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Elements & Compounds

Elements & Compounds. Elements. Substances that cannot be broken down or decomposed into simpler substances by any means. Definite properties. Formulas have 1 uppercase letter. Atom. The smallest particle of an element that retains the properties of the element.

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Elements & Compounds

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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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