Further discoveries in the development of Atomic Theory

1. Further discoveries in the development of Atomic Theory • Conservation of mass (conservation of mass –energy) • Law of definite proportions: the composition of the same pure substance always contains the same elements in the same proportion by mass • Example: • CH4 natural gas (odorless, tasteless, colorless) • CH4 + O2 = CO2 + H2O + heat

2. Further discoveries in the development of Atomic Theory • Conservation of mass (sort of) • Law of definite proportions: the composition of the same pure substance always contains the same elements in the same proportion by mass. • Law of multiple proportions: the same two elements can combine to form different compounds. However the ratio of the mass of one element that combines with a fixed amount of the second element is always in the ratio of whole numbers.

3. ethane 1gH/4gC ethylene 0.71g H/4.29gB; How much combines with 1 g of H? 0.71g H/4.29g C = 1g H/x C; x C = 6.0g benzene 0.39g H/4.61g C; How much combines with 1 g of H? 0.39g H/4.61g C = 1g H/xg C; xg C = 12 g The amount of carbon that combines with 1 g of hydrogen is in the ratio of whole numbers: 2:3:6 (or equivalently, 4: 6: 12)

4. Naming Chemical Compounds • The metal is named first followed by the name of the non metal; An alternative way of looking at this is the cation (+) is named before the anion (-) • Binary Compounds • NaCl • sodium chloride (sodium and chlorine) • LiF • lithium fluoride (lithium and fluorine) • KBr • potassium bromide (potassium and bromine) • CaO • calcium oxide (calcium and oxygen) • 5. ZnS • zinc sulfide (zinc sulfide)

6. More Complex Compounds • Na2O • sodium oxide • 2. Ba(OH)2 • barium hydroxide • 3. H2S • hydrogen sulfide • 4. CO • carbon monoxide • CO2 • carbon dioxide • 6. SO3 • sulfur trioxide

8. Chemical Bonding: • Why are most elements in the periodic table found combined? • Combined elements must be more stable under enviromental conditions • What is the nature of the bonding found between different elements in: • CO, CH4, CO2? • covalent: • 2. Na+Cl-, CH3CO2-1K+, Zn+2CrO4-2 • ionic and ionic and covalent • 3. Na, Fe, Mg, Zn • metallic (a special case of covalent bonding and ionic bonding)

9. What do we mean by these terms: ionic, metallic and covalent? • Covalent bonding: bonding between two or more elements by mutual sharing of electrons, but not necessarily equally. • Ionic bonding: bonding that occurs as a result of transfer of an electron from one element to another. This type of bonding is generally observed only in the solid state and in very polar liquids such as water. In the gas phase, bonding is generally more the result of electron sharing. • Bonding in metals: Bonding in metals is more difficult to describe but does involve sharing of electrons. In metals it is more difficult to associate specific electrons as belonging to a particular element.

10. 1. Why do different elements need to form different types of bonds? Not all elements readily form bonds. The inert gases are found in nature uncombined. Since these elements have differing number of protons and more importantly, different number of electrons surrounding the nucleus, a study of how the electrons are distributed in space may give us a clue as to why these elements (the inert gases) are un-reactive and also why other element are reactive. However we will defer this discussion until later

11. One way of looking at covalent bonding:

12. Some examples of molecules with covalent bonding

13. NaCl: an example of a substance with ionic bonding

14. Despite the fact that metals form stable bonds with each other, this doesn’t mean that they cannot be unreactive toward other substances. Take for example Al and I2 CCA3 D:\MOVIES\METALI1 Chapter 1 visuals

15. Common bonding exhibited by various elements in the periodic table column number in periodic table [ ]; common charge ( ) if ionic Alkali metals [1] (+1) 1 bond with other nonmetals Alkaline earths [2] (+2) 2 bonds with other nonmetals Metaloids [3] (+3) 3 bonds with other nonmetals or metals Nonmetals Group [4] 4 bonds Non-metals Group [5] (-3) 3 bonds with nonmetals or metals Non-metals Group [6] (-2) 2 bonds usually with metals Non-metals Group [7] (-1) 1 bond with metal or nonmetal Inert Gases Group [8] 0 bonds with anything Transition metals (+2, + other) 2 bonds with nonmetals

16. Water: H2O Water is probably the most unique and anomalous chemical substance in the universe. Without it life would not be possible. Our bodies are approximately 70 % H2O. The properties of water are anomalous in comparison to similar compounds formed by other elements. H2O H2S, NH3, PH3, CH4, HF Melting point (K): 273 191 196 185 90 190 Boiling temperature (K): 373 213 240 281 112 293 Solvent properties: ++++ + +++ ++ + +++ In the presence of water, may substances undergo substantial changes

17. The Effects of H2O on Some Substances HCl (gas) covalent bonding H2SO4 (concentrated, liquid) covalent bonding H3PO4 (liquid)covalent bonding When H2O is added to any of these three compounds, the following happens: HCl + H2O = H3O+ + Cl- 2H2SO4 + 3H2O = 2H3O+ + HSO4- + SO4-2 H3PO4 + H2O = H3O+ + H2PO4-

18. Acids and Bases Acid: A substance that readily gives up a hydrogen ion (H+). Generally we refer to an acid as something that gives up a proton to water to form a hydronium ion, simply written as H3O+. Base: A substance that readily picks up or abstracts a hydrogen ion (H+). Generally we refer to a base as a substance that picks up a proton to water to form a neutral substance, often H2O. Acid + Base = Salt + Water

19. strong strong strong strong