150 Years of Periodic Table: Test Your Knowledge


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You will find it on the wall of almost every school chemistry labs on earth.

And generations of children have sung the words "hydrogen and helium, lithium, beryllium …" in an attempt to memorize some of the 118 elements.

This year, the periodic table of chemical elements celebrates its 150th anniversary.

As the cake candles are lit, it's time to test your knowledge with our quiz.

The United Nations has designated 2019 as the International Year of the Periodic Table to celebrate "one of the most significant achievements of science".

In March, it will be 150 years since Russian scientist Dmitri Mendeleev took all known elements and arranged them at a table.

Most of his ideas stood the test of time, though it was conceived long before we knew much about the things that make up matter.

On Tuesday, the year will be officially launched in Paris. So what's so special about this iconic symbol of science?

Alien concept?

Dr. Peter Wothers of the University of Cambridge is an expert on the subject.

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Paul Wilkinson

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Chemist Peter Wothers teaches courses on the periodic table

He thinks that if aliens descend to Earth, that flag of science would not have escaped his attention.

"Would an alien have a periodic table?" he says.

"I think they probably would, because it's absolutely fundamental – it's not just a creation of humans, there's something innate and fundamental about it – there's a chemical law, a physical law behind it."

The laws of chemistry

Mendeleev (1834-1907) created his first periodic table in 1869. He took the 63 known elements and organized them on a table, mainly by their atomic mass.

Although he was not the first to do this, his interpretation involved a leap of ingenuity, in which he placed those with similar properties below each other in groups and left gaps for new elements to be embedded.

"People have been doing this for some time – but ultimately there was some natural basis – or some law – that meant they needed to be organized in some way," says Dr. Wothers.

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Wellcome Collection

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A version of the periodic table based on Mendeleev's original table

One hundred and fifty years later, there were fundamental changes in our understanding of matter.

"Obviously, Mendeleev at the time did not know anything about the atomic sub-atom structure, so he was only going for the atomic weights, which were not necessarily determined with the correct precision at the time," says Dr. Wothers.

After the discovery of the protons, scientists realized that the atomic number of an element is the same as the number of protons in its nucleus. Thus, in the modern periodic table, the elements are organized according to their atomic number – not their relative atomic mass.

"We now know the" how it works, why it works ", and this has to do with quantum mechanics and the electron arrangements in atoms and so on," he says.

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Getty Images

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The periodic table that we know today

There are now more than 100 elements, arranged in ascending order of atomic number. There are repeated patterns in the properties of the elements, which give the name to the periodic table.

Elements with similar properties are arranged to form columns (groups).

The periodic table is now a matter of beauty and practical use, says Dr. Wothers.

"You can understand certain things just by considering the place of an element in this table, or in this arrangement, that's why it's so useful to chemists."

The Joy of Symmetry

This year, which has been designated the International Year of the Periodic Table, may also represent its peak.

Currently, the seventh period of the periodic table has been completed, with the recent addition of four elements in December 2015.

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University of St Andrews

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Initial periodic table chart of about 1879 recently discovered at the University of St Andrews

That made it "pretty full and beautiful," he says.

"At the moment – in this same year – I think we are very privileged, because the periodic table is in its most perfect form," says Dr. Wothers.

"And probably the most perfect way you'll be."

People are currently working on synthesizing heavier elements, and if they manage the task, the periodic table will change again.

"As soon as one more is discovered, then we will have to start a line – the eighth period," he says.

"And then you will lose some of your beauty, because the eighth period will never be completed, I think it's fair to say."

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