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C: Compounds

Learn about compounds, their types, how they are formed, and how to write their formulas. Understand the nomenclature system used to name different compounds.

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C: Compounds

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  1. C: Compounds • Compounds. Huh? • A compound is an electrically neutral substance that consists of two or more different elements with their atoms present in a definite ratio • Compounds: Terminology • Binary: Consists of only 2 elements • Organic: Contains Carbon and hydrogen • Inorganic: No Carbon

  2. Compounds • The atoms are bonded together due to a chemical change • The resulting compound has physical and chemical properties different than either of the reactants • Eg: Hydrogen + Oxygen = Water • Molecules: Electrically neutral compounds formed by atoms bonded together • Ions: Positive or negatively charged atom or molecule

  3. Ions • Cations: Positively charged ions • Anions: Negatively charged ions Examples

  4. Ionic and Molecular Compounds • Ionic Compound: Ions form compound that is electrically neutral • Usually formed by the reaction of a metal and a nonmetal Na(s) + Cl(g) NaCl(s) • Molecular Compound: Binary molecular compounds are usually formed by the reaction of 2 nonmetals 2H2(g) + O2(g)  2H2O (l)

  5. Formulas • Chemical (or Molecular) Formula: • The composition of a compound with chemical symbols eg: Water, Glucose • Composition only! Doesn’t give you an idea of how they are linked

  6. Formulas • Structural Formula: • Two dimensional representation of how atoms in a molecule are linked together eg: Ethanol

  7. Formulas • Line Formula: • Organic chemists sometimes omit the carbon-hydrogen bonds knowing that carbon ALWAYS forms 4 bonds eg: Ethanol

  8. Other Representations • Spacefilling model: • All atoms are spheres and the spheres are stuck together • Ball and Stick: • Atoms are balls and bonds are sticks

  9. Other Representations • Density Isosurface: • The most probable location of the electrons across entire molecule is shown • Electrostatic Potential Surface: • Show the distribution of electric charge across the density isosurface Blue----------------------------->Red Positive Negative

  10. Ionic Compounds • An ion forms when a compound gains or loses electrons • The tendency to do this will be explained in the next chapter • Ionic compounds form by the association of these positive and negative ions

  11. How do Monatomic Ions form? • In order to predict what type of ion an element will form, we need to look at the s and p blocks

  12. s block Element Ionization • Elements in the s block will lose one or two electrons depending on their group • Group 1 elements form monovalent cations • Group 2 elements form divalent cations

  13. p block Element Ionization • Elements in the p block will gain 1 to 3 electrons depending on their group • Take the group number of the element and subtract 18 from it

  14. Rule: Atoms gain or lose electrons until they have the same number as the nearest noble gas element

  15. Polyatomic Ions • Ions consisting of two or more atoms bonded together eg: Cyanide Ammonium Carbonate Nitrate Sulfate

  16. Common Ions You MUST know

  17. Ionic Compounds • In ionic compounds, the ions aren’t bonded together like they are in molecular compounds • They are associated by electric charge interactions • The chemical formulae of ionic compounds are referring to the Ratios of anions to cations • eg: NaCl : 1 Na+ for every Cl- • eg: Na2CO3: 2 Na+ for every CO32- • We need to remember the polyatomic ions to help us identify which compounds are molecular and which are ionic

  18. How do we write the formula of an ionic compound? • Step 1: Find the charge of the anion and the charge of the cation • Step 2: Combine the ions in a ratio that negates the charges • Example: Sodium chloride • Example: Aluminum Oxide

  19. D: The Nomenclature of Compounds Common Name: Historic name that gives no identity of the composition eg: Water, bleach Systematic Name: Scientific name that reveals the composition of the compound (and sometimes its structure) eg: Dihydrogen oxide, sodium hypochlorite

  20. Cations Common Name: For atoms with more than one oxidation state (transition metals) Add -ous to the lower charge state name Add -ic to the higher charge state name Cu+1: Cuprous ion Fe+2: Ferrous ion Cu+2: Cupric ion Fe+3: Ferric ion Scientific Name: Use the element name followed by Roman numerals matching the charge state (What are the scientific names of the ions above?)

  21. Anions Monatomic ions are named by adding the suffix ‘-ide’ to the stem of the element’s name (see Fluoride, chloride, oxide, bromide, sulfide above).

  22. Anions • Oxoanions can exist as multiple species, and as such, require memorization • One species of oxoanion: Add the suffix ‘-ate’ to the stem of the name Carbonate, CO32- • Two species of oxoanion: Add the suffix ‘-ite’ to the stem of the species with the lower number of oxygens AND add the suffix ‘-ate’ to the stem of the species with the higher number of oxygen atoms. Nitrite, NO2- Nitrate, NO3- Sulfite, SO32- Sulfate, SO42-

  23. Anions • Oxoanions can exist as multiple species, and as such, require memorization • Four species of oxoanion: Add ‘hypo-’ to the ‘ite’ for of the name for the species with the lowest number of oxygen atoms Add ‘per-’ to the ‘-ate’ form of the name for the species with the highest number of oxygen atoms Hypochlorite, ClO- Chlorite, ClO2- Chlorate, ClO3- Perchlorate, ClO4-

  24. Anions Oxoanions can exist as multiple species, and as such, require memorization Anions with hydrogen: Add hydrogen to the monatomic anion name HS-, Hydrogen sulfide HCO3-, hydrogen carbonate H2PO4-, Dihydrogen phosphate

  25. Naming Ionic Compounds • Ionic compounds are named by starting with the name of the cation (and oxidation number if more than one is possible), followed by the name of the anion • Hydrates are named by adding the word ‘hydrate’ preceded by the Greek prefix indicating the number of water molecules in the formula unit • Step 1: Identify the cation and the anion • Step 2: Identify the charge of the cation by looking at the anion • Step 3: Name the cation (include the oxidation number learned in step 2) • Step 4: Add the anion name

  26. Naming Ionic Compounds Examples: NaCl CoCl3 MgCl2•6H2O Fe2(SO4)3

  27. Naming Inorganic Compounds (NOT Hydrocarbons!!!) Name the element on the left and then add the number and name of the element on the right adding the suffix ‘ide’ to the stem of the element name PCl3 = Phosphorous trichloride SF6 = Sulfur hexafluoride N2O = Dinitrogen oxide N2O5 = Dinitrogen pentoxide

  28. Naming Inorganic Compounds (NOT Hydrocarbons!!!) Exceptions!!! Phosphorous compounds because it can have multiple oxidation states Common compounds: NH3 = Ammonia N2O = Nitrous oxide N2H4 = Hydrazide H2O = Water

  29. Summary of Naming Inorganic Compounds Example: Write the formula of chromium (III) nitrate hexahydrate Example: Write the formula of dinitrogen tetraoxide Example: What is the systematic name of HNO2

  30. Names of Common Organic Compounds • The names of organic compounds are based upon the names of the parent compounds above • Alcohols contain -OH groups • Carboxylic acids contain -COOH groups • Haloalkanes contane halogens

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