tute for Heavy Ion Research where it
was Ürst produced.
A
• Information from the WebElements site
date-rape drugs Drugs that are
used to render the victim unable to
resist a sexual assault. Particular
drugs used for this purpose are Ûunitrazepam and gammahydroxybutyric
acid (GHB).
dating techniques Methods of estimating the age of rocks, palaeontological specimens, archaeological
sites, etc. Relative dating techniques
date specimens in relation to one another; for example, stratigraphy is
used to establish the succession of
fossils. Absolute (or chronometric)
techniques give an absolute estimate
of the age and fall into two main
groups. The Ürst depends on the existence of something that develops at a
seasonally varying rate, as in dendrochronology and varve dating. The
other uses some measurable change
that occurs at a known rate, as in
*chemical dating, radioactive (or radiometric) dating (see carbon dating;
fission-track dating; potassium–
argon dating; rubidium–strontium
dating; uranium–lead dating),
*amino acid racemization, and *thermoluminescence.
dative bond See chemical bond.
daughter 1. A nuclide produced by
radioactive *decay of some other nuclide (the parent). 2. An ion or free
radical produced by dissociation or
reaction of a parent ion or radical.
Davisson–Germer experiment
See electron diffraction.
Davy, Sir Humphry (1778–1829)
British chemist, who studied gases at
the Pneumatic Institute in Bristol,
where he discovered the anaesthetic
properties of *dinitrogen oxide (nitrous oxide). He moved to the Royal
Institution, London, in 1801 and Üve
years later isolated potassium and
sodium by electrolysis. He also prepared barium, boron, calcium, and
strontium as well as proving that
chlorine and iodine are elements. In
1816 he invented the *Davy lamp.
Davy lamp An oil-burning miner’s
safety lamp invented by Sir Humphry
Davy in 1816 when investigating
Üredamp (methane) explosions in
coal mines. The lamp has a metal
gauze surrounding the Ûame, which
cools the hot gases by conduction
and prevents ignition of gas outside
the gauze. If Üredamp is present it
burns within the gauze cage, and
lamps of this type are still used for
testing for gas.
d-block elements The block of elements in the *periodic table consisting of scandium, yttrium, and
lanthanum together with the three
periods of transition elements: titanium to zinc, zirconium to cadmium,
and hafnium to mercury. These elements all have two outer s-electrons
and have d-electrons in their penultimate shell; i.e. an outer electron
conÜguration of the form (n–1)d
x
ns
2 ,
where x is 1 to 10. See also transition
elements.
DDT Dichlorodiphenyltrichloroethane; a colourless organic crystalline compound, (ClC 6 H 4 ) 2 CH(CCl 3 ),
made by the reaction of trichloromethanal with chlorobenzene. DDT
is the best known of a number of
chlorine-containing *pesticides used
extensively in agriculture in the
1940s and 1950s. The compound is
stable, accumulates in the soil, and
concentrates in fatty tissue, reaching
dangerous levels in carnivores high
in the food chain. Restrictions are
now placed on the use of DDT and
similar pesticides.
deacetylation The removal of an
date-rape drugs
162
d
www.AzShimi.ir www.AzShimi.com
was Ürst produced.
A
• Information from the WebElements site
date-rape drugs Drugs that are
used to render the victim unable to
resist a sexual assault. Particular
drugs used for this purpose are Ûunitrazepam and gammahydroxybutyric
acid (GHB).
dating techniques Methods of estimating the age of rocks, palaeontological specimens, archaeological
sites, etc. Relative dating techniques
date specimens in relation to one another; for example, stratigraphy is
used to establish the succession of
fossils. Absolute (or chronometric)
techniques give an absolute estimate
of the age and fall into two main
groups. The Ürst depends on the existence of something that develops at a
seasonally varying rate, as in dendrochronology and varve dating. The
other uses some measurable change
that occurs at a known rate, as in
*chemical dating, radioactive (or radiometric) dating (see carbon dating;
fission-track dating; potassium–
argon dating; rubidium–strontium
dating; uranium–lead dating),
*amino acid racemization, and *thermoluminescence.
dative bond See chemical bond.
daughter 1. A nuclide produced by
radioactive *decay of some other nuclide (the parent). 2. An ion or free
radical produced by dissociation or
reaction of a parent ion or radical.
Davisson–Germer experiment
See electron diffraction.
Davy, Sir Humphry (1778–1829)
British chemist, who studied gases at
the Pneumatic Institute in Bristol,
where he discovered the anaesthetic
properties of *dinitrogen oxide (nitrous oxide). He moved to the Royal
Institution, London, in 1801 and Üve
years later isolated potassium and
sodium by electrolysis. He also prepared barium, boron, calcium, and
strontium as well as proving that
chlorine and iodine are elements. In
1816 he invented the *Davy lamp.
Davy lamp An oil-burning miner’s
safety lamp invented by Sir Humphry
Davy in 1816 when investigating
Üredamp (methane) explosions in
coal mines. The lamp has a metal
gauze surrounding the Ûame, which
cools the hot gases by conduction
and prevents ignition of gas outside
the gauze. If Üredamp is present it
burns within the gauze cage, and
lamps of this type are still used for
testing for gas.
d-block elements The block of elements in the *periodic table consisting of scandium, yttrium, and
lanthanum together with the three
periods of transition elements: titanium to zinc, zirconium to cadmium,
and hafnium to mercury. These elements all have two outer s-electrons
and have d-electrons in their penultimate shell; i.e. an outer electron
conÜguration of the form (n–1)d
x
ns
2 ,
where x is 1 to 10. See also transition
elements.
DDT Dichlorodiphenyltrichloroethane; a colourless organic crystalline compound, (ClC 6 H 4 ) 2 CH(CCl 3 ),
made by the reaction of trichloromethanal with chlorobenzene. DDT
is the best known of a number of
chlorine-containing *pesticides used
extensively in agriculture in the
1940s and 1950s. The compound is
stable, accumulates in the soil, and
concentrates in fatty tissue, reaching
dangerous levels in carnivores high
in the food chain. Restrictions are
now placed on the use of DDT and
similar pesticides.
deacetylation The removal of an
date-rape drugs
162
d
www.AzShimi.ir www.AzShimi.com