Basic Chemistry

(Valence = number of potential bonds formed by an atom of that type. For elements in Groups Ia, IIa, IIIb, and IVb, Valence = Group #. For elements in Groups Vb through VIII, valence = 8 - Group #)

I. Important Elements

Group 1: Those which form complex molecules
Name	Symbol	Valence
Hydrogen	H	1
Oxygen	O	2
Nitrogen	N	3
Carbon	C	4
Sulfur	S	2
Phosphorus	P	5
Group 2: Those which maintain electrochemical properties or regulate diffusion
Name	Symbol	Valence
Sodium	Na	1
Potassium	K	1
Magnesium	Mg	2
Calcium	Ca	2
Chlorine	Cl	1
Fluorine	F	1
Iodine	I	1
Group 3: Enzyme Activators
Name	Symbol	Valence
Iron	Fe	2*
Copper	Cu	2*
Cobalt	Co	2*
Zinc	Zn	2
Molybdenum	Mo	2

*Varies, with oxidation state

II. Atoms are joined by chemical bonds

• Covalent bonds involve the sharing of electrons between atoms which have roughly equal capacities to attract electrons, as in hydrogen gas (H-H), or methane (CH₄). Covalent bonds are characteristically formed by atoms in groups which are relatively adjacent to each other on the periodic chart.

Increasing electronegativity

As the distance between groups increases, the difference in electronegativity of the elements increases, so that the bond becomes

• H₂O, or water

  Polar, in which there is a partial positive charge at one end of the molecule and a partial negative charge at the other. Examples include ammonia (NH₃) and water (H₂O).

When the atoms are at the extreme opposite sides of the periodic chart, as in Groups Ia and VIIb, the atoms are not electrically neutral. This leads to

• NaCl, sodium chloride, aka table salt.

  Ionic bonds, in which an atom will gain or lose one or more electrons. Positively charged ions are termed cations and negatively charged ions are called anions.

III. Hydrogen bonds are weak attractive forces between the positively charged hydrogen atom of one molecule to the negatively charged atom of another.

• Accounts for thermal properties of water

• Explains strong attractive forces binding two strands of DNA

IV. Acids are proton donors; bases are proton acceptors.

• Water molecules tend to dissociate into OH- ions and H+ ions. The measure of pH = -[log] H+ ions.
• pH of 7 is neutral, <7 is acidic, >7 is alkaline.