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Understanding Atoms, Molecules, and Ions: Key Historical Developments and Chemical Laws

This chapter delves into the evolution of atomic theory from ancient Greek philosophy to the 1600s and beyond. Highlighting key figures like Boyle and the advancements made in the 1800s, it explores fundamental chemical laws, including the Law of Conservation of Mass, the Law of Definite Proportions, and the Law of Multiple Proportions. These laws illustrate how elements combine to form compounds in fixed proportions, using water and carbon dioxide as pivotal examples. The chapter also presents problems for applications of these laws, promoting a deeper understanding of chemical interactions.

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Understanding Atoms, Molecules, and Ions: Key Historical Developments and Chemical Laws

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  1. Chapter 2 Atoms, Molecules, and Ions

  2. History • Greeks, BC • AD, Alchemy, beginning of element disc. • 1600’s Boyle, gases • 1800’s more scientists, more laws developed and more elements discovered

  3. Fundamental Chemical Laws • Law of Conservation of Mass • Mass cannot be created or destroyed but can be changed from one form to another

  4. Law of Definite Proportions • A given compound always contains exactly the same proportions of elements by mass • Take H2O, water. There is no other way to make water. It must always be 2 Hydrogen atoms and one Oxygen atom. • Or 1.008 g H to 16.00 g of O • 1 : 15.87 proportion of H:O by mass

  5. Carbon and Oxygen • CO is always 1 g carbon to 1.33g oxygen (12.0 g 60 16.00g) • CO2 is always 1 g carbon to 2.66 g oxygen

  6. Think of Any Other Compound? • Law of Definite Proportions applies • MgO (24.31 : 16.00 or 1 : 0.6581) • NaCl • KBr • H2O2

  7. Law of Multiple Proportions • When two elements form a series of compounds, the ratio of the masses of the second element that combine with 1 g of the first element can always be reduced to small whole numbers

  8. Example N and O • The amount of N that combines with O is • Compound A, N2O, 2 N : 1 O • Compound B, NO, 1 N : 1 O • Compound C, NO2, 1 N : 2 O • All obey the Law of Definite Proportions

  9. Problems • You react 100 g Compound A with 20 g Compound B to make one product. What is the mass of the product? • A. 10 g B. 100 g C. 120 g D. > 120 g

  10. 3 A + B ---- C + D • If you react 4 moles A with 2 moles B what products (moles of C, D) would you get.

  11. What is the difference between the Law of Definite Proportions and the Law of Multiple Proportions?

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