History of the Periodic Table

History of the Periodic Table

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: • Ge, Br, K, Se • 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: • Mg, Ba, Ca, Be • F, Be, N,C

Electronegativity • Electronegativity: An atoms ability to attract electrons

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

History of the Periodic Table