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Understanding Elements, Compounds & Properties in Chemistry

Learn about elements as fundamental substances with unique properties, diatomic and triatomic elements, compounds formed by chemical combinations, particle diagrams, pure substances vs. mixtures, laws of chemistry, and proportions in compounds.

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Understanding Elements, Compounds & Properties in Chemistry

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  1. Elements & Compounds

  2. Elements • Substances that cannot be broken down or decomposed into simpler substances by any means. • Definite properties. • Formulas have 1 uppercase letter.

  3. Atom • The smallest particle of an element that • retains the properties of the element. • can undergo a chemical reaction.

  4. Diatomic & Triatomic Elements • Some elements occur as molecules, not atoms. Describe the following: He N2 O3 S8 Ar Cl2

  5. Diatomic Molecules • Memorize the following: • H2 • N2 • O2 • F2 • Cl2 • Br2 • I2

  6. Compounds • 2 or more different elements chemically combined in a definite ratio. • Properties of compounds are different from those of the elements from which they are formed.

  7. source Source 2Na + Cl2 2NaCl Unique Properties source

  8. Compounds • Homogeneous. • Broken into elements by a chemical decomposition reaction. • Formulas have 2 or more uppercase letters.

  9. Particle Diagrams • Each kind of circle represents a different element. • Circles that are touching are chemically combined.

  10. Particle Diagrams Atoms of a monatomic element.         Molecules of a diatomic element.        

  11. Particle Diagrams Pure substance: units the same. molecules of a triatomic compound.          Mixture: units differ. monatomic element, diatomic element, triatomic compound.             

  12. Mixture vs. Pure Substance:The Scheme of Things!

  13. Phys. M. Chem. Mixtures  Separated by physical methods. Compounds  Separated by chemical methods.

  14. Law of Definite Proportions • A given compound always has the same elements in the same proportions by mass. • A definite recipe!

  15. Percent by Mass  = Part X 100% Whole Part = mass of each element Whole = mass of compound

  16. Law of Multiple Proportions • Same elements can make more than 1 compound – different recipes! • H2O : 2 parts H to 1 part O • H2O2 : 2 parts H to 2 parts O • So H2O2 has twice as much O as H2O. • The different masses of O that can combine with a fixed mass of H are related by small whole numbers.

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