- Group III elements are B, Al, Ga, In, and Tl. Their
outer electron configuration is s 2 p1. - Group IV contains the elements C, Si, Ge, Sn, and
Pb. Their outer electron configuration is s 2 p2. - Group V contains the elements N, P, As, Sb, and Bi.
Their outer electron configuration is s 2 p3. - Group VI (chalcogens) are the elements O, S, Se, Te,
and Po. Their outer electron configuration is s 2 p4. - Group VII (halogens) are the elements F, Cl, Br, I,
and At. Their outer electron configuration is s 2 p5. - Group VIII (inert gases or noble gases) are the ele-
ments He, Ne, Ar, Kr, Xe, and Rn. Their outer elec-
tron configuration is s 2 p6.
PCR SeePOLYMERASE CHAIN REACTION.
peptide bond The bond that links amino acids
together. Created by a condensation reaction between
the alpha-amino group of one amino acid and the alpha-
carboxyl group of another amino acid; a covalent bond.
peptidoglycan A thick, rigid-layer, cross-linked
polysaccharide-peptide complex that is found in the
walls of bacteria. Composed of an overlapping lattice
of two sugars, N-acetyl glucosamine (NAG) and N-
acetyl muramic acid (NAM), that are cross-linked by
amino-acid bridges found only in the cell walls of bac-
teria. This elaborate, covalently cross-linked structure
provides great strength of the cell wall.
peptidomimetic A compound, containing nonpep-
tidic structural elements, that is capable of mimicking
or antagonizing the biological action of a natural par-
ent peptide. A peptidomimetic no longer has classical
peptide characteristics such as enzymatically scissille
peptidic bonds.
See alsoPEPTOID.
peptoid A PEPTIDOMIMETIC that results from the
oligomeric assembly of N-substituted glycines.
percentage ionization The percentage of the weak
electrolyte that ionizes in a solution of given concen-
tration.
percent by mass The actual yield divided by theoret-
ical yield multiplied by 100 percent. Number of grams
of solute dissolved in 100 g of solution.percent composition The relative measure of the
mass of each different element present in the compound.percent ionic character Ionic character refers to the
amount of time that a bond exists in the ionic form,
which is measured by the percent of ionic character. The
numerical value of the percent of ionic character is
related to the difference in electronegativity values for
the two bonded atoms. If the difference is greater than
1.7, then the bond is ionic. If the difference is between
1.7 and 0.3, then the bond is polar covalent. If the dif-
ference is below 0.3, then the bond is nonpolar covalent.percent purity The percent of a specified compound
or element found in an impure sample.perfect gas(ideal gas) A gas with molecules with no
size that exhibits no intermolecular forces and that
obeys the ideal gas equation relating pressure, volume,
and temperature; PV = nRT, where R is a constant and
n is the number of moles of gas. Real gases can approx-
imate the behavior of an ideal gas at low pressure.perfluorocarbon(PFC) A derivative of hydrocar-
bons in which all of the hydrogens have been replaced
by fluorine. They are clear, colorless, odorless, noncon-
ducting, and nonflammable liquids that are nearly
twice as dense as water, and they are capable of dis-
solving large amounts of physiologically important
gases (oxygen and carbon dioxide). PFCs are generally
very chemically stable compounds that are not metabo-
lized in body tissues. They are used in paints to make
them spread easier, in textile manufacturing as a fabric
protectant, as radiological imaging agents, and they
have been explored as blood substitutes. Their vapors
are also potent greenhouse gases.pericyclic reaction A CHEMICAL REACTIONin which
concerted reorganization of bonding takes placepericyclic reaction 209