Chapter 2 PPt

Chapter 2 PPt - Chapter 2: Compounds and Chemical Reactions...

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1 Chapter 2: Compounds and Chemical Reactions • Essentially all elements combine to form compounds • Compounds are of two types: – Molecular, which involve shared electrons and consist of electrically neutral, discrete particles called molecules – Ionic compounds, which involve electron transfer and charged particles called ions Chemical formulas are collections of chemical symbols that are used to describe elements and compounds – Free elements are not combined with other elements in a compound • Examples: Fe (iron), Na (sodium), and K (potassium) – Many nonmetals occur as diatomic molecules • Chemical formulas specify the composition of a substance • NaCl is composed of the elements sodium and chlorine in a one-to-one (atom) ratio •Fe 2 O 3 is composed of the elements iron and oxygen in a two-to-three ratio • CO(NH 2 ) 2 expands to CON 2 H 4 , but there are good reasons to write some compounds with parentheses • Hydrates are crystals that contain water molecules, for example plaster: CaSO 4 •2H 2 O – When all the water is removed (by heating), the solid that remains is said to be anhydrous (without water)
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2 Chemical equations describe what happens in a chemical reactions • Hydrogen and oxygen combine to form water • Hydrogen and oxygen are called reactants • Water is called the product • Reactants are separated from products with “ Æ 2 H 2 + O 2 Æ 2 H 2 O • Note that the “ Æ ” is like an equal sign because both sides of the equation have the same number of each type of atom • This can be represented as: Note: Mass is conserved because the number of atoms of each type remains the same on each side of the arrow. (Both sides of the arrow show 4 H and 2 O atoms.) This equation is said to be balanced . The “2” in front of formulas H 2 and H 2 O are called coefficients . They indicate the number of molecules of each type and can change when balancing a chemical equation. The “2” in the formulas H 2 and H 2 O indicate atom ratios for the compound and must not change. • It is sometimes useful to include the physical state of reactants and products • For solids use s, liquids use l, gases use g, and for aqueous solutions use aq.
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This note was uploaded on 01/12/2012 for the course CHEM 103 taught by Professor Jeffashley during the Fall '10 term at Philadelphia.

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Chapter 2 PPt - Chapter 2: Compounds and Chemical Reactions...

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