The document summarizes the development of the periodic table over time by various scientists from the 17th century to today. Dmitri Mendeleev produced one of the first recognizable periodic tables in 1869, arranging elements based on atomic weight and leaving gaps for undiscovered elements. Later, Henry Moseley determined that arranging elements by atomic number instead of weight gave a better organization, and scientists like Glenn Seaborg continued discovering new elements that were added to the table. The periodic table is now a fundamental tool that organizes all the known elements according to their atomic structure.

1. DEVELOPMENT OF THE
PERIODIC TABLE

2. Although elements such as gold, silver,
tin, copper, lead and mercury have been
known since earliest times, the first
scientific discovery of an element
occurred in 1649. Hennig Brand, a
German alchemist, treated urine to a
series of processes that resulted in the
production of the element phosphorus.

3. Over the next 200 years, a great deal
of knowledge about elements and
compounds was gained. By the middle
of the 19th century, about 60 elements
had been discovered.

4. ALEXANDRE-EMILE
BÉGUYER DE
CHANCOURTOIS
In 1862, French geologist
Alexandre-Emile Béguyer de
Chancourtois listed the elements on
paper tape and wound them, spiral
like, around a cylinder. Certain
‘threes’ of elements with similar
properties came together down the
cylinder. He called his model the
Scientists began to recognise patterns in the
properties of these elements and set about
developing classification schemes:

5. JOHN NEWLANDS
In 1864, English chemist John
Newlands noticed that, if the
elements were arranged in
order of atomic weight, there
was a periodic similarity every 8
elements. He proposed his ‘law
of octaves’ on this.

6. LOTHAR MEYER
In 1869, Lothar Meyer complied a
periodic table of 56 elements based
on a regular repeating pattern of
physical properties such as molar
volume. Once again, the elements
were arranged in order of increasing
atomic weights.

7. DMITRI MENDELEEV
Also in 1869, Russian chemist
Dmitri Mendeleev produced a
periodic table based on atomic
weights but arranged ‘periodically’.
Elements with similar properties
appeared under each other. Gaps
were left for yet to be discovered
elements.

8. WILLIAM RAMSAY
In 1894, William Ramsay
discovered the noble gases
and realised that they
represented a new group in
the periodic table.

9. HENRY MOSELEY
In 1914, Henry Moseley determined
the atomic number of each of the
known elements. He realised that, if
the elements were arranged in order
of increasing atomic number rather
than atomic weight, they gave a
better fit within the ‘periodic table’.

10. GLENN SEABORG
In 1940, Glenn Seaborg
artificially produced heavy mass
elements such as neptunium.
These new elements were part
of a new block of the periodic
table called ‘actinides’.

11. THE PERIODIC TABLE TODAY
MOST SCHOOL SCIENCE LABORATORIES HAVE A COPY OF THE PERIODIC
TABLE PINNED TO A WALL SOMEWHERE.
CLOSE INSPECTION OF THE TABLE SHOWS THE FOLLOWING
DISTRIBUTION OF TYPES OF ELEMENT.
Most of the elements are metals. Metalloids are elements that have some of the
physical properties of metals but some of the chemical properties of non-metals.
Antimony, for example, conducts electricity but its chemistry resembles that of the
non-metal phosphorus.