CHE_106_Lecture5_2009

CHE_106_Lecture5_2009 - Chemistry 106 Lecture 5 Topics...

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Chemistry 106 Lecture 5 Topics: Periodic Table Molecules, Ions, Compounds Chapter 2.5 – 2.9
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The Periodic Table In 1869, Dmitri Mendeleev discovered that if the known elements were arranged in order of atomic number , they could be placed in horizontal rows such that the elements in the vertical columns had similar properties.
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The Periodic Table
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Periodicity When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities .
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Periods and Groups The periodic table is a tabular arrangement of elements in rows and columns, highlighting the regular repetition of properties of the elements. A period consists of the elements in one horizontal row of the periodic table. A group consists of the elements in any one column of the periodic table. The groups are usually numbered. The eight “A” groups are called main group (or representative) elements.
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The Periodic Table Periods run horizontal (rows) cal (columns) Groups run vertic
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The Periodic Table Periods and Groups The “B” groups are called transition elements. The two rows of elements at the bottom of the table are called inner transition elements. Elements in any one group have similar properties.
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The Periodic Table The “halogens” all have similar properties Transition Elements Inner Transition Elements
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The Periodic Table Periods and Groups The elements in group 1A, often known as the alkali metals , are soft metals that react easily with water. The group 7A elements, known as the halogens, are also reactive elements. The group 8A elements, known as the noble gases, generally are non-reactive . Table 2.3
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Metals, Nonmetals, and Metalloids A metal is an element that has a luster (shine), a good conductor of heat and electricity, and often malleable and ductile . Copper and gold are examples. A nonmetal is an element that does not exhibit the characteristics of the metal. Carbon and oxygen are examples. A metalloid , or semi-metal, is an element having both metallic and nonmetallic properties. Silicon and germanium are good semiconductors .
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The Periodic Table
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Tying it all Together: Chemical Formulas The chemical formula of a substance is a notation using atomic symbols with subscripts to convey the relative proportions of atoms of the different elements in a substance. Consider the formula of aluminum oxide, Al 2 O 3 . This formula indicates that the compound is composed of aluminum atoms and oxygen atoms in the ratio 2:3.
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Molecular Substances A molecule is a definite group of atoms that are chemically bonded together – that is, tightly connected by attractive forces. A molecular substance is a substance that is composed of molecules, all of which are alike.
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