Topical Science: The International Year of the Periodic Table

Topical Science

Topical

January 2019

The International Year of the Periodic Table of the Chemical Elements

The Periodic Table This year, 2019, is the 150 anniversary of the Periodic Table of the chemical elements, which was developed by the Russian scientist Mendeleev in 1869. To mark this, UNESCO has designated 2019 as The International year of the Periodic Table. th

There are thousands of chemical compounds, but they are all composed of various combinations of chemical elements, of which only about 90 occur naturally. In 1869, Mendeleev arranged all of the then known elements in increasing order of their atomic masses. He found that similar properties occurred periodically as he went through the sequence, so he drew up a table, placing elements with similar properties in the same vertical group.

Not all of the chemical elements had been discovered by the 1860s. Mendeleev left gaps in the periodic Table where he predicted that elements, yet to be discovered, would fit in.

Dmitri Mendeleev Mendeleev was born in Siberia in 1834, the youngest of a large family. In 1849, following his father’s death, his mother brought him to St. Petersburg, where he attended University.

After graduating, he moved to the Crimea, to begin a teaching career as a science master. He later moved back to St. Petersburgh, where he eventually secured a university post and established an important centre there for chemical research.

He was awarded the Nobel Prize for Chemistry in 1906 for his work in developing the Periodic Table.

He died the following year, at the age of 72.

The Modern Periodic Table The layout of the modern Periodic Table of the chemical elements is shown above. The numbers 1 to 18 at the top give the group number. Elements in the same group have similar chemical properties.

In Mendeleev’s time, nothing was known about atomic structure. According to Dalton’s Atomic Theory, each element was made up of one type of atom only and elements were characterized by their atomic masses. But later discoveries showed that atoms have an internal structure, with a nucleus consisting of particles called protons, which have a positive charge and neutrons, which are electrically neutral. The space outside the nucleus is occupied by tiny negatively charged particles called electrons, which are in constant motion. Atoms as a whole are neutral, so that the number of electrons in an atom is equal to the number of protons in its nucleus.

What makes each element unique is not its atomic mass, but the number of positively charged protons in the nucleus of its atoms. This is called the Atomic Number. Atoms of a given element all have the same atomic number, but the number of neutrons may vary, so that atoms of the same element do not all have the same atomic mass. The mass number is obtained by adding together the number of protons and neutrons in the nucleus, Atoms with the same atomic number but different mass number are known as isotopes. Usually one isotope is much more abundant that the others. For example, most carbon atoms have a mass no. 12, but there is a heavier isotope with mass of 13 and an unstable, radioactive isotope with mass no. 14. These are given symbols C12, C13 and C14 respectively.

In the table above, elements are arranged according to their atomic numbers, starting with hydrogen, no. 1, which has only one proton in the nucleus of its atoms. Each element has a symbol, consisting of one or two letters. The atomic numbers are shown above the symbol and the masses (calculated as the weighted average of the masses of the isotopes) are shown underneath. The table is divided into blocks, shown in different colours, according to the electronic structure of its atoms. The electrons are arranged in layers or ‘shells’ around the nucleus and it is the number of outer electrons, which determine the properties of an element. Groups 1 & 2 (n blue) are all highly reactive metals, with only 1 or 2 electrons in the outer shell of their atoms. The non-metals, metalloids and less reactive metals are on the right, shown in orange, while transition metals are in the middle.

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Events to mark the international Year of the Periodic Table.

The Opening Ceremony will take place at UNESCO in Paris on the 29th January 2019 The programme will include welcome addresses, an exhibition, the showing of a video celebrating IYPT2019, round table discussions, musical interludes, an address by Nobel Laureate Ben Feringa (who discovered graphene) and presentations by Martyn Poliakoff, who has made videos of every element in the Periodic Table and Yuri Oganessian, who has the heaviest element, No. 118, named Oganesson after him.

Chemical societies all over the world will hold events to mark the year.

The Interna tional Year of the Periodi c Table of the Elemen ts 2019

The International Union for Pure & Applied Chemistry (IUPAC) has designed an on-line quiz, where you can test your knowledge of the Periodic Table. It is called the ‘Get in your Element’ challenge. If you score sufficient points, you become eligible to enter the more creative Nobelium Contest.

If you want to have a go, here’s the link: https://iupac.org/100/pt-challenge/ To find out more about the International year of the Periodic Table and the events taking place to mark it, visit the official website here: https://www.iypt2019.org/

FOCUS on the element COBALT Cobalt (symbol Co) is element number 27 in the periodic Table. It is in the central block in the Periodic Table, in the first row of the transition elements. Many of its compounds are blue in colour and in fact ‘cobalt blue’ is a well-known artist’s pigment. Cobalt may be added to glass to give a beautiful blue colour, seen in glass bottles and stained glass windows. The metal is rarely encountered in the pure state, but is used in certain alloys. It is an essential element for life, as it occurs in vitamin B12. The most abundant isotope of cobalt has an atomic mass number of 59. Cobalt also has a heavier isotope Co60, which is unstable and therefore is radioactive. It is used commercially as a radioactive tracer.

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Completion of the Periodic Table.

Since the time of Mendeleev, the remaining naturally occurring chemical elements, unknown in his day, have been discovered. All the gaps that Mendeleev had to leave blank, in his Periodic Table, have now been filled. These elements all exhibit the properties that Mendeleev predicted. This validates his classification of the elements.

In addition, a number of elements with atomic numbers greater than uranium (atomic number 92) have now been synthesized in large atomsmashing machines. These elements are highly unstable and because of this, they decay very rapidly by radioactivity. This is the reason why they are not found in rocks and minerals in the earth’s crust. Uranium itself is also radioactive, but it has a very long half-life and because of this, it still is found in significant quantities in ores such as pitchblende and it occurs in trace amounts in a variety of rocks, such as granite.

The Periodic Table is now complete, up to element number 118. This element was first synthesised in the year 2002 in Dubna, near Moscow and has been named Oganesson, after the Russian scientist Yuri Oganessian, who was one of the principal nuclear physicists involved in the discovery of these new elements. So the wheel has come full circle, as the Periodic Table started in Russia and has now been completed in Russia.

About the Author called ‘Topical Science’ in a local weekly newspaper, ‘The Westmeath Independent’.

The aim of ‘Topical Science’ is to explain in plain language the science behind topical news items.

Margaret was also a regular contributor to ‘Science Spin’ magazine, which unfortunately is now out of print.

During this International Year of the Periodic Table, a different element will be featured each month in this newsletter.

Cobalt has been featured in this issue, as the element for January.

Oganessian, now in his 80s, will be one of the speakers at the opening ceremony in Paris later this month, where he will talk about the ‘newcomers’ to the Periodic Table.

Margaret Franklin, the author of this newsletter, is a retired chemistry lecturer, who lives in the Republic of Ireland.

For several years she published a column

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