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Atoms, Molecules, and Ions: The Secrets of Matter

Explore the foundations of chemistry with an overview of atoms, molecules, ions, and chemical bonds. Learn about the conservation of mass, the law of definite proportions, Dalton's atomic theory, and the structure of atoms. Discover the different types of chemical bonds and how to name chemical compounds.

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Atoms, Molecules, and Ions: The Secrets of Matter

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  1. Chapter 2 Atoms, Molecules, and Ions

  2. Matter • What accounts for matters secrets? • Atomists – Democritus • All things are made of Fire – Herclitus • Four Elements – Aristotle

  3. Conservation of Mass and Law of Definite Proportions • Robert Boyle (1627–1691): Provided evidence for the atomic nature of matter. • Element - A substance that cannot be chemically broken down further • Joseph Priestley (1733–1804):

  4. Conservation of Mass and Law of Definite Proportions • Antoine Lavoisier (1743-1794):

  5. Conservation of Mass • Law of Mass Conservation: Mass is neither created nor destroyed in chemical reactions. Hg(NO3)2 + 2 KI → HgI2 + 2KNO3 3.25g + 3.32g → 4.55g + 2.02g 6.57g = 6.57g

  6. Law of Definite Proportions • Law of Definite Proportions: In a unique compound the elements will always be found in the exact same ratio.

  7. Dalton’s Atomic Theory and the Law of Multiple Proportions • John Dalton (1766–1844): Proposed explanations for the laws of mass conservation and definite proportions. • Postulate 1: Elements are made of atoms • Postulate 2: Atoms of the same element have the same properties (including mass). Atoms of different atoms have different properties • Postulate 3: Compound are comprise of elements joined together in small whole ratios • Postulate 4: Chemical reactions only rearrange the way the atoms are combined

  8. Dalton’s Atomic Theory and the Law of Multiple Proportions • Law of Multiple Proportions: • When two elements form two different compounds, the mass ratios are related by small whole numbers.

  9. The Structure of Atoms: Electrons • Elements are composed of atoms • Compounds are composed of atoms of elements in a given ratio • What does an atom look like?

  10. The Structure of Atoms • Structure of the Atom:

  11. The Structure of Atoms • Comparison of Subatomic particles

  12. Atomic Number • # protons in an atom determines the element • atomic number (Z) - Atomic number is found on the periodic table • # electrons = # protons in a neutral atom

  13. Mass Number • mass of the atom ≈ # neutrons + # protons • Mass number = # protons + # neutrons • An element may have more than one mass # • Hydrogen, Deuterium, Tritium • Isotopes: Atoms with identical atomic numbers, but different mass numbers. • Due to different # of neutrons NOT protons

  14. Atomic Mass • Atomic Mass: A weighted average of the isotopic masses of an element’s naturally occurring isotopes. • Unit – atomic mass unit (amu)

  15. Example • Chlorine has two naturally occurring isotopes: with an abundance of 75.77% and an isotopic mass of 34.969 amu, and with an abundance of 24.23% and an isotopic mass of 36.966 amu. What is the atomic mass of chlorine?

  16. Compounds and Mixtures

  17. Chemical Bonds • 2-types of bonding are found in compounds • Ionic bond • Covalent bond

  18. Ionic Bond

  19. Molecules, Ions and Chemical Bonds • Ionic Bonding (Ionic Solids): Occur between metal and non-metal

  20. Ionic Bonds

  21. Problem • Which of the following ions occurs commonly?  • A.  N3+ • B.  S6+ • C.  O2- • D.  Ca+ • E.  Cl+

  22. Ionic Bonds

  23. Ionic Bonds • Formula for Ionic Compounds – Ions combine to form neutral compounds • Examples: • Na+ and Cl– combine to form NaCl. • Ca2+ and Cl– combine to form CaCl2. • Al3+ and Cl– combine to form AlCl3. • Fe2+ and Cl- combine to form FeCl2.

  24. Molecules, Ions, and Chemical Bonds

  25. Naming Chemical Compounds • Naming Ionic Compounds - name the cation, then name the anion. • The positive ion (the metal or ammonium) • Single charge or ammonium – write its name • More than one possible charge • Write the elements name • Indicate the magnitude of charge as a roman numeral in parenthesis • The negative ion (non-metal or polyatomic ion) • Non-metal element - write root of element name with suffix –ide • Polyatomic – write the ions name

  26. Problem • Which one of the following combinations of names and formulas of ions is incorrect?  • A.  O2- oxide • B.  Al3+ aluminum • C.  NO3- nitrate • D.  PO43- phosphate • E.  CrO42- chromate

  27. Problem • Which one of the following combinations of names and formulas of ions is incorrect?  • A.  Ba2+ barium • B.  S2- sulfate • C.  CN- cyanide • D.  ClO4- perchlorate • E.  HCO3- bicarbonate

  28. Problem • Convert the names into formulas and the formulas into names • Sodium oxide • BaO • CoCl2 • (NH4)2S • Zinc Acetate • Chromium (VI) oxide

  29. Covalent Bond

  30. Molecules, Ions and Chemical Bonds • Covalent Bonding (Molecules): Between 2 non-metals or a non-metal and a metalloid.

  31. Covalent Bonds

  32. Naming Chemical Compounds • Naming Binary Molecular Compounds: • Identify which element is more cationlike.

  33. Naming Chemical Compounds • If cation-like element is H and anion-like element is O, S, Se, or a halogen • Name hydrogen • Name the anion-like element using root and –ide ending

  34. Naming Chemical Compounds • All other non-metal / metalloid combinations • Name the cation-like element • Name the anion-like element with root and –ide • Using prefixes indicate how many of each atom is present

  35. Covalent Compounds • Formula • Translate name of each element • Make the prefix of the element it’s subscript

  36. Problem • Convert formulas into names and names into formulas • PCl3 • Diiodine pentoxide

  37. Naming Compounds • Acids – are a special type of covalent compound • Acids are species that dissociate to form H+ cations and an anion when added to water. • Hence you will need to be told that they are aqueous compounds (aq) • Acids are typically indicated by writing the H first in the formula • Elemental symbols are typically written in alphabetical order

  38. Naming Compounds • Acids cont. • For current purposes, acids are going to be described as aqueous compounds of H combined with a group 17 element or a polyatomic ion. • H with group 17 elements or cyanide • Named as hydro + 17 element root + ic • H with all other polyatomic ions • Root of polyatomic ions ending in -ate + ic • Root of polyatomic ions ending in –ite + ous

  39. Problem • What is the name of the acid formed when HBr gas is dissolved in water?  • A.  bromic acid • B.  bromous acid • C.  hydrobromic acid • D.  hydrobromous acid • E.  hydrobromidic acid

  40. Optional Homework • Text – 2.26, 2.28, 2.29, 2.38, 2.46, 2.48, 2.50, 2.52, 2.54, 2.56, 2.58, 2.68, 2.78, 2.82, 2.84, 2.86, 2.88, 2.90, 2.96, 2.100, 2.104, 2.112 • Chapter 2 Homework – from website

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