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Elements & Componds

Elements & Componds. & Law of Definite Proportions. Mr. Shields Regents Chemistry U03 L06. The “Basics”. If we look at a leaf macroscopically we might describe it As green, serrated edge, smooth, containing lines etc. If we look at this leaf on smaller and even smaller scales

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Elements & Componds

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  1. Elements & Componds & Law of Definite Proportions Mr. Shields Regents Chemistry U03 L06

  2. The “Basics” If we look at a leaf macroscopically we might describe it As green, serrated edge, smooth, containing lines etc. If we look at this leaf on smaller and even smaller scales We would see that it is not just leaf but is in fact composed of very tiny units, for example: Cells DNA molecules RNA molecules Amino Acids Atoms D e c. S i z e

  3. So what is an Atom? • The smallest particle of an element that retainsthe properties of the element. • The smallest particle of an element that can undergo a chemical reaction • Atoms are NON-DIVISIBLE using ordinary chemical processes

  4. There are today 115 elements known to man. Some are present naturally and some are man made.

  5. The Periodic Table of the Elements 2 elements are Liquid 11 elements are Gases Elements 1 – 92 can be found in nature (except 2) Of these 92, 78% are metals Elements 93-115 are all manmade

  6. If atoms are single elements what do we have when We join several atoms together? COMPOUNDS ! • A Compound is defined as 2 or more different elements chemically combined in a definite ratio of atoms and mass (ex Fe2O3).

  7. Compounds • Properties of compounds are different from those • of the elements from which they are formed • They are Homogeneous (we’ll discuss this later). • Can be Broken down into elements thru chemical change decomposition (ex. 2HgO  2Hg + O2) • In the Classification of Matter (which we’ll also • discuss later) Elements and Compounds are • known as PURE SUBSTANCES

  8. Law of Definite Proportions As we’ve discussed, a compound is a substance that contains two or more different elements combined in a FIXED or CONSTANT COMPOSITION The LAW OF DEFINITE PROPORTIONS states that regardless of the amount present, a compound is always Composed of the same elements in the same proportion by mass. So what does this mean? …

  9. Law of Definite Proportions Every single spec in a pile of magnesium oxide (MgO) consists of many molecules. And each molecules has: 1 Mg atom and 1 O atom The atomic mass of Magnesium is 24.3 amu and the mass of Oxygen is 16.0 amu. Therefore, the total mass of MgO is 40.3 amu So, Mg = (24.3/40.3) x 100 = 60.3% by mass and O = (16.0/40.3) x 100 = 39.7% by mass

  10. Law of Defintie Proportions • Since the % composition of MgO is approx. 60.3% Mg and 39.7% O then ... • Then In 100g of MgO I have 60.3g of Magnesium and 39.7g of Oxygen. • This could also be stated as “the percent Composition of Oxygen in MgO is always 39.7% and the % composition of Mg in MgO is always 60.3 %”

  11. Now try this one! PROBLEM: How many grams of Magnesium and Oxygen do I have if I have 200Kg of MgO? (Mg= 60.3% and O=39.7%) In 200Kg of MgO there is approximately… 39.7% x 200Kg = 79.4Kg of Oxygen AND 60.3% x 200Kg = 120.6Kg of Magnesium

  12. Now try this one! How many pounds of Iron can I theoretically Obtain from 1 ton (2000lbs) of Fe2O3 (iron ore)? In 1 ton of Fe2O3 there is approximately… Atomic mass of Fe2O3 = (55.8x2)+(16x3)= 159.6 amu Fe = (111.6/159.6) x 100 = 69.9% of Fe2O3 69.9% of 2000lbs = 1398 lbs

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