorine	Cl	35.4528	Halogens	1774	Karl Scheele
18	Argon	Ar	39.948	Noble gases	1894	John Rayleigh and William Ramsay
19	Potassium	K	39.0983	Alkali metals	1807	Humphry Davy
20	Calcium	Ca	40.078	Alkaline earth metals	1808	Humphry Davy
21	Scandium	Sc	44.9559	Transition metals	1876	Lars Nilson
22	Titanium	Ti	47.867	Transition metals	1790	William Gregor
23	Vanadium	V	50.9415	Transition metals	1801	Andrés del Rio (disputed), or Nils Sefström 1830
24	Chromium	Cr	51.9962	Transition metals	1797	Louis-Nicolas Vauquelin
25	Manganese	Mn	54.938	Transition metals	1774	Johann Gottlieb Gahn
26	Iron	Fe	55.845	Transition metals	prehistoric	Unknown
27	Cobalt	Co	58.9332	Transition metals	1730	Georg Brandt
28	Nickel	Ni	58.6934	Transition metals	1751	Axel Cronstedt
29	Copper	Cu	63.546	Transition metals	prehistoric	Unknown
30	Zinc	Zn	65.409	Transition metals	prehistoric	Unknown
31	Gallium	Ga	69.723	Other metals	1875	Paul Lecoq de Boisbaudran
32	Germanium	Ge	72.61	Other metals	1886	Clemens Winkler
33	Arsenic	As	74.9216	Nonmetals	prehistoric	Unknown
34	Selenium	Se	78.96	Nonmetals	1817	Jöns Berzelius
35	Bromine	Br	79.904	Halogens	1826	Antoine-Jérôme Balard
36	Krypton	Kr	83.798	Noble gases	1898	William Ramsay and Morris Travers
37	Rubidium	Rb	85.4678	Alkali metals	1861	Robert Bunsen and Gustav Kirchhoff
38	Strontium	Sr	87.62	Alkaline earth metals	1808	Humphry Davy
39	Yttrium	Y	88.906	Transition metals	1794	Johan Gadolin
40	Zirconium	Zr	91.224	Transition metals	1789	Martin Klaproth
41	Niobium	Nb	92.9064	Transition metals	1801	Charles Hatchett
42	Molybdenum	Mo	95.94	Transition metals	1781	named by Karl Scheele (isolated by Peter Jacob Hjelm 1782)
43	Technetium	Tc	(98)	Transition metals	1937	Carlo Perrier and Emilio Segrè
44	Ruthenium	Ru	101.07	Transition metals	1827	G. W. Osann (isolated by Karl Klaus 1844)
45	Rhodium	Rh	102.9055	Transition metals	1804	William Wollaston
46	Palladium	Pd	106.42	Transition metals	1804	William Wollaston
47	Silver	Ag	107.8682	Transition metals	prehistoric	Unknown
48	Cadmium	Cd	112.412	Transition metals	1817	Friedrich Strohmeyer
49	Indium	In	114.818	Other metals	1863	Ferdinand Reich and Hieronymus Richter
50	Tin	Sn	118.711	Other metals	prehistoric	Unknown
51	Antimony	Sb	121.760	Other metals	prehistoric	Unknown
52	Tellurium	Te	127.60	Nonmetals	1782	Franz Müller
53	Iodine	I	126.9045	Halogens	1811	Bernard Courtois
54	Xenon	Xe	131.29	Noble gases	1898	William Ramsay and Morris Travers
55	Cesium	Cs	132.9054	Alkali metals	1860	Robert Bunsen and Gustav Kirchhoff
56	Barium	Ba	137.328	Alkaline earth metals	1808	Humphry Davy
57	Lanthanum	La	138.9055	Lanthanide series	1839	Carl Mosander
58	Cerium	Ce	140.115	Lanthanide series	1804	Jöns Berzelius and Wilhelm Hisinger, and independently by Martin Klaproth
59	Praseodymium	Pr	140.908	Lanthanide series	1885	Carl von Welsbach
60	Neodymium	Nd	144.24	Lanthanide series	1885	Carl von Welsbach
61	Promethium	Pm	(145)	Lanthanide series	1945	J. A. Marinsky, Lawrence Glendenin, and Charles Coryell
62	Samarium	Sm	150.36	Lanthanide series	1879	Paul Lecoq de Boisbaudran
63	Europium	Eu	151.966	Lanthanide series	1901	Eugène Demarçay
64	Gadolinium	Gd	157.25	Lanthanide series	1886	Paul Lecoq de Boisbaudran
65	Terbium	Tb	158.9253	Lanthanide series	1843	Carl Mosander
66	Dysprosium	Dy	162.500	Lanthanide series	1886	Paul Lecoq de Boisbaudran
67	Holmium	Ho	164.9303	Lanthanide series	1879	Per Cleve
68	Erbium	Er	167.26	Lanthanide series	1843	Carl Mosander
69	Thulium	Tm	168.9342	Lanthanide series	1879	Per Cleve
70	Ytterbium	Yb	173.04	Lanthanide series	1878	Jean Charles de Marignac
71	Lutetium	Lu	174.967	Transition metals	1907	Georges Urbain and Carl von Welsbach, independently of each other
72	Hafnium	Hf	178.49	Transition metals	1913	Dirk Coster and Georg von Hevesy
73	Tantalum	Ta	180.948	Transition metals	1802	Anders Ekeberg
74	Tungsten	W	183.84	Transition metals	1783	isolated by Juan José Elhuyar and Fausto Elhuyar
75	Rhenium	Re	186.207	Transition metals	1925	Walter Noddack, Ida Tacke, and Otto Berg
76	Osmium	Os	190.23	Transition metals	1804	Smithson Tennant
77	Iridium	Ir	192.217	Transition metals	1804	Smithson Tennant
78	Platinum	Pt	195.08	Transition metals	1557	Julius Scaliger
79	Gold	Au	196.9665	Transition metals	prehistoric	Unknown
80	Mercury	Hg	200.59	Transition metals	prehistoric	Unknown
81	Thallium	Tl	204.3833	Other metals	1861	William Crookes (isolated by William Crookes and Claude August Lamy, independently of each other, in 1862)
82	Lead	Pb	207.2	Other metals	prehistoric	Unknown
83	Bismuth	Bi	208.9804	Other metals	prehistoric	Unknown
84	Polonium	Po	(209)	Other metals	1898	Marie and Pierre Curie
85	Astatine	At	(210)	Halogens	1940	Dale R. Corson, K. R. MacKenzie, and Emilio Segrè
86	Radon	Rn	(222)	Noble gases	1900	Friedrich Dorn
87	Francium	Fr	(223)	Alkali metals	1939	Marguérite Perey
88	Radium	Ra	(226)	Alkaline earth metals	1898	Marie Curie
89	Actinium	Ac	(227)	Actinide series	1899	André Debierne
90	Thorium	Th	232.0381	Actinide series	1828	Jöns Berzelius
91	Protactinium	Pa	231.036	Actinide series	1913	Kasimir Fajans and O. Göhring
92	Uranium	U	238.0289	Actinide series	1789	Martin Klaproth (isolated by Eugène Péligot 1841)
93	Neptunium	Np	(237)	Actinide series	1940	Edwin McMillan and Philip Abelson
94	Plutonium	Pu	(244)	Actinide series	1940	Glenn Seaborg, Edwin McMillan, Joseph Kennedy, and Arthur Wahl
95	Americium	Am	243	Actinide series	1944	Glenn Seaborg, Ralph James, Leon Morgan, and Albert Ghiorso
96	Curium	Cm	(247)	Actinide series	1944	Glenn Seaborg, Ralph James, and Albert Ghiorso
97	Berkelium	Bk	(247)	Actinide series	1949	Glenn Seaborg, Stanley Thompson, and Albert Ghiorso
98	Californium	Cf	(251)	Actinide series	1950	Glenn Seaborg, Stanley Thompson, Kenneth Street, Jr., and Albert Ghiorso
99	Einsteinium	Es	(252)	Actinide series	1952	Albert Ghiorso and coworkers
100	Fermium	Fm	(257)	Actinide series	1955	Albert Ghiorso and coworkers
101	Mendelevium	Md	(258)	Actinide series	1955	Albert Ghiorso, Bernard G. Harvey, Gregory Choppin, Stanley Thompson, and Glenn Seaborg
102	Nobelium	No	(259)	Actinide series	1958	Albert Ghiorso, Torbjørn Sikkeland, J. R. Walton, and Glenn Seaborg
103	Lawrencium	Lr	(260)	Transition metals	1961	Albert Ghiorso, Torbjørn Sikkeland, Almon Larsh, and Robert Latimer
104	Rutherfordium	Rf	(261)	Transition metals	1969	claimed by U.S. scientist Albert Ghiorso and coworkers (disputed by Soviet workers)
105	Dubnium	Db	(262)	Transition metals	1970	claimed by Albert Ghiorso and coworkers (disputed by Soviet workers)
106	Seaborgium	Sg	(266)	Transition metals	1974	claimed by Georgii Flerov and coworkers, and independently by Albert Ghiorso and coworkers
107	Bohrium	Bh	(262)	Transition metals	1976	Georgii Flerov and Yuri Oganessian (confirmed by German scientist Peter Armbruster and coworkers)
108	Hassium	Hs	(263)	Transition metals	1984	Peter Armbruster and coworkers
109	Meitnerium	Mt	(268)	Transition metals	1982	Peter Armbruster and coworkers
110	Darmstadtium	Ds	(271)	Transition metals	1994	Team at the Heavy-Ion Research Laboratory, Darmstadt, Germany
111	Roentgenium	Rg	(272)	Transition metals	1994	Team at the Heavy-Ion Research Laboratory, Darmstadt, Germany
112	Ununbium	Uub	(277)	Transition metals	1996	Team at the Heavy-Ion Research Laboratory, Darmstadt, Germany
114	Ununquadium	Uuq	(285)	Other metals	1998	Team at the Joint Institute for Nuclear Research, Dubna, Russia
116	Ununhexium	Uuh	(292)	Other metals	2000	Team at the Joint Institute for Nuclear Research, Dubna, Russia

By

MANOJ SINGH

Oriental Study Centre