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Objectives

Objectives. To understand and illustrate the Law of Constant Composition To learn about Dalton’s theory of atoms To learn how a formula describes a compound’s composition. Dalton Intro. A given compound always contains the same proportion by mass of the elements of which it is composed.

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Objectives

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  1. Objectives • To understand and illustrate the Law of Constant Composition • To learn about Dalton’s theory of atoms • To learn how a formula describes a compound’s composition Dalton Intro

  2. A given compound always contains the same proportion by mass of the elements of which it is composed. • A mixture can have variable composition but the composition of a compound is fixed • Does this give us a clue about the nature of matter? Law of Constant Composition (1799 Joseph Louis Proust)

  3. Dalton’s Atomic Theory (John Dalton 1766-1844) • Dalton’s Atomic Theory states: • All elements are composed of atoms • All atoms of a given element are identical • Atoms of different elements are different • Compounds consist of combinations of atoms of different elements • Atoms are not created or destroyed in a chemical reaction You have 90 seconds to memorize these 5 parts of the theory!!

  4. Formulas of Compounds • A compound is represented by a chemical formula in which the number and kind of atoms present is shown by using the element symbols and subscripts. • Example: the simple sugar, glucose

  5. Put your notes away and write a set of rules for how to write a formula of a compound. Be as complete as you can be using what you have learned throughout your course

  6. B. Formulas of Compounds • Each atom present is represented by its element symbol. • The number of each type of atom is indicated by a subscript written to the right of the element symbol. • When only one atom of a given type is present, the subscript 1 is not written. • Write a metallic element first if present (MgCl2) • Write the central atom of a molecule first (PCl5) • Write Carbon first and Hydrogen second for an organic molecule (C6H12O6)

  7. Formulas of compounds • Write the formulas for the following compounds: • A phosphorus atom bonded to three chlorine atoms • A molecule containing two boron atoms and six hydrogen atoms • A compound containing one calcium atom for every two chlorine atoms • Four hydrogen atoms bonded to a single carbon atom • A compound containing two iron atoms for every three oxygen atoms • A molecule of aspirin (acetylsalicylic acid – four oxygen atoms, eight hydrogen, nine carbon atoms)

  8. Aspirin, acetylsalicylic acid, C9H8O4 Aspirin in Motion Element Hangman

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