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Copy of Chapter 6.1 Development of the Modern Periodic Table
Transcript of Copy of Chapter 6.1 Development of the Modern Periodic Table
columns called groups
rows called periods The 1800s brought a large increase in the number of known elements. Some scientists who contributed to the periodic table... John Newlands Meyer
Mendeleev Moseley Late 1700s: French scientist who complied a list of all elements that were known at the time. The list consisted of 33 elements organized in 4 categories. He noticed that when the elements were arranged by increasing atomic mass, their properties repeated every 8th element. A pattern such as this is called periodic because it repeats in a specific manner. Newlands proposed an organizational scheme for the elements. Both Meyer and Mendeleev demonstrated a connection between atomic mass and elemental properties. By arranging the elements in order of increasing atomic mass into columns with similar properties, Mendeleev organized the elements into a periodic table. Mendeleev is given more credit because he published his work first. Mendeleev's table became widely accepted because he predicted the existence and properties of undiscovered elements that were later found. He left blanks in the table and by noting trends in the properties of known elements, he was able to predict the properties of the yet-to-be-discovered elements. Mendeleev's table, however was not completely correct. After new elements were discovered and the atomic masses of the known elements were more accurately determined, it became apparent that several elements in the table were not in the correct order. Arranging the elements by mass resulted in several elements being placed in groups they did not belong. Moseley discovered that by arranging the elements in order of increasing atomic number the problems with the order of the elements were solved. Moseley's arrangment resulted in a clear periodic pattern of properties. The statement that there is a periodic repetition of chemical and physical properties of the elements when they are arranged by increasing atomic number is called the periodic law. There are 7 periods and 18 groups. Elements is groups 1, 2, and 13-18 possess a wide range of chemical and physical properties. For this reason, they are referred to as the representative elements. The elements in groups 3-12 are referred to as the transition elements. Most metals are also malleable and ductile, meaning that they can be pounded into thin sheets and drawn into wire. Most representative elements and all transition elements are metals. If you look at boron, in column 13, you will see a stairstep line that zigzags down to astatine. This stairstep line is a visual divider between metals and the nonmetals on the table. Group 1 metals (except for hydrogen) are known as alkali metals (highly reactive). Group 2 metals are known as alkaline earth metals (highly reactive). The transition metals are divided into transition metals and inner transition metals. Groups 3-12 make up the transition metals. Inner transition metals are made up of the lanthanide series and actinide series. (the f sublevel elements) Nonmetals Nonmetals occupy the upper right side of the periodic table. Nonmetals are elements that are generally gases or brittle, dull-looking solids. They are poor conductors of heat and electricity. Group 17 is highly reactive elements that are known as halogens. Group 18 is the extremely unreactive elements commonly called noble gases. Metalloids have physical and chemical properties of both metals and nonmetals. This introduction to the periodic table touches only the surface of its usefulness. DONE BY THE ISKA