Physical Science 8th grade (1).pdf

Lets take a closer look at these elements sodium is

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Let’s take a closer look at these elements. Sodium is on the left side of the periodic table of elements, a metal. Its atomic number is 11. It is soft, light, and silvery-white. Sodium is highly reactive and never found in pure form in nature. It oxidizes in air and reacts violently with water. Chlorine is on the right side of the periodic table, a halogen. Its atomic number is 17. It is yellow-green in color and poisonous. Chlorine is commonly found in nature as a gas. In liquid form it is a powerful oxidizing and bleaching agent; it is a component of chlorine bleach. Chlorine combines easily with nearly all other elements. Sodium chloride is a crystal. The particular crystal structure of sodium chloride is cubic. Each sodium ion is surrounded by six chlorine ions. Each chlorine ion is surrounded by six sodium ions. This is known as the halite structure and is common to many minerals. “The salt of the Earth” is precious Sodium chloride is one of Earth’s most common compounds. It makes the oceans salty; it is found in most human tissue; it is plainly essential to life. Yet long ago, salt was one of the most valuable substances in the world. Having it was as good as money in the bank. Wars were fought over salt. We take common table salt for granted now, but salt has been uncommonly important to human civilization and to life here on Earth. Questions: 1. Compare the two chief methods of gathering salt. 2. How did salt affect the expansion of human civilization? 3. What are the differences between chlorine and sodium? 4. Describe the crystal structure of sodium chloride. Chapter 8 Connection
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174 Molecular Gumdrop Models Molecules are the structures that result when two or more atoms bond by sharing electrons. In living things, almost all molecules are made from hydrogen, carbon, nitrogen, oxygen, phosphorus, and sulfur. Molecules are described using formulas. For example, H 2 is a molecule consisting of two hydrogen atoms. CH 4 is a molecule consisting of one carbon atom and four hydrogen atoms. In this activity, you will build some simple molecules out of gumdrops and toothpicks. Materials: Toothpicks White, red, yellow and green gumdrops What you will do 1. Colored gumdrops will represent the atoms you use to build your molecules: white (or brown) gumdrops represent nitrogen, red gumdrops represent carbon, yellow gumdrops represent hydrogen, and green gumdrops represent oxygen. Toothpicks will represent each bond in your model. Remember that hydrogen can have one bond, oxygen can have two bonds, carbon can make four bonds and nitrogen can have three bonds. The bonding between two atoms can be single, double or triple. So, carbon could make its four bonds with four single bonds, or two double bonds, or one double bond and two single bonds, or one single bond and one triple bond.
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