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Atoms, Molecules, and Ions

Atoms, Molecules, and Ions. Chapter 2. 2.6 Molecules, Compounds, and Formulas. A molecule is the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of the substance. Molecules, Compounds, and Formulas.

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Atoms, Molecules, and Ions

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  1. Atoms, Molecules, and Ions Chapter 2

  2. 2.6 Molecules, Compounds, and Formulas • A molecule is the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of the substance.

  3. Molecules, Compounds, and Formulas • How do molecules differ from their composite elements? • molecular formula • gives composition (ex. Ethanol C2H6O) • condensed formula • elements are written as groups (CH3CH2OH) • structural formula • shows how elements are attached

  4. Molecular Models • ball and stick model • space filling model

  5. 2.7 Ionic Compounds: Formulas, Names, and Properties • ionic compounds consist of charged atoms, or ions • cations and anions • metals generally lose electrons • nonmetals generally gain electrons

  6. Ions • monatomic – How can you determine charge? • Group A elements have predictable patterns of behavior, but Group B elements do not! • polyatomic ions • see chart p 74 in book – MEMORIZE!!

  7. Ionic Formulas and Names • cation is written first followed by the anion; use parentheses if more than one polyatomic ion is present • name of the metal plus the word “cation” • Ba+2 is barium cation • if metal can form more than one ion, then use Roman numerals to indicate the charge • Hg+ is mercury (I)

  8. Ionic Formulas and Names • the ending on an anion is changed to –ide • F- is fluoride (halide ions) • polyatomic ions keep their ending • SO4-2 is sulfate (oxoanions) • prefixes tell how much oxygen is present • Chlorine oxoanions are good examples!

  9. Properties of Ionic Compounds • electrostatic forces hold ions together • force of attraction or repulsion between ions is Coulomb’s law • The force between two charged particles is proportional to the magnitude of the charges (attraction between ions increases as ion charge increases) • The force is inversely proportional to the square of the distance (attraction decreases as distance between the ions increases).

  10. Properties of Ionic Compounds • ionic compounds are three dimensional arrays of atoms called a crystal lattice • high melting points due to the great attraction between ions

  11. 2.8 Molecular Compounds: Formulas, Names, and Properties • can be gases, liquids, or solids • The first nonmetal is named, the second is named with an –ide ending. • HCl hydrogen chloride • The number of atoms of a given type is indicated by using a prefix. • N2O dinitrogen monoxide • Some have common names • CH4 methane

  12. 2.9 Atoms, Molecules, and the Mole • The mole is the chemical unit measuring amount of substance. • 1 mole = 6.0221415 x 1023 particles • Avogadro’s number • molar mass is the mass in grams of one mole of an element (g/mol)

  13. Atoms, Molecules, and the Mole • use the formula of a compound to determine the molar mass • use molar mass to convert to moles (amount) • use molar mass to convert to molecules

  14. 2.10 Describing Compound Formulas • Molecular composition • formula of compound • mass of each element per mole of compound • mass of each element relative to the total mass of the compound (mass percent)

  15. Empirical and Molecular Formulas • convert mass percent to mass • convert mass of each element to moles • find the mole ratio of elements • the simplest, whole-number ratio is the empirical formula • If the molar mass is determined experimentally, then you can also figure out the molecular formula.

  16. Practice Problems • The empirical formula of acetic acid is CH2O. If its molar mass is 60.05 g/mol, what is the molecular formula of acetic acid? • Isoprene is a liquid compound that can be polymerized to form synthetic rubber. It is composed of 88.17% carbon and 11.83% hydrogen. Its molar mass is 68.11 g/mol. What are its empirical and molecular formulas?

  17. Practice Problems • Camphor is found in “camphor wood,” much prized for its wonderful odor. It is composed of 78.90% carbon and 10.59% hydrogen. The remainder is oxygen. What is its empirical formula? • Analysis shows that 0.586 g of potassium metal combines with 0.480 g of O2 gas to give a white solid having a formula of KxOy. What is the empirical formula of the compound?

  18. Hydrated Compounds • Compounds in which molecules of water are associated with the ions of the compound are called hydrated compounds. • Copper (II) chloride dihydrate is CuCl2∙2H2O which is the same as CuCl2(H2O)2 • anhydrous means a substance without water

  19. Homework for Chapter 2 • After reading sections 2.6 – 2.11, you should be able to do the following problems… • P. 107 (112-121)

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