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.
2.
3.
4.
5.
NaCl
sodium chloride
(sodium and chlorine)
lithium fluoride
(lithium and fluorine)
potassium bromide
(potassium and bromine)
calcium oxide
(calcium and oxygen)
zinc sulfide
(zinc sulfide)
LiF
KBr
CaO
ZnS
More Complex Compounds
1.
Na2O
sodium oxide
2.
Ba(OH)2
barium hydroxide
3.
H2 S
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 conditions
What is the nature of the bonding found between different elements in:
1. 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)
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 table
column number in periodic table [ ]; common charge ( ) if ionic
Alkali metals
Alkaline earths
Metaloids
[1] (+1)
[2] (+2)
[3] (+3)
Nonmetals Group [4]
Non-metals Group [5] (-3)
Non-metals Group [6] (-2)
Non-metals Group [7] (-1)
Inert Gases Group [8]
Transition metals (+2, + other)
1 bond with other nonmetals
2 bonds with other nonmetals
3 bonds with other nonmetals
or metals
4 bonds
3 bonds with nonmetals or
metals
2 bonds usually with metals
1 bond with metal or nonmetal
0 bonds with anything
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, 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
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-
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