Periodic Table Flashcards
Who developed the periodic table
Johan Doberiener
Dobereiner’s Law of Triads
- The development of the periodic table begins with
German chemist Johann Dobereiner (1780-1849)
who grouped elements based on similarities. - Dobereiner noticed the same pattern for the alkali metal
triad (Li/Na/K) and the halogen triad (Cl/Br/I). - In 1829 Dobereiner proposed the Law of Triads: Middle
element in the triad had atomic weight that was the
average of the other two members.
Newlands’ Law of Octaves
- John Newlands, an English chemist,
wrote a paper in 1863 which classified
the 56 established elements into 11
groups based on similar physical
properties, noting that many pairs of
similar elements existed which differed
by some multiple of eight in atomic
weight. - In 1864 Newlands published his version
of the periodic table and proposed the
Law of Octaves (by analogy with the
seven intervals of the musical scale). This
law stated that any given element will
exhibit analogous behaviour to the eighth
element following it in the table.
Mendeleev’s Periodic Table
- Dimitri Mendeleev (1860s)
arranged known elements in a
table, according to atomic mass - properties of elements repeated
in a pattern of regular intervals
(periodically) - left gaps in table wherever there
was a break in properties - table could be used to predict
physical and chemical properties
of unknown elements based on
properties of known elements –
made Mendeleev famous!
Henry Moseley and Atomic Numbers
- Henry Moseley published the results of
his measurements of the wavelengths of
the x-ray spectral lines of a number of
elements which showed that the
ordering of the wavelengths of the x-ray
emissions of the elements coincided
with the ordering of the elements by
atomic number. - With the discovery of isotopes of the
elements, it became apparent that
atomic weight was not the significant
player in the periodic law as Mendeleev,
Meyers and others had proposed. - The properties of the elements varied
periodically with atomic number.
Modern Periodic Table
- arranges elements according to increasing
atomic number (number of protons)
natural elements
– atomic number 1 to 92
– exist naturally on Earth
synthetic/man made elements
– have been made by scientists
– atomic number greater than 93
to 116
synthetic element
(number 112)
produced from the
fusion
eg.Ununbium is a
Classes of Elements in the Periodic
Table
metals (left side)
nonmetals (right side)
metalloids (along diagonal “staircase” line)
METAL Properties
- hard
- shiny
- malleable
- ductile
- good conductor (of heat and electricity)
- solid (except mercury, which is a liquid)
NONMETAL Properties
- not shiny
- not malleable
- not ductile
- dull
- brittle
- poor conductor (of heat and electricity)
- some gases, some solids (except bromine,
which is a liquid)
METALLOID Properties
- shares some properties with metals and some
properties with nonmetals - possibly shiny
- solid
- brittle
- silicon and germanium are semi-conductors
what is Boron used for (B)
Boron: Used as an insecticide
and used for killing rodents.
What is sliicon used for (Si)
Silicon: Used in making
computer chips.
what is germanuim used for ( Ge)
Germanium: First electronic
semi-conductor.
