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.

As time progressed…

The Developmental History of the Periodic Table The development of the periodic table begins with German chemist Johann Dobereiner ( ) who grouped elements based on similaritiesJohann Dobereiner 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 ( )John Newlands 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 ( ) proposed arranging elements by atomic weights and properties.Dimitri Mendeleev

Dmitri Mendeleev

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