Elements and Compounds

What element was discovered first?

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2009-06-13 06:51:52

People have known about some chemical elements such as gold,

silver, and copper from antiquity, as these can all be discovered

in nature in native form and are relatively simple to mine with

primitive tools. However, the notion that there were a limited

number of elements from which everything was composed originated

with the Greek philosopher Aristotle. Aristotle proposed that there

were four main elements: air, fire, earth and water. All of these

elements could be reacted to create another one; e.g., earth and

fire combined to form lava. However, this theory was dismissed when

the real chemical elements started being discovered. Scientists

needed an easily accessible, well organized database with which

information about the elements could be recorded and accessed. This

was to be known as the periodic table.

Hennig Brand was the first person recorded to have discovered a

new element. Brand was a bankrupt German merchant who was trying to

discover the Philosopher's Stone - a mythical object that was

supposed to turn inexpensive base metals into gold. He experimented

with distilling human urine until in 1649 he finally obtained a

glowing white substance which he named phosphorus. He kept his

discovery secret, until 1680 when Robert Boyle rediscovered it and

it became public. This and related discoveries raised the question

of what it means for a substance to be an "element". In 1661 Boyle

defined an element as a substance that cannot be broken down into a

simpler substance by a chemical reaction. This simple definition

actually served for nearly 300 years (until the development of the

notion of subatomic particles), and even today is taught in

introductory chemistry classes.

By 1869, a total of 63 elements had been discovered. As the

number of known elements grew, scientists began to recognize

patterns in the way chemicals reacted and began to devise ways to

classify the elements. The original periodic table was created

before the discovery of subatomic particles or the formulation of

current quantum mechanical theories of atomic structure. If one

orders the elements by atomic mass, and then plots certain other

properties against atomic mass, one sees an undulation or

periodicity to these properties as a function of atomic mass. The

first to recognize these regularities was the German chemist Johann

Wolfgang Döbereiner who, in 1829, noticed a number of triads of

similar elements. One of the first triads that was put together was

that of Chlorine, Bromine, and Iodine.

In 1829 Döbereiner proposed the Law of Triads: The middle

element in the triad had atomic weight that was the average of the

other two members. The densities of some triads followed a similar

pattern. Soon other scientists found chemical relationships

extended beyond triads. Fluorine was added to Cl/Br/I group;

sulfur, oxygen, selenium and tellurium were grouped into a family;

nitrogen, phosphorus, arsenic, antimony, and bismuth were

classified as another group. Dmitri Mendeleev, a Siberian-born

Russian chemist, was the first scientist to make a periodic table

much like the one we use today. Mendeleev arranged the elements in

a table ordered by atomic weight, corresponding to relative molar

mass as defined today.

For a number of years there was a gap in the periodic table

between molybdenum (element 42) and ruthenium (element 44). Many

early researchers were eager to be the first to discover and name

the missing element; its location in the table suggested that it

should be easier to find than other undiscovered elements. It was

first thought to have been found in platinum ores in 1828. It was

given the name polinium but it turned out to be impure iridium. In

fact, the missing element was technetium, an element that was not

present naturally on Earth. It was to be the first element

discovered through synthesis. This discovery filled a gap in the

periodic table, and the fact that no stable isotopes of technetium

exist explains its natural absence on Earth (and the gap). With the

longest-lived isotope of technetium, Tc-98, having a 4.2 million

year half-life, no technetium remains from the formation of the

Earth. Only minute traces of technetium occur naturally in the

Earth's crust (as a spontaneous fission product of uranium-238 or

by neutron capture in molybdenum ores), but technetium is found

naturally in red giant stars. This would set the stage for later

synthetic discoveries.

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