addition reactions. Compare unsaturated. 2. (of a solution) Containing
the maximum equilibrium amount
of solute at a given temperature. In a
saturated solution the dissolved substance is in equilibrium with undissolved substance; i.e. the rate at
which solute particles leave the solution is exactly balanced by the rate at
which they dissolve. A solution containing less than the equilibrium
amount is said to be unsaturated.
One containing more than the equilibrium amount is supersaturated.
Supersaturated solutions can be
made by slowly cooling a saturated
solution. Such solutions are metastable; if a small crystal seed is added
the excess solute crystallizes out of
solution. 3. (of a vapour) See vapour
pressure.
saturation See supersaturation.
saturation spectroscopy A spectroscopic technique using lasers to locate absorption maxima with great
precision. In saturation spectroscopy
the laser beam is split into an intense
saturating beam and a less intense
beam that pass through the cavity
containing the sample in almost opposite directions. The saturating
beam sometimes excites molecules,
which are shifted to its frequency by
the Doppler effect. The other beam
gives a modulated signal at the detector if it is interacting with the same
Doppler-shifted molecules. These
molecules are not moving parallel to
the beams and have an extremely
small Doppler shift, thus providing
very high resolution. See also lamb-dip
spectroscopy.
sawhorse projection A type
of *projection in which a threedimensional view is drawn. See conformation.
s-block elements The elements of
the Ürst two groups of the *periodic
table; i.e. groups 1 (Li, Na, K, Rb, Cs,
Fr) and 2 (Be, Mg, Ca, Sr, Ba, Ra). The
outer electronic conÜgurations of
these elements all have inert-gas
structures plus outer ns
1 (group 1) or
ns
2 (group 2) electrons. The term thus
excludes elements with incomplete
inner d-levels (transition metals) or
with incomplete inner f-levels (lanthanoids and actinoids) even though
these often have outer ns
2 or occasionally ns
1 conÜgurations. Typically,
the s-block elements are reactive
metals forming stable ionic compounds containing M
+ or M
2+ ions.
See alkali metals; alkaline-earth
metals.
sc Synclinal. See torsion angle.
scandium Symbol Sc. A rare soft
silvery metallic element belonging to
group 3 (formerly IIIA) of the periodic table; a.n. 21; r.a.m. 44.956; r.d.
2.989 (alpha form), 3.19 (beta form);
m.p. 1541°C; b.p. 2831°C. Scandium
often occurs in *lanthanoid ores,
from which it can be separated on account of the greater solubility of its
thiocyanate in ether. The only natural isotope, which is not radioactive,
is scandium–45, and there are nine
radioactive isotopes, all with relatively short half-lives. Because of the
metal’s high reactivity and high cost
no substantial uses have been found
for either the metal or its compounds. Predicted in 1869 by Dmitri
*Mendeleev, and then called ekaboron, the oxide (called scandia) was
isolated by Lars Nilson (1840–99) in
1879.
A
• Information from the WebElements site
scanning electron microscope
See electron microscope.
scanning tunnelling microscope
(STM) A type of electron microscope
that uses the quantum-mechanical
*tunnel effect to study atomic struc473
scanning tunnelling microscope
s
www.AzShimi.ir www.AzShimi.com
the maximum equilibrium amount
of solute at a given temperature. In a
saturated solution the dissolved substance is in equilibrium with undissolved substance; i.e. the rate at
which solute particles leave the solution is exactly balanced by the rate at
which they dissolve. A solution containing less than the equilibrium
amount is said to be unsaturated.
One containing more than the equilibrium amount is supersaturated.
Supersaturated solutions can be
made by slowly cooling a saturated
solution. Such solutions are metastable; if a small crystal seed is added
the excess solute crystallizes out of
solution. 3. (of a vapour) See vapour
pressure.
saturation See supersaturation.
saturation spectroscopy A spectroscopic technique using lasers to locate absorption maxima with great
precision. In saturation spectroscopy
the laser beam is split into an intense
saturating beam and a less intense
beam that pass through the cavity
containing the sample in almost opposite directions. The saturating
beam sometimes excites molecules,
which are shifted to its frequency by
the Doppler effect. The other beam
gives a modulated signal at the detector if it is interacting with the same
Doppler-shifted molecules. These
molecules are not moving parallel to
the beams and have an extremely
small Doppler shift, thus providing
very high resolution. See also lamb-dip
spectroscopy.
sawhorse projection A type
of *projection in which a threedimensional view is drawn. See conformation.
s-block elements The elements of
the Ürst two groups of the *periodic
table; i.e. groups 1 (Li, Na, K, Rb, Cs,
Fr) and 2 (Be, Mg, Ca, Sr, Ba, Ra). The
outer electronic conÜgurations of
these elements all have inert-gas
structures plus outer ns
1 (group 1) or
ns
2 (group 2) electrons. The term thus
excludes elements with incomplete
inner d-levels (transition metals) or
with incomplete inner f-levels (lanthanoids and actinoids) even though
these often have outer ns
2 or occasionally ns
1 conÜgurations. Typically,
the s-block elements are reactive
metals forming stable ionic compounds containing M
+ or M
2+ ions.
See alkali metals; alkaline-earth
metals.
sc Synclinal. See torsion angle.
scandium Symbol Sc. A rare soft
silvery metallic element belonging to
group 3 (formerly IIIA) of the periodic table; a.n. 21; r.a.m. 44.956; r.d.
2.989 (alpha form), 3.19 (beta form);
m.p. 1541°C; b.p. 2831°C. Scandium
often occurs in *lanthanoid ores,
from which it can be separated on account of the greater solubility of its
thiocyanate in ether. The only natural isotope, which is not radioactive,
is scandium–45, and there are nine
radioactive isotopes, all with relatively short half-lives. Because of the
metal’s high reactivity and high cost
no substantial uses have been found
for either the metal or its compounds. Predicted in 1869 by Dmitri
*Mendeleev, and then called ekaboron, the oxide (called scandia) was
isolated by Lars Nilson (1840–99) in
1879.
A
• Information from the WebElements site
scanning electron microscope
See electron microscope.
scanning tunnelling microscope
(STM) A type of electron microscope
that uses the quantum-mechanical
*tunnel effect to study atomic struc473
scanning tunnelling microscope
s
www.AzShimi.ir www.AzShimi.com