The discovery of new elements
How are new elements discovered?
There are probably nearly as many answers to this question as there are elements. Many
elements were found more or less by accident. Others were discovered as a result of
research into a particular compound or mineral. Others were predicted to exist – on the basis
of Mendeleev’s Periodic Table, for example – so the discoverer knew what he or she was
looking for. However, from time to time a new chemical technique is developed or discovered
that leads to the discovery of several new elements in a short time. You can use the
interactive Periodic Table to investigate this idea.
Activity
The following activities are based around the interactive Periodic Table.
a) Run the Animate function and watch as the elements are displayed in the order in
which they were discovered over time. Do they seem to appear at a steady rate?
b) Use the Histogram function to plot the number of elements discovered in each
century. Does this confirm your impression?
c) Use the Between function to display histograms of the number of elements
discovered in each ten year period:
(i) between 1700 and 1800
(ii) between 1800 and 1900
(iii) between 1900 and 2000
(iv) any other time period.
You should see that there are several ten-year periods in which many elements were
discovered with periods of time in between when none were discovered. Some of the bursts
of discovery were caused by the development of new chemical techniques.
It is a great achievement to discover a single element out of the 111 or so that are now known.
So you may be surprised to find that there are several people who have discovered more than
one element, in one case as many as 11. Here are some brief descriptions of the work of
some chemists who discovered more than one element. In many cases they took advantage
of a new technique.
•
Jons Jacob Berzelius – reduction with carbon
•
Humphry Davy – electrolysis
•
Robert Bunsen – line spectra
•
William Ramsay – the distillation of liquid air
•
Marie Curie - radioactive elements
•
Glenn T Seaborg – making new elements with sub-atomic particles
Jons Jacob Berzelius – reduction with carbon
Jons Jacob Berzelius (see box) obtained four elements (thorium, cerium, selenium and
impure silicon) mainly by reduction with carbon.
Jons Jacob Berzelius
Jons Jacob Berzelius (1779 - 1848) is probably
Sweden's most famous chemist. As well as his
own discoveries, some of his colleagues also
discovered elements. Lithium was discovered by
Johann Arfvedson, whom he had trained, and
Berzelius’ former pupil in Stockholm (Carl
Mosander) discovered lanthanum, erbium and
terbium. Mosander did not use a new technique
but was fortunate to work near Ytterby - a village
near Vaxhol, Stockholm in Sweden with a quarry
where compounds containing many of the
elements of atomic numbers between 58 and 71
(called the lanthanides) were found. Berzelius was
also the first to use letter symbols for elements like
the ones we use today.
Jons Jacob Berzelius. Reproduced courtesy of the Library
and Information Centre, The Royal Society of Chemistry.
Questions
Q 1.
Berzelius used the technique of reduction with carbon to isolate elements from their
compounds. One common compound of silicon is silicon dioxide (SiO2), which is
found in sand.
(a) Give word and symbol equations for the reaction of carbon with silicon dioxide to
form silicon.
(b) Use oxidation numbers to show what is oxidised and what is reduced in the
reaction
Humphry Davy – electrolysis
Humphry Davy (see box) took advantage of new technology to discover six elements. He
used the then-newly invented voltaic pile (we would call it a battery), to electrolyse molten
salts of alkali metals so producing highly reactive metals at the negative electrode (cathode).
He obtained sodium and potassium, then magnesium, calcium, barium and strontium.
Sir Humphry Davy
Davy (1778 - 1829) was
born Cornwall but worked
in Bristol and then at the
Royal Institution in
London which is still a
prestigious centre of
scientific research. Like
many scientists at the
time Davy worked in
many fields. He
investigated the
anaesthetic properties of
dinitrogen oxide
(‘laughing gas’) on
himself, and his name will
always be associated with
the miners’ safety lamp
which he invented to
prevent explosions in
mines caused by the use
of naked flames. He was
well-known as a lecturer
and was succeeded by
his assistant, Michael
Faraday, who became
equally famous as a
scientist for developing
the electric motor and
generator.
One of Davy’s lectures at The Royal Institution. Reproduced courtesy of the Library
and Information Centre, The Royal Society of Chemistry.
Questions
Q 2.
(a) Why could Davy not isolate, say, sodium from sodium oxide by reducing the oxide
with carbon as Berzelius had done with silicon, cerium, thorium and selenium?
(b) Why did Davy electrolyse molten salts rather than solids?
(c) Why did Davy electrolyse molten salts rather than aqueous solutions?
(d) Think about the electrolysis of molten sodium chloride, which consists of Na+ ions
and Cl− ions.
(i) Write a half equation to represent the reaction that takes place at the cathode.
(ii) Is this an oxidation or a reduction?
(iii) Explain your answer to (ii).
(e) What precaution would Davy have had to take in order to obtain pure sodium at
the cathode? Explain your answer.
Robert Bunsen – line spectra
Robert Bunsen (1811 - 1899) and Gustav Kirchoff (1824 - 1887) (see box) were early users of
the technique of examining the light given out by heated compounds to recognise new
elements. Have you noticed that a wire dipped into sodium chloride solution gives an intense
yellow flame colour or that when a pan of salted water boils over it colours the gas cooker
flame yellow? This colour is characteristic of sodium and is also seen in street lamps that are
filled with sodium vapour.
The method of looking at the light given out by heated elements is still used in analysis to
measure the amounts of different elements present in a sample. It is called flame emission
spectrophotometry.
If you look at the light given out by heated elements (called an emission spectrum) through a
prism, you will see that the ‘rainbow’ of light is actually made up of groups of lines. Each
element shows a unique pattern of lines. This means that a previously-unknown group of lines
suggests a new element is present. The line spectra of some elements are shown in Figure 1.
The origin of line spectra is as follows. When atoms of an element are heated, electrons
absorb energy and jump up to higher-energy orbitals than they usually occupy. When they fall
back to lower levels, they give out ‘packets’ of electromagnetic radiation called quanta. The
more energy a quantum has, the higher frequency of radiation (shorter wavelength) it
represents. If a quantum of radiation has a wavelength of between about 400 nm and 700 nm
we can see it as visible light of a particular colour; 400 nm is purple and 700 nm red.
Robert Bunsen and
Gustav Kirchoff
In 1861 Bunsen and Kirchoff jointly discovered
caesium (which gave a blue flame) and rubidium
(which gave a red flame). Bunsen (who devised,
or at least developed, the Bunsen burner)
discovered only two elements himself, along with
Kirchoff, but his technique was used to discover
several more.
Paul Emile Lecoq de Boisbaudran (1838 - 1912)
used flame colours (called emission spectra) to
search for more elements. He discovered
gallium (1875), samarium and dysprosium.
Gallium was the first element to be found whose
properties matched elements predicted in detail
by Mendeleev in 1870, dramatic proof of his
ideas about the Periodic Table.
Kirchoff (left) and Bunsen. Reproduced courtesy of the
Library and Information Centre, The Royal Society of
Chemistry.
Figure 1 The line spectra of some elements
William Ramsay – the distillation of liquid air
William Ramsay (see box) investigated the observation that nitrogen made by removal of
other gases from air had a different density to nitrogen made by chemical decomposition.
First he discovered argon and then predicted a complete family of elements between Groups
7 and 1 of the Periodic Table. We now call these the noble gases. By fractional distillation of
liquefied air, he and Morris Travers then discovered neon, krypton and xenon. Ramsay won
the 1904 Nobel prize for chemistry.
When Ramsay discovered a gas of relative mass of approximately 40, chemists were at first
reluctant to believe that a whole new group of elements remained to be discovered. At first,
Mendeleev was a disbeliever because he felt that the discovery undermined his Periodic
Table. Later, however, he came to see that it was actually a confirmation of the basic idea
behind the Table.
Some tried to explain the new gas as an allotrope of nitrogen, N3. This seemed possible
because oxygen has an allotrope O3, usually called ozone. N3 would have a relative molecular
mass of 42, close to the measured value for argon.
Sir William Ramsay
Ramsay (1852 - 1916) was Glasgow-born but his
main research was at London University. He
discovered argon by taking a sample of air and
first removing all the oxygen. He then passed the
remaining gas (mostly nitrogen) over hot
magnesium. Magnesium is reactive enough to
combine with nitrogen to leave a solid called
magnesium nitride. After doing this repeatedly, he
was still left with some gas whose relative mass
was 40. This gas didn’t seem to fit into
Mendeleev’s Periodic Table!
Later, using newly-discovered techniques for
cooling and liquefying gases, he was able to
separate other gases from air – neon, krypton,
xenon and radon – and it was realised that he had
discovered a whole group of elements, none of
which had been known to Mendeleev. The final
member of the group, helium, had been
discovered a few years earlier – in the Sun. Pierre
Jules César Janssen had noticed some lines in the
spectrum of sunlight that didn’t belong to any
known element and suggested a new element,
which he called helium, existed in the Sun.
Ramsay was the first to recognise helium on Earth
so he discovered all of the noble gases (almost).
Sir William Ramsay. Reproduced courtesy of the
Library and information Centre, The Royal Society
of Chemistry.
Questions
Q 3.
(a) One possible way of removing oxygen from the air is to pass it over heated copper.
Write an equation for the chemical reaction that happens.
(b) Why will copper react with oxygen but will not react with nitrogen?
(c) Why will magnesium react with nitrogen?
(d) Assuming that magnesium nitride is an ionic compound, predict its formula. You
will need to use the electron arrangements of magnesium and of nitrogen to predict
what sort of ions (sign and number of charges) that each is likely to form.
(e) Using your predicted formula for magnesium nitride, write a word and a balanced
symbol equation for the reaction of magnesium and nitrogen.
Q 4.
Ramsay knew that the approximate composition of air is 20% oxygen, 80% nitrogen.
Assume 1 mole of gas has a volume of 24 dm3 at room temperature and pressure.
(a) What is the minimum mass of copper required to remove all the oxygen from 1 dm3
of air at room conditions?
(b) What is the minimum mass of magnesium required to remove all the nitrogen from
1 dm3 of air (after the removal of oxygen) at room conditions?
(c) What other gases would Ramsay have had to remove from air before he could
start his experiments? Suggest a way of removing each of these gases.
Q 5.
(a) Draw a dot and cross diagram for ozone, O3. Hint, there is one double bond and
one dative bond.
(b) You will find that it is not possible to do a similar diagram for N3 in which all three
atoms have full outer shells of electrons. Try to explain why this is not possible.
Marie Curie - radioactive elements
Marie Curie (see box), along with her husband, Pierre, investigated radioactive elements,
eventually extracting less than a gram of a new element, radium, from over eight tonnes of
the ore pitchblende.
Marie Curie
Marie Curie (1867 - 1934) discovered two elements
as she investigated what became known as
radioactivity. First she identified polonium, which
she named after her native Poland, then, with her
husband Pierre, she found the more intensely
radioactive element radium. She won the 1911
Nobel prize for chemistry for discovering the two
elements after she had shared the 1903 physics
prize with Pierre, and Henri Becquerel. She is
unique in being a double Nobel prize winner,
having a chemical element (curium) and a unit (the
curie, which measures radioactivity) named after
her.
Marie Curie and husband Pierre. Reproduced
Courtesy of the Library and Information Centre,
The Royal Society of Chemistry.
Questions
Q 6.
(a) The atomic number of radium is 88. One isotope of radium, radium-227, decays by
β-decay, that is one of the neutrons in its nucleus turns into a proton and an electrons
and the nucleus ‘spits out’ the electron. The half-life of this decay is 42 minutes.
(i) What does the term ‘isotope’ mean?
(ii) How many neutrons are there in the nucleus of an atom of radium-227?
(iii) What is the new element that is formed by β-decay of radium-227?
(iv) Starting with 1 g of radium-227, how much of it would still be radium after 126
minutes?
(b) The atomic number of polonium is 84. One isotope of polonium, polonium-209
decays by α-decay, that is the nucleus ‘spits out’ an α-particle. The half life of this
decay is 102 years.
(i) What is an α-particle? Use a web search if you are not sure.
(ii) What isotope of which element is left after this α-decay of polonium-209?
(iii) How long would it take for the radiation from a sample of polonium-209 to drop to
1/16 of its original value?
Glenn T Seaborg – making new elements with
sub-atomic particles
Glenn T Seaborg (see box), with his co-workers identified 11 elements. These all have atomic
number greater than 92 (uranium) and are man-made. The discovery that uranium atoms
could be bombarded with neutrons to create new elements led to an extension of the Periodic
Table beyond uranium.
The elements found by chemists before Seaborg were discovered – they existed on Earth
already, combined with other elements to form compounds in most cases. Chemists had to
extract them and show that they really were new elements. The elements found by Seaborg
and his colleagues were actually made – they are elements that do not exist naturally on
Earth. The heaviest element that does exist on Earth is uranium which has 92 protons.
Protons are positively charged and tend repel one another (they are held in the nucleus
against this repulsion by the strong nuclear force). Atoms whose nuclei have more than 92
protons tend to break apart because of this repulsion. This is why they are not found on Earth.
Scientists found that when they fired neutrons at uranium atoms, one would occasionally stick
to a uranium nucleus. This increased the relative atomic mass of the atom by one but kept the
atomic number the same. Sometimes this neutron then ‘spat out’ an electron and turned into a
proton. This meant that the nucleus now had 93 protons and was a new element, of atomic
number 93, which was christened neptunium, Np. This was actually done by Edwin McMillan
and Philip Abelson. Seaborg then took over, working as the leader of a group of scientists.
Bombardment with other sub-atomic particles allowed them to make elements numbers 94 103 in the same sort of way.
Glenn T Seaborg
Seaborg (1912 – 1999) won the 1951 Nobel prize for chemistry. After some argument
between the USA and the rest of the world, element 106 was named seaborgium shortly
before he died. This was a matter of some controversy because the International Union of
Pure and Applied Chemistry, IUPAC, the body that deals with naming in chemistry, had
previously ruled that elements should not be named after living people.
Glenn T Seaborg (left) with United States president John F Kennedy. Reproduced Courtesy of the Ernest Orlando
Lawrence Berkeley National Laboratory.
The elements of atomic number greater than 92 are all radioactive; their nuclei break up
changing them into different elements. In some cases, this can happen only fractions of a
second after they have been made, making it difficult to be sure that they have actually been
made. We say they have very short half lives. There are only three research centres that are
capable of making these so-called transuranic elements, one in Berkeley, California in the
USA, one in Dubna in Russia and the third in Darmstadt in the former East Germany. Often,
two centres claimed to have made a particular element first and therefore also claimed the
right to name it. A situation arose where several elements had more than one name. So, to
avoid confusion, IUPAC made a temporary ruling that the elements from atomic number 104
onwards should be named unnilquadium, unnilpentium etc from the Latin for 104, 105 and so
on. Later IUPAC examined the evidence and decided which research team had actually
discovered which element and allowed the discoverers to name them. More controversy
followed and IUPAC changed its ruling which led to further changes. So the same name was
sometimes used for two different elements at different times! The situation is summarised in
the Table below.
Atomic
number
104
105
106
107
108
109
Hassium, Hs
Meitnerium, Mt
Initially
suggested
name
Rutherfordium, Hahnium, Hn or Seaborgium, Sg
Rf or
Nielsbohrium,
Kurchatovium,
Ns
Ku
Nielsbohrium,
Ns
IUPAC
temporary
name
Unnilquadium,
Unq
Unnilpentium,
Unp
Unnilhexium,
Unh
Unnilseptium,
Uns
Agreed name
1995
Dubnium, Db
Joliotium, Jl
Rutherfordium,
Rf
Bohrium, Bh
Hahnium, Hn
Meitnerium, Mt
Agreed name
1996
Rutherfordium,
Rf
Dubnium, Db
Seaborgium, Sg
Bohrium, Bh
Hassium, Hs
Meitnerium, Mt
Unniloctium, Uno Unnilennium, Unn
Questions
Q 7.
(a) It might seem easier to make an atom of atomic number 93 by firing protons at
uranium (atomic number 92) and hoping they would ‘stick’ rather than firing neutrons,
hoping that one would ‘stick’ and then hoping that one would then turn into a proton
and an electron. Explain the problem involved with a proton sticking to a uranium
nucleus.
(b) On the relative atomic mass scale, what is the mass of
(i) a neutron,
(ii) a proton and
(iii) an electron? (Use masses to the nearest whole number.)
(c) What are the relative charges of
(i) a neutron,
(ii) a proton and
(iii) an electron?
(d) Use your answers to (b) and (c) to explain why is feasible for a neutron to turn into
a proton by ‘spitting out’ an electron.
(e) A device called a cyclotron can produce a beam of alpha particles (helium nuclei).
(i) What sub-atomic particles make up an alpha particle?
(ii) If an alpha particle is fired at an atom of uranium-238 and it ‘sticks’, what new atom
will be formed (give the name, symbol, number of neutrons and number of protons)?
Answers to questions
Q 1.
(a) silicon dioxide + carbon → silicon + carbon dioxide
Si+IVO-II2(s) + C0(s) → Si0(s) + C+IVO-II2(g)
(b) Silicon is reduced and carbon oxidised.
Q 2.
(a) Carbon is not reactive enough to remove oxygen from sodium oxide.
(b) Solid salts do not conduct electricity, while molten ones do (because the ions are
free to move in liquids but not in solids).
(c) Any sodium produced would immediately react with water / the products of the
electrolysis of water would also be formed.
(d) (i) Na+(l) + e- → Na(l)
(ii) The sodium has been reduced.
(iii) It has gained an electron.
(e) He would have had to keep it out of contact with air – hot sodium would react
rapidly with oxygen (and water vapour) in the air.
Q 3.
(a) 2Cu(s) + O2(g) → 2CuO(s)
(b) Oxygen is more reactive than nitrogen.
(c) Magnesium is a much more reactive metal than copper.
(d) Magnesium (electron arrangement 2,8,2) will form Mg2+ ions and nitrogen (electron
arrangement 2,5) will form N3- ions. So the formula will be Mg3N2.
(e) magnesium + nitrogen → magnesium nitride
Note the name of the product is magnesium nitride, not magnesium nitrate. The
ending -ide means that there are only two elements in the compound. The ending –
ate means that there are at least three elements, one of which is oxygen.
3Mg(s) + N2(g) → Mg3N2(s)
Q 4.
(a)1.07 g copper
(b) 2.4 g magnesium
(c) Carbon dioxide and water vapour. Carbon dioxide (an acidic gas) could be
removed by passing air over an alkali and water by passing it over a drying agent
such as anhydrous copper sulfate. Soda lime would remove both gases.
Q 5.
(a)
(b) There is an odd number (15) of outer electrons between the three nitrogen atoms.
Q 6.
(a) (i) Isotopes are atoms of the same element (ie they have the same numbers of
protons) but different numbers of neutrons.
(ii) 227 - 88 = 139
(iii) Actinium (atomic number 89).
(iv) This is three half lives, so 1/8 g will be left.
(b) (i) A helium nucleus, ie a group of two protons and two neutrons.
(ii) Lead-205
(iii) Four half lives, ie 408 years.
Q 7.
(a) The proton would be repelled by the positive charge of the nucleus.
(b) (i) 1,
(ii) 1,
(iii) 0
(c) (i) 0,
(ii) +1,
(iii) -1
(d) The mass and charge are conserved, ie the neutron has a mass of 1 unit and no
charge whilst a proton plus an electron also have a total mass of 1 unit and no overall
charge.
(e) (i) Two protons and two neutrons.
(ii) Plutonium-242 (Pu, 94 protons, 148 neutrons)