Periodic Table > Americium
 

Terminology


Allotropes
Some elements exist in several different structural forms, these are called allotropes.


For more information on Murray Robertson’s image see Uses/Interesting Facts below.

 

Fact Box Terminology


Group
Elements appear in columns or ‘groups’ in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.


Period
Elements are laid out into rows or ‘periods’ so that similar chemical behaviour is observed in columns.


Block
Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp, principal, diffuse, and fundamental.


Atomic Number
The number of protons in the nucleus.


Atomic Radius/non -bonded (Å)
based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties, for more details please refer to the CRC Handbook of Chemistry and Physics.


Electron Configuration
The arrangements of electrons above the last (closed shell) noble gas.


Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.


Melting Point (oC)
The temperature at which the solid-liquid phase change occurs.


Melting Point (K)
The temperature at which the solid-liquid phase change occurs.


Melting Point (oF)
The temperature at which the solid-liquid phase change occurs.


Boiling Point (oC)
The temperature at which the liquid-gas phase change occurs.


Boiling Point (K)
The temperature at which the liquid-gas phase change occurs.


Boiling Point (oF)
The temperature at which the liquid-gas phase change occurs.


Sublimation
Elements that do not possess a liquid phase at atmospheric pressure (1 atm) are described as going through a sublimation process.


Density (kgm-3)
Density is the weight of a substance that would fill 1 m3 (at 298 K unless otherwise stated).


Relative Atomic Mass
The mass of an atom relative to that of Carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists the value given is the abundance weighted average.


Key Isotopes (% abundance)
An element must by definition have a fixed number of protons in its nucleus, and as such has a fixed atomic number, however variants of an element can exist with differing numbers of neutrons, and hence a different atomic masses (e.g. 12C has 6 protons and 6 neutrons and 13C has 6 protons and 7 neutrons).


CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems (where several isotopes exist, a value is presented for the most prevalent isotope).

Fact Box

 
Group Actinides  Melting point 1176 oC, 2148.8 oF, 1449.15 K 
Period Boiling point 2011 oC, 3651.8 oF, 2284.15 K 
Block Density (kg m-3) 13670 
Atomic number 95  Relative atomic mass 243.061  
State at room temperature Solid  Key isotopes 241Am, 243Am 
Electron configuration [Rn] 5f77s2  CAS number 7440-35-9 
ChemSpider ID 22405 ChemSpider is a free chemical structure database
 

Interesting Facts terminology


Image Explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.


Natural Abundance

Where this element is most commonly found in nature.


Biological Roles

The elements role within the body of humans, animals and plants. Also functionality in medical advancements both today and years ago.


Appearance

The description of the element in its natural form.

Uses / Interesting Facts

 
Image explanation
A combination of imagery reflecting the origin of the element’s name and the presence of the element in domestic smoke alarms.
Appearance
A man-made radioactive metal, a few grammes of which are produced from plutonium in nuclear reactors each year.
Uses
Americium has few uses other than in smoke alarms. It is of interest as it is part of the decay sequence that occurs in nuclear power production.
Biological role
Americium has no known biological role. It is toxic due to its radioactivity.
Natural abundance
Americium can be prepared chemically by the reduction of americium(Ill) fluoride with barium, or americium(IV) oxide with lanthanum. However, it is produced in nuclear reactors by the neutron bombardment of plutonium, and this is the greatest source of the element.
 
Atomic Data Terminology

Atomic radius/non -bonded (Å)
Based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties,for more details please refer to the CRC Handbook of Chemistry and Physics.


Electron affinity (kJ mol-1)
The energy released when an additional electron is attached to the neutral atom and a negative ion is formed (where several isotopes exist, a value is presented for the most prevalent isotope). *


Electronegativity (Pauling scale)
The degree to which an atom attracts electrons towards itself, expressed on a relative scale as a function bond dissociation energies, Ed in eV. χA - χB =(eV)-1/2sqrt(Ed(AB)-[Ed(AA)+Ed(BB)]/2), with χH set as 2.2 (where several isotopes exist, a value is presented for the most prevalent isotope).


1st Ionisation energy (kJ mol-1)
The minimum energy required to remove an electron from a neutral atom in its ground state (where several isotopes exist, a value is presented for the most prevalent isotope).


Covalent radius (Å)
The size of the atom within a covalent bond, given for typical oxidation number and coordination (where several isotopes exist, a value is presented for the most prevalent isotope). ***

Atomic Data

 
Atomic radius, non-bonded (Å) 2.440 Covalent radius (Å) 1.73
Electron affinity (kJ mol-1) Unknown Electronegativity
(Pauling scale)
Unknown
Ionisation energies
(kJ mol-1)
 
1st
576.384
2nd
-
3rd
-
4th
-
5th
-
6th
-
7th
-
8th
-
 

Mining/Sourcing Information

Data for this section of the data page has been provided by the British Geological Survey. To review the full report please click here or please look at their website here.


Key for numbers generated


Governance indicators

1 (low) = 0 to 2

2 (medium-low) = 3 to 4

3 (medium) = 5 to 6

4 (medium-high) = 7 to 8

5 (high) = 9


Reserve base distribution

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %

(Where data are unavailable an arbitrary score of 2 was allocated. For example, Be, As, Na, S, In, Cl, Ca and Ge are allocated a score of 2 since reserve base information is unavailable. Reserve base data are also unavailable for coal; however, reserve data for 2008 are available from the Energy Information Administration (EIA).)


Production Concentration

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %


Crustal Abundance

1 (low) = 100 to 1000 ppm

2 (medium-low) =10 to 100 ppm

3 (medium) = 1 to 10 ppm

4 (medium-high) = 0.1 to 1 ppm

5 (high) = 0.1 ppm

(Where data are unavailable an arbitrary score of 2 was allocated. For example, He is allocated a score of 2 since crustal abundance data is unavailable.)


Explanations for terminology


Crustal Abundance (ppm)

The abundance of an element in the Earth's crust in parts-per-million (ppm) i.e. The number of atoms of this element per 1 million atoms of crust.


Sourced

The country with the largest reserve base.


Reserve Base Distribution

This is a measure of the spread of future supplies, recording the percentage of a known resource likely to be available in the intermediate future (reserve base) located in the top three countries.


Production Concentrations

This reports the percentage of an element produced in the top three countries. The higher the value, the larger risk there is to supply.


Total Governance Factor

The World Bank produces a global percentile rank of political stability. The scoring system is given below, and the values for all three production countries were summed.


Relative Supply Risk Index

The Crustal Abundance, Reserve Base Distribution, Production Concentration and Governance Factor scores are summed and then divided by 2, to provide an overall Relative Supply Risk Index.

Supply Risk

 
Scarcity factor Unknown
Country with largest reserve base Unknown
Crustal abundance (ppm) Unknown
Leading producer Unknown
Reserve base distribution (%) Unknown
Production concentration (%) Unknown
Total governance factor(production) Unknown
Top 3 countries (mined)
  • Unknown
Top 3 countries (production)
  • Unknown
 

Oxidation states/ Isotopes


Key for Isotopes


Half Life
  y years
  d days
  h hours
  m minutes
  s seconds
Mode of decay
  α alpha particle emission
  β negative beta (electron) emission
  β+ positron emission
  EC orbital electron capture
  sf spontaneous fission
  ββ double beta emission
  ECEC double orbital electron capture

Terminology


Common Oxidation states
The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Free atoms have an oxidation state of 0, and the sum of oxidation numbers within a substance must equal the overall charge.


Important Oxidation states
The most common oxidation states of an element in its compounds.


Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.

Oxidation States / Isotopes

 
Common oxidation states 6, 5, 4, 3
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  241Am 241.057 - 432.7 y  α 
        1.2 x 1014 sf 
  243Am 243.061 - 7.37 x 103 α 
        2 x 1014 sf 
 

Pressure and Temperature - Advanced Terminology


Molar Heat Capacity (J mol-1 K-1)

Molar heat capacity is the energy required to heat a mole of a substance by 1 K.


Young's modulus (GPa)

Young's modulus is a measure of the stiffness of a substance, that is, it provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.


Shear modulus (GPa)

The shear modulus of a material is a measure of how difficult it is to deform a material, and is given by the ratio of the shear stress to the shear strain.


Bulk modulus (GPa)

The bulk modulus is a measure of how difficult to compress a substance. Given by the ratio of the pressure on a body to the fractional decrease in volume.


Vapour Pressure (Pa)

Vapour pressure is the measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure / Temperature - Advanced

 
Molar heat capacity
(J mol-1 K-1)
Unknown Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) Unknown
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - 3.88
x 10-7
1.67
x 10-3
0.423 21.35 - - - - -
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History

This element was in fact discovered after curium, the element which follows it in the periodic table. However, it did once exist on Earth having been produced for millions of years in natural nuclear reactors in Oklo, Gabon. These ceased to function a billion years ago, and as the longest lived isotope is americium-247, with a half-life of 7370 years, none has survived to the present day. Americium was first made late in 1944 at the University of Chicago by a team which included Glenn Seaborg, Ralph James, Leon Morgan, and Albert Ghiorso. The americium was produced by bombarding plutonium with neutrons in a nuclear reactor. This produced isotope americium-241, which has a half-life of this is 432 years.

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Podcasts

Listen to Americium Podcast
Transcript :

Chemistry in Its Element - Americium


  (Promo)

You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry

(End promo)

Chris Smith 

Elementary envy tops the bill this week with a substance that was christened to compete with Europium.   It was announced to the world via the slightly unorthodox route of a kids' radio show, but this stuff is none the less worth its weight in gold, in fact its worth more than that, 60 times as much in fact, because its gone on to save thousands of lives and homes around the world since.   And to tell us how here's Brian Clegg

Brian Clegg

Keeping up with the neighbours is rarely a concern in the periodic table. Nitrogen doesn't care much what carbon and oxygen are up to, and rarely casts covetous glances at phosphorous. But there's at least one substance in the periodic table that was named in response to a nearby element, and that's americium, the element that looks as if it should be pronounced [AMER-ICK-IUM].

It sits in the seventh position in the actinides, those mostly artificial substances that inhabit the second of the periodic table's floating bars of elements, and directly above it, in the parallel list of lanthanides, you will find europium. Americium's name, according to its discoverers, is 'suggested on the basis of its position. analogous to europium' - but let's face it, you could equally blame its name on continent envy. However it was dreamed up, it's an improvement on the provisional names given to americium and curium (discovered at the same time) - originally they were pandemonium and delirium.

Americium didn't exist until Glen T. Seaborg and his colleagues, working on the Manhattan Project in the Metallurgical Laboratory at the University of Chicago, produced it in 1944. It feels strange to say that Seaborg took out a patent on this 'element 95'. Seaborg's team would isolate a total of 10 new elements, re-arranging the structure of the periodic table.

The first hint the world had of the existence of americium came not in a paper for a distinguished journal, but on a children's radio quiz in 1945. Seaborg appeared as a guest on NBC's Quiz Kids show, where one of the participants asked him if they had produced any other new elements as well as plutonium and neptunium. As Seaborg was due to formally announce the discovery of americium five days later, he let slip its existence, along with element 96, later called curium.

The first isotope of americium produced was americium 241, still the most commonly used form. The Manhattan Project was busy creating plutonium to be used in nuclear weapons, and some plutonium 239 went through a process of capturing extra neutrons to become 240 and then 241, which gave off an electron from the nucleus to turn into americium.

None of americium's isotopes are truly stable - the longest lasting, americium-243, has a half-life of 7370 years, while many of the 18 isotopes produced only hang around for minutes. Like many of the actinides, Americium is silver-white in appearance, and reasonably heavy with a density similar to that of lead. It's a solid at room temperature - you'd need to heat it to over 1,000 degrees Celsius to melt it.

But americium has one unique quality. It's the only artificial element - and the only radioisotope - that is routinely found in the home.

Actually, I ought to qualify that. We all have traces of natural radioactive elements in our houses. If you live somewhere like Cornwall with a high preponderance of granite, you will have more than your fair share, for instance, of radon about the place, giving a background radiation level of three times that experienced in London. But americium is the only radioisotope you are likely to go down to the supermarket and buy - what's more, you will have been encouraged to do so by the government.

That's because americium is used in many smoke detectors. A tiny quantity - less than a millionth of a gram - of americium 241 oxide will be sitting in there, beaming out radiation as it slowly transforms to neptunium with a half life of 432 years. The alpha particles flowing from the americium (it's a better alpha source than radium) pass through a small compartment where they ionize the air, allowing a tiny electrical current to cross the chamber. If smoke particles get in there, they absorb the alpha particles before they can create ions, stopping the current flowing and setting off the alarm.

Every now and then someone will panic when they discover that not only is there a radioactive material in household smoke detectors, but it could, in principle, be used to produce a nuclear weapon. Assemble enough of that americium-241 and it would go critical. But before any terrorist groups try to corner the market in smoke detectors it's worth pointing out that it would take around 180 billion of them to have sufficient americium-241 assembled to go critical - and even then it wouldn't be enough to put the detectors together in the same place, you would have to painstakingly extract each of those 180 billion specks of the element and mould them together, an effort that would take thousands of years.

Americium has also found other uses for its radioactive emissions, as a source of both alpha particles and gamma rays for medical applications and in industry - but its use is limited to jobs where only a small quantity is required, as it is expensive to produce. The americium oxide used in smoke detectors costs around $1500 per gram - compare this with the current gold price of around $30 per gram. There's a nice irony that the element named after the world's richest, most consumption-oriented nation is only typically used in very small quantities. 

One of my favourite books in my youth was Isaac Asimov's Foundation. In this book, tiny, walnut sized atomic generators are commonplace. This was one of science fiction's dreams that never came true - and many people would now be horrified at the thought of personal use of nuclear power. Yet this one element, americium, is the radioactive heart that helps keep our homes safe.

Chris Smith

Brian Clegg with the element that was born out of envy, but I'm not sure if its compounds are green though.   But next week's element certainly is, the discoverer named Thallium after the Greek word thallos, meaning "green shoot".   But don't get distracted by its colour, because this stuff is deadly, sufficiently nasty in fact for Agatha Christie to have written a murder mystery about it.   

Henry Nicholls

I slammed back the receiver, then took it off again.   I dialled the number and was lucky enough this time to get Lejeune straight away.   "Listen" I said, "is Ginger's hair coming out by the roots in handfuls?" "Well as a matter of fact I believe it is.   High fever I suppose."   "Fever my foot" I said "what Ginger's suffering from, what they've all suffered from is Thallium poisoning, please God may we be in time."

Chris Smith

And you can hear how Ginger gets on from Henry Nicholls on next week's Chemistry in its Element, do try and join us.   I'm Chris Smith, thank you for listening and goodbye.   

(Promo)

Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists dot com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld dot org forward slash elements. 

(End promo)

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References

 
Images:  Visual Elements © Murray Robertson 2011
Mining and Sourcing data:  British Geological Survey – natural environment research council.
Text:  John Emsley Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, 2nd Edition, 2011.
Additional information for platinum, gold, neodymium and dysprosium obtained from Material Value Consultancy Ltd www.matvalue.com
Data: CRC Handbook of Chemistry and Physics, CRC Press, 92nd Edition, 2011.
G. W. C. Kaye and T. H. Laby Tables of Physical and Chemical Constants, Longman, 16th Edition, 1995.
Members of the RSC can access these books through our library.