Please summarize the contributions of the following people in the development of the atomic model:

(you may use your book)

• Demokritos and Leucippos• John Dalton• J.J. thomson• Robert Milikan• Ernest Rutherford

Also, draw the shorthand form for C-14, C-16 and C-18.

Periodic table of Elements

As time progressed…

The Developmental History of the Periodic Table

• The development of the periodic table begins with German chemist Johann Dobereiner (1780-1849) who grouped elements based on similarities

• 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

Continued…

• Defects of Triad Classification: – A large number of similar elements could not be grouped

into triads e.g., iron, manganese, nickel, cobalt, zinc and copper are similar elements but could not be placed in the triads.

– It was possible that quite dissimilar elements could be grouped into triads.

Newlands’ Octaves• English chemist John Newlands (1837-1898)• After an interval of eight elements similar physical / chemical

properties reappeared. • Newlands was the first to formulate the concept of periodicity

in the properties of the chemical elements.• In 1863 he proposed the Law of Octaves: Elements exhibit

similar behavior to the eighth element following it in the table.

Continued…

• Defects of Law of Octaves:– This law could be best applied, only up to the element

calcium.– Newly discovered elements could not fit into the octave

structure.– The feature of resemblance of the 8th element when

arranged in increasing order of their atomic mass was not successful with heavier elements.

The Father of the Modern Periodic Table

Then in 1869, Russian chemist Dimitri Mendeleev (1834-1907) proposed arranging elements by atomic weights and properties.

Dmitri Mendeleev

Periodic table of Elements

Periodic Law: When the elements are arranged in order of increasing atomic number, there is a periodic repetition of their

physical and chemical properties

Metals

• High electrical conductivity

• Ductile (able to be cut and drawn into wires)

• High luster (Shiny) when clean

• Malleable (able to be beaten into thin sheets)

• Solid at room temperature (with one exception)

Non-Metals

• Nonlustrous (not shiny)

• Poor conductors of electricity

• If solid…Brittle

Metalloids?

• Have some properties of metals and some properties of non-metals