Organizing the Elements The Periodic Table

Early Greeks Four classical elements: earth, water, wind, and fire. Correspond with solid, liquid, gas, and plasma.

Elements A few elements have been known for thousands of years: copper, silver, and gold. Only 13 elements were discovered by the year 1700. When chemists started using the scientific method, the rate increased to finding 5 new elements in 10 years. Chemists needed a way to organize the elements- used the properties of the elements to sort them into groups.

J.W. Dobereiner (1780-1849) German Chemist Published a classification system where elements were put into triads. A triad is a group of 3 elements with similar properties. An example of on such triad is chlorine, bromine, and iodine.

Chlorine, Bromine, and Iodine Liquid Bromine Chlorine Gas Iodine

Chlorine, Bromine and Iodine Look different or have different physical properties. Have similar chemical properties. -all react easily with metals. The average atomic masses of chlorine and iodine is 81.177 amu. This is close to bromine which is in the middle of the other two.

Dmitri Mendeleev Russian chemist in 1869 who published a chart of elements Arranged the elements in order of increasing atomic mass

Mendeleev’s Periodic Table Mendeleev put question marks where he predicted elements should be. He predicted their properties as well as their position on the periodic table.

Henry Moseley 1913, determined an atomic number for each element Helped arrange the periodic table in order of increasing atomic number.

Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

Summary Questions What are the 4 classical elements? (early greeks) Who was the first to try and arrange a periodic table? How did Mendeleev’s periodic table differ from the modern periodic table? What did Henry Moseley contribute to the periodic table?