HISTORY OF THE PERIODIC TABLE

HENNIG BRAND (in 1649)
- First to discover a new element:
Phosphorus
- An alchemist in search of the Philosopher’s
stone (an object that would turn any metal
into gold); he even tried distilling human
urine
- Through the experiment (distilled human
urine?), Brand found a glowing white rock,
known as PHOSPHORUS

In 1869- 63 elements were already discovered

JOHN NEWLANDS AND ALEXANDRE-EMILE
BÉGUYER DE CHANCOURTOIS
- Formed their own versions of periodic
tables, which were simple yet hard to read

DMITRI IVANOVICH MENDELEEV (1834 to 1907)
- a Russian born chemist; extraordinary
- first to publish modern version of the
periodic table
- his table ordered the elements by atomic
weights (molar masses)
- Ge, Ga, Sc (elements not known at the time
Mendeleev knew them)

SIR WILLIAM RAMSAY
- Added in the noble gases

HENRY MOSLEY
- Discovered a way to quantitatively find the
atomic number of an element
- Changed the order around of Mendeleev’s
table to be organized by atomic number

MANHATTAN PROJECT in 1945
- Yielded the discovery of many new
radioactive elements

GLENN T. SEABORG
- Suggested a change to the tables in the form
of an addition of the actinide and lanthanide
series at the bottom of the table
- This idea came with the discovery of
Americium and Curium and their unique
properties.
DATE and
ELEMENTS
Before 1800
(36 elements)
1800-1849
(+22 elements)
DISCOVERIES
Discoveries during and before the
age of Enlightenment
Impulse from Scientific Revolution
and Atomic theory and Industrial
Revolution
1850-1899
The age of Classifying Elements
(+23 elements) received an impulse from the
Spectrum analysis
1900-1949
Impulse from the old quantum
(13+ elements) theory, the Refinements of the
periodic table, and quantum
mechanics
1950-1999
Manhattan_Project and Particle
(15+ elements) physics issues, for atomic numbers
97 and above

DALTON’S ATOMIC THEORY
- Different kinds of atoms may be
distinguished by their relative masses
(atomic weights)

PERIODIC LAW
- Proposed by Mendeleev
- This law states that when the elements are
listed in order of increasing atomic weights,
their properties vary periodically
- Similar elements do not have similar
weights; rather corresponding properties
are observed at regular intervals
- In constructing the table (to show the
periodic law), there were not enough
elements to fill available spaces in each row
or period, thus, concluding that these
elements are yet to be discovered

Scandium (Sc), Titanium (Ti), Calcium (Ca)
- Were unknown in 1872 in order of atomic
weights
- Scandium used to Ekaboron (as Mendeleev
termed before the element’s discovery)


5,000 years ago (idea of elements)
200 years ago (it started to finally take shape
with Mendeleev’s periodic table)
Still, it continues to transform as more and more
elements are discovered
MANIFESTING VARONIUM, LUJENIUM


PAGE 92

Oxygen-18
- Natural, stable isotope
- One of the environmental isotopes
- Is important in paleoclimatology bc scientists
can use the ratio between Oxygen-18 and
Oxygen-16 in an ice core to determine the
temperature of precipitation over time
- Was also critical to the discovery of
metabolic pathways and the mechanisms of
enzymes

MILDRED COHN
- Pioneered the usage of such isotopes to act
as tracers, so researchers could follow their
path thru reactions and gain a better
understanding of what is happening
- One of her first discoveries provided insight
into the phosphorylation of glucose that
takes place in mitochondria

MASS SPECTROMETER
- An instrument used to experimentally
determine the occurrence and natural
abundances of isotopes
1) The sample is vaporized and exposed to
a high-energy electron beam that causes
the sample’s atoms (or molecules) to
become electrically charged, typically by
losing one or more electrons
2) These cations then pass through a
(variable) electric or magnetic field that
deflects each cation’s path to an extent
that depends on both its mass and
charge
(similar to how the path of a large steel
ball rolling past a magnet is deflected to
a lesser extent than that of a small steel
ball)
3) Ions are detected, and a plot of the
relative number of ions generated
versus their mass-to-charge ratios (a
mass spectrum) is made
MASS SPECTROMETRY (MS)
- Widely used in chemistry, forensics,
medicine, environmental science, etc.
- To help identify the substances in a sample
of material
- Has evolved to become a powerful tool for
chemical analysis in a wide range of
applications