Further discoveries in the development of Atomic Theory
1. Conservation of mass (conservation of mass –energy)
2. 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
Further discoveries in the development of Atomic Theory
1. Conservation of mass (sort of)
2. Law of definite proportions: the composition of the same pure substance always contains the same elements in the same proportion by mass.
3. 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.
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)
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
1. NaCl
sodium chloride (sodium and chlorine)2. LiF
lithium fluoride (lithium and fluorine)3. KBr
potassium bromide (potassium and bromine)4. CaO
calcium oxide (calcium and oxygen)
5. ZnS
zinc sulfide (zinc sulfide)
More Complex Compounds1. Na2O
sodium oxide
2. Ba(OH)2
barium hydroxide
3. H2S
hydrogen sulfide
4. CO
carbon monoxide
5. CO2
carbon dioxide
6. SO3
sulfur trioxide
Chemical Bonding:
Why are most elements in the periodic table found combined?
Combined elements must be more stable under enviromental conditionsWhat is the nature of the bonding found between different elements in:
1. CO, CH4, CO2?
covalent:
2. Na+Cl-, CH3CO2-1K+, Zn+2CrO4
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ionic and ionic and covalent
3. Na, Fe, Mg, Zn
metallic (a special case of covalent bonding and ionic bonding)
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.
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
One way of looking at covalent bonding:
Some examples of molecules with covalent bonding
NaCl: an example of a substance with ionic bonding
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
Common bonding exhibited by various elements in the periodic tablecolumn number in periodic table [ ]; common charge ( ) if ionic
Alkali metals [1] (+1) 1 bond with other nonmetalsAlkaline earths [2] (+2) 2 bonds with other nonmetalsMetaloids [3] (+3) 3 bonds with other nonmetals
or metalsNonmetals Group [4] 4 bondsNon-metals Group [5] (-3) 3 bonds with nonmetals or
metalsNon-metals Group [6] (-2) 2 bonds usually with metalsNon-metals Group [7] (-1) 1 bond with metal or nonmetalInert Gases Group [8] 0 bonds with anythingTransition metals (+2, + other) 2 bonds with nonmetals
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, HFMelting point (K): 273 191 196 185 90 190Boiling temperature (K): 373 213 240 281 112 293Solvent properties: ++++ + +++ ++ + +++
In the presence of water, may substances undergo substantial changes
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
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H3PO4 + H2O = H3O+ + H2PO4-
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
strong
strong
strong
strong