Atomic Theory

• Further developments

1. Conservation of mass (conservation of mass –energy)

Further 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); always CH4

CH4 + O2 = CO2 + H2O + heat

Further 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.

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?

1g H/xg C = 0.71g H/4.29g C ; x C = 6.0g

benzene 0.39g H/4.61g C; How much combines with 1 g of H?

1g H/x C = 0.39g H/4.61g C; x 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 CompoundsThe 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 (-)

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) NaCl;KBr mov

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 environmental conditionsWhat 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 Br2MF Ch6-09; AlBr3.mov

1

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

icebomb