Development of the Periodic Table Objectives: • 1. State the periodic law. • 2. Discuss the contributions that Dobreiner, Newlands, Mendeleev, and Moseley made to the periodic table. Key Terms: • periodic table, periodic law
Dobereiner • The periodic table is tool that chemists have developed to organize and categorize the elements found on Earth. History: • 1700s - about 30 elements known to man • 1800s - Dobereiner began classifying elements based on properties into triads • Figured out that chemicals in the middle of his triads had properties that were the average of the chemicals that surrounded it • example: (35.5 + 126.9)/2 = 81.2 From this equation he predicted that Bromine should reside between Chlorine and Iodine
Newlands • 1865 - Newlands classified the 62 known elements by mass in repeating rows of eight. Named them octaves but was not taken seriously because of the reference to music.
Mendeleev • 1869 - Mendeleev produced the first periodic table as a logical arrangement of names and properties for his chemistry students. Arranged them in columns based on similar properties. He used this arrangement to predict the existence of three new elements.
Moseley • 1913 - Moseley determined a way to predict the positive charge in the nucleus of an atom. He ultimately found that the order of increasing positive charge reflected the chemical and physical properties of the atoms in the periodic table.
Periodic Law • The periodic table is arranged by increasing atomic number in rows called periods. • There will be a repetition to their physical and chemical properties in columns called groups or families. • elements in certain regions also share similar properties • all elements to the left & below Si, Ge, Sb, & At are metals (except H) • all elements to the right of B, Si, As, Te, & Po are non-metals including H • the elements between the metals and non-metals are semimetals (metalloids)