History of the Periodic Table

By 1860 over 60 elements had been discovered and chemists started studying their properties. Dmitri Mendeleev decided to organize the elements by their properties.

History of the Periodic Table He wrote down all the known elements and their properties on cards. He noticed that when arranged in order by increasing atomic mass they periodically repeated some properties.

History of the Periodic Table Mendeleev noticed holes in his pattern and predicted that there were other elements to be discovered and he predicted many of their properties. Other scientist thought he was crazy until scandium, germanium, and gallium were discovered matching what Mendeleev predicted. Dmitri Mendeleev is now known as the father of the periodic table.

History of the Periodic Table Later Henry Moseley, who worked with Rutherford, realized that the elements were better organized by number of protons than by mass. This changes just a few of the elements orders.

Periodic Trends

Atomic Radii Atomic radius: one half the distance between the nuclei of two identical atoms.

Put the following elements in order of size biggest to smallest: 1.Ge, Br, K, Se 2.Ar, Ne, Xe, He

Ionization Energy Ionization Energy: The energy required to remove an electron The closer to the nucleus an electron is the harder it is to remove and therefore takes more energy.

Put the following elements in order of increasing ionization energy: 1.Mg, Ba, Ca, Be 2.F, Be, N,C

Electronegativity Electronegativity: An atoms ability to attract electrons

Put the following elements in order of increasing electronegativity: 1.N, Sb, P, Bi 2.Sr, I, Sn, Te