Chemistry of the Heaviest Elements

Yuichiro Nagame1,2

1Advanced Science Research Center, JAEA 2Graduate School of Science & Engineering, Ibaraki Univ.

6th Asian-Pacific Symposium on

Radiochemistry

September 17-22, 2017, Jeju Island, Korea

JAEA Tokai

2

1 18

1 2

2 13 14 15 16 17

3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18

3 4 5 6 7 8 9 10 11 12

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118

57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

89 90 91 92 93 94 95 96 97 98 99 100 101 102 103

Es FmPa U Np MdPu

Sm GdCe Tm

No LrAm BkCm CfAc ThActinides

YbLa Pr Nd PmLanthanides

DsHsDb Sg BhFr Ra Ac Rf

PdRh

Lu

Mt

Tb Dy Ho ErEu

Rg Lv

Os Ir Pt Au

Nh McCn Fl

Re RnHg Tl Pb Bi AtPoCs Ba La

MoNbZrY

Ta WHf

As

Sr

Br Kr

Rb XeITeSbSn

V

Cd

Mn Fe Co Ge

InRuTc Ag

He

Be B NeF

Se

NC

Cl ArP

Cr

H

Li

Na Mg

K Ca Sc Ti

S

O

Ts Og

Al

Ni Cu Zn Ga

Si

Transuranium elements : Z ≥ 93

Transactinide elements: Z ≥ 104

The heaviest elements: The elements with Z ≥ 101 that are produced only

in heavy-ion-induced nuclear reactions.

The heaviest elements

one atom-at-a-time

3

Naming four new elements

nihonium and symbol Nh, for the element 113

moscovium and symbol Mc, for the element 115

tennessine and symbol Ts, for the element 117

oganesson and symbol Og, for the element 118

Talk by S. Dmitriev (IA-508)

4

Searching for and producing new elements and their chemical / physical

(nuclear) characterization are very challenging subjects in recent advanced

nuclear & radiochemistry.

• How many chemical elements may be synthesized on earth?

• How can they be produced?

• How long can they survive?

• Which properties do determine their stability?

• What are their chemical and physical properties?

• How are the orbital electron configurations affected in the strong

electric field of heavy atoms?

These are the most fundamental questions in science.

Impact on science

Yu. Ts. Oganessian & K. P. Rykaczewski,

Phys. Today, August 2015, p. 32

5

Contents

1. Introduction:

Chemical studies of the heaviest elements

▶ Atom-at-a-time chemistry

▶ Relativistic effects on electronic structure

2. Recent highlighted studies of liquid-phase chemistry

2-1. Complex formation of 104Rf

2-2. Electrochemistry of 101Md & 102No

3. Atomic properties of the heaviest actinides

3-1. Ionization energy of 103Lr

4. Summary & perspectives

JAEA Tandem Accelerator

6

1. Introduction

Objectives:

Chemical studies of the heaviest elements provide crucial & challenging

opportunities

▶ to advance our understanding of properties of matter at the limits of

existence

▶ to elucidate the influence of relativistic effects on atomic electrons

▶ to architect the Periodic Table at the farthest reach

The heaviest elements (Z > 100):

▶ available in quantities of only a few atoms or often one atom-at-a-time

Chemical characterization with an atom-at-a-time scale:

⇒ Extreme Chemistry

7

1. Introduction

Chemical properties:

▶ complex formation abilities

▶ oxidation states & redox potentials

▶ valence electronic states, etc.

⇒ role of relativistic effects on valence electronic structure

of heavy atoms

1. Relativistic effects

2. Atom-at-a-time chemistry

8

Relativistic effects (1)

General: relativity - increase of the mass with increasing velocity

At heavy elements: Increasing nuclear charge plays as the “accelerator”

of the velocity of electrons.

Electrons near the nucleus are attracted closer to the nucleus and move

there with high velocity.

mass increase of the inner electrons and the contraction of the inner

electron orbitals (Bohr radius)

1. Direct relativistic effects

9

Electrons further away from the nucleus are better screened from the

nuclear charge by the inner electrons, and consequently the orbitals of

the outer electrons expand.

2. Indirect relativistic effects

3. Spin-orbit (SO) splitting of levels with l > 0 into two levels with

j = l ± 1/2

It is expected that the heaviest elements would show a drastic

rearrangement of electrons in their atomic ground states, and as the

electron configuration is responsible for the chemical behavior of elements,

such relativistic effects can lead to surprising chemical properties.

Increasing deviations from the periodicity of chemical properties

based on extrapolation from lighter homologues in the Periodic Table

are predicted.

Relativistic effects (2)

10

Cracks in the Periodic Table

E. Scerri, Scientific American, June 2013, p. 68

…..table may be losing its power due to relativistic effects.

11

Typical production rates of the heaviest

nuclides used for chemical studies

Z Nuclide T1/2 Reaction σ / nb Production

rate*

101 255Md 27 min 248Cm(11B, 4n) 4000 1380 min-1

102 255No 3.5 min 248Cm(12C, 5n) 580 200 min-1

103 256Lr 27 s 249Cf(11B, 4n) 122 40 min-1

104 261Rf 68 s 248Cm(18O, 5n) 13 4 min-1

105 262Db 35 s 249Bk(18O, 5n) 6 2 min-1

106 265Sg 14 s/9 s 248Cm(22Ne, 5n) 0.38 6 h-1

107 267Bh 17 s 249Bk(22Ne, 4n) 0.07 2 h-1

108 269Hs 10 s 248Cm(26Mg, 5n) 0.007 3 d-1

112 283Cn 4 s 242Pu(48Ca, 3n)287Fl

→283Cn

0.004 2 d-1

* Assuming typical values of 0.8 mg/cm2 for the target thickness and beam intensities

of 3 x 1012 particles per second.

12

Atom-at-a-time chemistry

Because of the short half-lives and the low production rates of

the heaviest nuclides, each atom produced decays before a

new atom is synthesized.

Any chemistry to be performed must be done on an "atom-at-

a-time" basis.

This imposes stringent limits on experimental procedures.

Rapid and very efficient radiochemical procedures must be

devised.

13

Atom-at-a-time experiments

1. Gas-phase chemistry:

▶ Thermochromatography

▶ Isothermal chromatography

Talk by A. Türler (IA-518)

2. Liquid-phase chemistry:

▶ Liquid-liquid extraction

▶ Ion-exchange chromatography

▶ Reversed-phase extraction chromatography

▶ Redox chromatography

14

▶ Chemical properties of element 106 (seaborgium)

M. Schädel et al, Nature 388, 55 (1997).

▶ Chemical characterization of bohrium (element 107)

R. Eichler et al., Nature 407, 63 (2000).

▶ Chemical investigation of hassium (element 108)

Ch. E. Düllmann et al., Nature 418, 859 (2002).

▶ Chemical characterization of element 112

R. Eichler et al., Nature 447, 72 (2007).

▶ Synthesis and detection of a seaborgium

carbonyl complex

J. Even et al., Science 345, 1492 (2014).

▶ Measurement of the first ionization

potential of lawrencium, element 103

T. K. Sato et al., Nature 520, 209 (2015).

▶ Atom-at-a-time laser resonance ionization

spectroscopy of nobelium

M. Laatiaoui et al., Nature 538, 495 (2016).

Highlighted chemical studies

15

Nucl. Phys. A

944, 1-690 (2015)

Special Issue on

Superheavy Elements

Edited by

Christoph E. Düllmann,

Rolf-Dietmar Herzberg,

Witold Nazarewicz and

Yuri Oganessian

Recent review articles

Chem. Rev. 113, 1237-1312 (2013)

(2014)

M. Schädel and D. Shaughnessy. Eds

16

Presentation in APSORC2017

Overview

A. Türler (IA-518): A postcard from the island of stability: what’s new in superheavy

element chemistry

Production & Nuclear reaction mechanism

J. V. Kratz (A-036): Radiochemical investigation of the kinematics of multi-nucleon

transfer reactions in 48Ca + 248Cm collisions 10% above the

Coulomb barrier

H. Haba (A-079): Production and decay studies of 261Rf, 262Db, 265Sg, and 266Bh for

superheavy element chemistry at RIKEN GARIS

17

Presentation in APSORC2017

Liquid-phase chemistry

Y. Komori (A-078): Development of a rapid solvent extraction apparatus coupled to

the GARIS gas-jet transport system to aqueous chemistry of the

heaviest elements

Gas-phase chemistry & atomic properties

T. Tomitsuka (A-209): Adsorption of lawrencium (Z = 103) on a Ta surface

N. M. Chiera (A-160): Unexpected transport to the cryo-on-line-detector COLD)

setup of a volatile At species

K. Shirai (A-035): Influence of surface condition of quartz column for gas

chromatographic behavior of ZrCl4 and HfCl4

Y. Nagame (A-259): First ionization energies of heavy actinides

Development of new innovative apparatuses !

18

2. Recent liquid-phase chemistry

Atom-at-a-time chemistry:

To get statistically significant results with single atoms, it is indispensable to repeat the

same experimental procedure several hundred or even several thousand times with

cycle times of about the lifetime of the nuclide under investigation.

The behavior of the heaviest elements is compared with that of its lighter homologs

under identical conditions.

Extensive series of detailed investigations have been made possible by the

development of computer-controlled automated systems that have greatly

improved the ability

▶ to perform rapidly and reproducibly large numbers of chemical (chromatographic)

separations on miniaturized columns and

▶ to systematically vary ligand concentrations, thus allowing determining the

stoichiometry of the eluted species: Kd vs. [ligand].

The experiments with automated devices have produced detailed and

sometimes surprising results that called for a detailed theoretical modeling of

the chemical properties with improved quantum-chemical calculations.

19

Recent highlighted liquid-phase chemistry

2-1. Complex formation of 104Rf

- Fluoride complex formation of Rf

complex formation abilities

2-2. Electrochemistry of 101Md & 102No

- Redox reactions of Md & No

oxidation states & redox potentials

20

Experiments with Rf in the liquid-phase

1. Production of a specific heaviest nuclide

2. Rapid transport of this nuclide to chemical separation devices

3. Fast chemical characterization that includes dissolution in an aqueous solution

containing inorganic/organic ligands for complex formation

4. Preparation of a sample

suitable for α-spectroscopy

5. Detection of nuclides

through their characteristic

nuclear decay properties

for unambiguous

identification

Automated rapid chemistry apparatuses

ARCA II and AIDA

The automated rapid

chemistry apparatuses

ARCA II and AIDA enable

cyclic column

chromatographic separation.

21 21

Eluent bottles

Ta disk reservoir

Micro-columns

He gas heater Halogen lamp

Sampling table

Air cylinder

Pulse motors Signal out

8 vacuum chambers

600 mm2 PIPS detectors

Preamp.

He/KCl gas-jet

Cyclic discontinuous column chromatographic separation of short-lived nuclides &

automated detection of α-particles within a typical cycle time of 60 s

ARCA II

AIDA: Automated Ion-exchange separation apparatus coupled

with the Detection system for Alpha-spectroscopy

22

Photo of AIDA

23

2-1. Fluoride complex formation of Rf

248Cm(18O, 5n)261Rf (T1/2 = 68 s) : σ = 13 nb

Experimental approach should involve detailed comparison of the chemical

properties of the heaviest elements with those of their lighter homologues

under identical conditions.

1 18

1 2

2 13 14 15 16 17

3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18

3 4 5 6 7 8 9 10 11 12

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118

57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

89 90 91 92 93 94 95 96 97 98 99 100 101 102 103

Es FmPa U Np MdPu

Sm GdCe Tm

No LrAm BkCm CfAc ThActinides

YbLa Pr Nd PmLanthanides

DsHsDb Sg BhFr Ra Ac Rf

PdRh

Lu

Mt

Tb Dy Ho ErEu

Rg Lv

Os Ir Pt Au

Nh McCn Fl

Re RnHg Tl Pb Bi AtPoCs Ba La

MoNbZrY

Ta WHf

As

Sr

Br Kr

Rb XeITeSbSn

V

Cd

Mn Fe Co Ge

InRuTc Ag

He

Be B NeF

Se

NC

Cl ArP

Cr

H

Li

Na Mg

K Ca Sc Ti

S

O

Ts Og

Al

Ni Cu Zn Ga

Si

24

Fluoride complex formation of Rf

John Emsley,

in NATURE’S BUILDING

BLOCKS, Oxford 2011

Rutherfordium: Element of surprise

▶ Rutherfordium is not like the higher member of group 4 in

its behavior with fluoride ions.

▶ Like hafnium and zirconium, it forms a complex ion with six

fluorides: RfF62- but it does not form RfF7

3- whereas the

other two metals do.

▶ The reason appears to be that relativistic effects are

coming into play and these affect the behavior of its

bonding electrons.

H. Haba et al., J. Am. Chem. Soc.

126, 5219 (2004).

25

2-2. Electrochemistry of Md & No

Redox studies of the heaviest elements are expected to give valuable

information on valence electronic states influenced by strong relativistic

effects, such as oxidation states & redox potentials.

Reduction of 101Md : Md3+ Md2+

Oxidation of 102No : No2+ No3+

248Cm(11B, 4n)255Md (T1/2 = 27 min)

248Cm(12C, 5n)255No (T1/2 = 3.1 min)

• Development of a rapid electrochemical

apparatus

• Redox reactions with an atom-at-a-time

technique

Solution

26

Flow electrolytic column chromatography

26

Working electrode

(Glassy carbon fibers) Reference

electrode

(Ag/AgCl)

Carbon rod

Inlet

Md3+

Md3+

Carbon fiber

Md2+

e－ e－

Flow

Counter

electrode

(Pt)

Outlet

Md2+

Rapid & effective redox reactions

Electrolyte solution: 0.1 M HCl

A. Toyoshima et al.,

Radiochim. Acta 96, 323-326 (2008).

▶ Both electrochemical and cation-exchange reactions in the column

▶ Different cation-exchange behavior between the different oxidation

states

Cation-exchanger (Nafion)

27

Redox reactions of Md & No

0

20

40

60

80

100

120

-1.5 -1 -0.5 0 0.5

Reduction p

robabili

ty / %

Applied potential / V

0

20

40

60

80

100

120

-0.5 0 0.5 1 1.5

Oxid

atio

n p

rob

abili

ty /

%

Applied potential / V

▶ Redox reactions based on an atom-at-a-time scale were successfully

conducted with the newly developed flow electrochemical apparatus.

▶ This new technical approach will open up new frontiers of the

chemistry of the transactinide elements.

A. Toyoshima et al.,

Inorg. Chem. 52, 12311-12313 (2013).

A. Toyoshima et al.,

J. Am. Chem. Soc. 131, 9180-9181 (2009).

No2+ ⇄ No3+ + e- Md3+ + e- ⇄ Md2+

Eu3+ +e- ⇄ Eu2+

28

3. Atomic properties of the heaviest actinides

Study of atomic properties of the heaviest elements is indispensable to

understand electronic ground state configurations.

The first ionization potential/energy (IP1) is an atomic property which most

sensitively reflects the outermost electronic configuration.

Precise and accurate determination of IP1 provides significant information on

the binding energy of the valence electrons and, thus, on increasingly strong

relativistic effects.

Inner electron orbital

Expansion

Nucleus

Outer electron orbital

Electron

Contraction

29

3-1. First ionization energy (IP1) of Lr

Cover of Nature：

9 April 2015

EXTREME

CHEMISTRY

Experiments on rare lawrencium

atoms illuminate a relativistic

region of the periodic table

30

Valence electronic structure of Lr

The ground-state electronic configuration of Lr is predicted to be [Rn]5f147s27p1/2, in

contrast to that of its lanthanide homolog Lu, [Xe]4f146s25d, as the7p1/2 orbital is

expected to be stabilized below the 6d orbital in Lr by strong relativistic effects.

The determination of IP1 sheds light on the important role of relativistic effects on the

electronic structure of heavy elements.

Lr: [Rn]5f147s27p1/2

Lu: [Xe]4f146s25d

No IP1 data beyond Es

(Z = 99)

⇒ New “atom-at-a-time”

technique

1 18

1 2

2 13 14 15 16 17

3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18

3 4 5 6 7 8 9 10 11 12

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118

57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

89 90 91 92 93 94 95 96 97 98 99 100 101 102 103

S

O

Ts Og

Al

Ni Cu Zn Ga

Si P

Cr

H

Li

Na Mg

K Ca Sc Ti

He

Be B NeF

Se

NC

Cl Ar

V

Cd

Mn Fe Co Ge

InRuTc Ag

As

Sr

Br Kr

Rb XeITeSbSn

Cs Ba La

MoNbZrY

Ta WHf Re RnHg Tl Pb Bi AtPo

Lv

Os Ir Pt Au

Nh McCn Fl

PdRh

Lu

Mt

Tb Dy Ho ErEu

Rg

Lanthanides

DsHsDb Sg BhFr Ra Ac Rf

Ac ThActinides

YbLa Pr Nd Pm Sm GdCe Tm

No LrAm BkCm Cf Es FmPa U Np MdPu

⇒ the heaviest

element ion beams

31

Valence electronic structure of Lr

The ground-state electronic configuration of Lr is predicted to be [Rn]5f147s27p1/2, in

contrast to that of its lanthanide homolog Lu, [Xe]4f146s25d, as the7p1/2 orbital is

expected to be stabilized below the 6d orbital in Lr by strong relativistic effects.

The determination of IP1 sheds light on the important role of relativistic effects on the

electronic structure of heavy elements.

Lr: [Rn]5f147s27p1/2

Lu: [Xe]4f146s25d

No IP1 data beyond Es

(Z = 99)

⇒ New “atom-at-a-time”

technique

1 18

1 2

2 13 14 15 16 17

3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18

3 4 5 6 7 8 9 10 11 12

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118

57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

89 90 91 92 93 94 95 96 97 98 99 100 101 102 103

S

O

Ts Og

Al

Ni Cu Zn Ga

Si P

Cr

H

Li

Na Mg

K Ca Sc Ti

He

Be B NeF

Se

NC

Cl Ar

V

Cd

Mn Fe Co Ge

InRuTc Ag

As

Sr

Br Kr

Rb XeITeSbSn

Cs Ba La

MoNbZrY

Ta WHf Re RnHg Tl Pb Bi AtPo

Lv

Os Ir Pt Au

Nh McCn Fl

PdRh

Lu

Mt

Tb Dy Ho ErEu

Rg

Lanthanides

DsHsDb Sg BhFr Ra Ac Rf

Ac ThActinides

YbLa Pr Nd Pm Sm GdCe Tm

No LrAm BkCm Cf Es FmPa U Np MdPu

⇒ the heaviest

element beams

Y. Nagame,

Nature Chem. 8, 282 (2016)

32

Experimental set-up

Complex system: surface ionization, mass separation and detection of Lr ions

249Cf target

11B beam

Gas-jet transport

Skimmer

Ionization

cavity Extraction

electrode

Ion source

α-particle

detector

T. K. Sato et al.

Nature 520, 209 (2015)

Mass separation

Lr atoms are ionized to the +1 charge state via the

interaction with a solid metal surface at high temperature

and is selectively mass-separated from nuclear reaction

by-products.

249Cf(11B, 4n)256Lr

33

First ionization energy (IP1) of Lr

IP / eV

Exp. 4.96 ± 0.08

Cal. 4.963*

The good agreement with theoretical prediction

obtained using relativistic calculations, which

favor a 7s27p1/2 configuration in the Lr atom,

supports this ground state configuration.

This quantitatively reflects and confirms the theoretically predicted situation of

closed 5f14 and 7s2 shells with an additional weakly-bound electron in the

valence orbital. ⇒ Lr: last actinide ⇒ actinide series in the Periodic Table

Lanthanides

Actinides

34

5. Summary & Perspectives

Liquid-phase chemistry

▶ Surprising chemical properties of Rf (and 105Db)

▶ Heavier elements:

New technical development: Continuously working system consisting

of a rapid chemical separation device and a flow-through α-particle

detection apparatus, coupled to a recoil pre-separator

Talk by Y. Komori (A-078)

New approach with the heaviest element (ion) beams

▶ IP1 Talk by Y. Nagame (A-259)

▶ Adsorption behavior of Lr Talk by T. Tomitsuka (A-209)

▶ Ion beams, Atomic & Molecular beams New frontier chemistry

35

ChemHaiku

Oganesson (Og)

The end of the line,

your millisecond half-life

brings down the curtain

P. Pyykkö, PCCP 13, 161 (2011)

33

Suggested Periodic Table up to Z ≤ 172

37

Thank you for your attention

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