Y
yeasts A group of unicellular fungi
of the class Hemiascomycetae and
phylum Ascomycota. They occur as
single cells or as groups or chains of
cells; yeasts reproduce asexually by
budding and sexually by producing
ascospores. Yeasts of the genus Saccharomyces ferment sugars and are
used in the baking and brewing industries.
ylide A chemical species derived
from an onium ion by loss of a hydron. For example, the phosphorus
ylide (C 6 H 5 ) 2 P=CR 2 , derived from
(C 6 H 5 ) 2 PCHR 2
+ by loss of H
+
.
yocto- Symbol y. A preÜx used in
the metric system to indicate 10
–24
.
For example, 10
–24 second = 1 yoctosecond (ys).
yotta- Symbol Y. A preÜx used in
the metric system to indicate 10
24 .
For example, 10
24 metres = 1 yottametre (Ym).
ytterbium Symbol Yb. A silvery
metallic element belonging to the
*lanthanoids; a.n. 70; r.a.m. 173.04;
r.d. 6.965 (20°C); m.p. 819°C; b.p.
1194°C. It occurs in gadolinite, monazite, and xenotime. There are seven
natural isotopes and ten artiÜcial isotopes are known. It is used in certain
steels. The element was discovered
by Jean de Marignac (1817–94) in
1878.
A
• Information from the WebElements site
yttrium Symbol Y. A silvery-grey
metallic element belonging to group
3 (formerly IIIA) of the periodic table;
a.n. 39; r.a.m. 88.905; r.d. 4.469
(20°C); m.p. 1522°C; b.p. 3338°C. It
occurs in uranium ores and in *lanthanoid ores, from which it can be
extracted by an ion exchange
process. The natural isotope is yttrium–89, and there are 14 known artiÜcial isotopes. The metal is used in
superconducting alloys and in alloys
for strong permanent magnets (in
both cases, with cobalt). The oxide
(Y 2 O 3 ) is used in colour-television
phosphors, neodymium-doped lasers,
and microwave components. Chemically it resembles the lanthanoids,
forming ionic compounds containing
Y
3+ ions. The metal is stable in air
below 400°C. It was discovered in
1828 by Friedrich Wöhler.
A
• Information from the WebElements site
www.AzShimi.ir www.AzShimi.com
yeasts A group of unicellular fungi
of the class Hemiascomycetae and
phylum Ascomycota. They occur as
single cells or as groups or chains of
cells; yeasts reproduce asexually by
budding and sexually by producing
ascospores. Yeasts of the genus Saccharomyces ferment sugars and are
used in the baking and brewing industries.
ylide A chemical species derived
from an onium ion by loss of a hydron. For example, the phosphorus
ylide (C 6 H 5 ) 2 P=CR 2 , derived from
(C 6 H 5 ) 2 PCHR 2
+ by loss of H
+
.
yocto- Symbol y. A preÜx used in
the metric system to indicate 10
–24
.
For example, 10
–24 second = 1 yoctosecond (ys).
yotta- Symbol Y. A preÜx used in
the metric system to indicate 10
24 .
For example, 10
24 metres = 1 yottametre (Ym).
ytterbium Symbol Yb. A silvery
metallic element belonging to the
*lanthanoids; a.n. 70; r.a.m. 173.04;
r.d. 6.965 (20°C); m.p. 819°C; b.p.
1194°C. It occurs in gadolinite, monazite, and xenotime. There are seven
natural isotopes and ten artiÜcial isotopes are known. It is used in certain
steels. The element was discovered
by Jean de Marignac (1817–94) in
1878.
A
• Information from the WebElements site
yttrium Symbol Y. A silvery-grey
metallic element belonging to group
3 (formerly IIIA) of the periodic table;
a.n. 39; r.a.m. 88.905; r.d. 4.469
(20°C); m.p. 1522°C; b.p. 3338°C. It
occurs in uranium ores and in *lanthanoid ores, from which it can be
extracted by an ion exchange
process. The natural isotope is yttrium–89, and there are 14 known artiÜcial isotopes. The metal is used in
superconducting alloys and in alloys
for strong permanent magnets (in
both cases, with cobalt). The oxide
(Y 2 O 3 ) is used in colour-television
phosphors, neodymium-doped lasers,
and microwave components. Chemically it resembles the lanthanoids,
forming ionic compounds containing
Y
3+ ions. The metal is stable in air
below 400°C. It was discovered in
1828 by Friedrich Wöhler.
A
• Information from the WebElements site
www.AzShimi.ir www.AzShimi.com