IONS, ACIDS, BASES, AND pH
Ions: Ion's can be monoatomic or polyatomic. Monoatomic ions result when an atom loses (metal ions)
or gains (non-metal ions) one or more electrons. When metal atoms lose an electron, the protons then
outnumber the electrons and the resulting ion is positively charged.
Metal ions important in biological systems include:
Na+, K+, Mg++, Ca++
When atoms of non-metals gain an electron, the resulting ion will have a negative charge.
Non-metal, monoatomic ions in biological systems include:
F-, ClIonic bonds form between a positive metal ion and a negative non-metal ion.
Covalent bonds form between non-metals, and there are several very important polyatomic ions that are
covalently bonded, but which form ionic bonds to either hydrogen, ammonium, or a metal. Important
examples of polyatomic ions in biology include:

Nitrate
NO3Nitric Acid = H(NO3)
Phosphate
PO4-3
Phosphoric Acid = H3(PO4)
Hydroxide
OH
Sulfate
SO4-2
Sulfuric Acid = H2(SO4)
+
Ammonium NH4
Carbonate
CO3-2
Carbonic Acid = H2(CO3)
NOTE: The examples above are but a fraction of those that are known to exist, but are among the
most important in biology. You should also note that those with the suffix "ate" are all acidic.
Acids, Bases and pH
Hydrogen ions are critical in a number of biological processes. HYDROGEN ION = PROTON. An
acid is any compound (solid, liquid, or gas) that results in the dissociation of hydrogen ions in water.
Proton pumps in the lining of your stomach maintain a strongly acidic environment to aid in digestion and
eliminate potential pathogens. Proton pumps are also critical components of energy systems in cells,
including photosynthesis and cellular respiration.
Hydroxide ions: You may have noticed that a hydrogen ion and a hydroxide ion can combine to form a
water molecule, however, water is not an ionically bonded molecule, but rather a polar covalent molecule.
A base is any compound (solid, liquid, or gas) that results in the dissociation of hydroxide ions in water.
At any given instant a certain proportion of water molecules have dissociated to H+ ions and OH- ions.
The pH of an aqueous solution is measured in terms of the inverse log (-log) of the concentration of H+.
Because the pH value is an inverse relationship, the lower the pH value, the higher the concentration of
H+, and therefore the greater the acidity. In pure water, the H+ concentration measured as the negative
log is 7.0. The pH scale ranges from 0 (extremely acidic) to 14 (extremely basic). A solution with a pH
of 7.0 is neutral (neither acid or base).