h 音标拼音: ['etʃ]
n . 字母
h 字母
h H n 1 :
a nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas ;
the simplest and lightest and most abundant element in the universe [
synonym : {
hydrogen }, {
H }, {
atomic number 1 }]
2 :
a unit of inductance in which an induced electromotive force of one volt is produced when the current is varied at the rate of one ampere per second [
synonym : {
henry }, {
H }]
3 :
the constant of proportionality relating the energy of a photon to its frequency ;
approximately 6 .
626 x 10 ^-
34 joule -
second [
synonym : {
Planck '
s constant }, {
h }]
4 :
the 8th letter of the Roman alphabet [
synonym : {
H }, {
h }]
5 : (
thermodynamics )
a thermodynamic quantity equal to the internal energy of a system plus the product of its volume and pressure ; "
enthalpy is the amount of energy in a system capable of doing mechanical work " [
synonym : {
heat content },
{
total heat }, {
enthalpy }, {
H }]
H \
H \ ([=
a ]
ch ),
the eighth letter of the English alphabet ,
is classed among the consonants ,
and is formed with the mouth organs in the same position as that of the succeeding vowel .
It is used with certain consonants to form digraphs representing sounds which are not found in the alphabet ,
as sh ,
th , [
th ],
as in shall ,
thing , [
th ]
ine (
for zh see [
sect ]
274 );
also ,
to modify the sounds of some other letters ,
as when placed after c and p ,
with the former of which it represents a compound sound like that of tsh ,
as in charm (
written also tch as in catch ),
with the latter ,
the sound of f ,
as in phase ,
phantom .
In some words ,
mostly derived or introduced from foreign languages ,
h following c and g indicates that those consonants have the hard sound before e ,
i ,
and y ,
as in chemistry ,
chiromancy ,
chyle ,
Ghent ,
Ghibelline ,
etc .;
in some others ,
ch has the sound of sh ,
as in chicane .
See Guide to Pronunciation , [
sect ][
sect ]
153 ,
179 ,
181 -
3 ,
237 -
8 .
[
1913 Webster ]
Note :
The name (
aitch )
is from the French ache ;
its form is from the Latin ,
and this from the Greek H ,
which was used as the sign of the spiritus asper (
rough breathing )
before it came to represent the long vowel ,
Gr . [
eta ].
The Greek H is from Ph [
oe ]
nician ,
the ultimate origin probably being Egyptian .
Etymologically H is most closely related to c ;
as in E .
horn ,
L .
cornu ,
Gr .
ke `
ras ;
E .
hele ,
v .
t .,
conceal ;
E .
hide ,
L .
cutis ,
Gr .
ky `
tos ;
E .
hundred ,
L .
centum ,
Gr .
"
e -
kat -
on ,
Skr . [.
c ]
ata .
[
1913 Webster ]
{
H piece } (
Mining ),
the part of a plunger pump which contains the valve .
[
1913 Webster ]
H \
H \ (
h [
aum ]). (
Mus .)
The seventh degree in the diatonic scale ,
being used by the Germans for B natural .
See {
B }.
[
1913 Webster ]
Ion \
I "
on \ ([
imac ]"[
o ^]
n ),
n . [
Gr . '
io `
n ,
neut ,
of '
iw `
n ,
p .
pr .
of '
ie `
nai to go .]
1 . (
Elec .
Chem .)
an atom or goup of atoms (
radical )
carrying an electrical charge .
It is contrasted with neutral atoms or molecules ,
and free radicals .
Certain compounds ,
such as sodium chloride ,
are composed of complementary ions in the solid (
crystalline )
as well as in solution .
Others ,
notably acids such as hydrogen chloride ,
may occur as neutral molecules in the pure liquid or gas forms ,
and ionize almost completely in dilute aqueous solutions .
In solutions (
as in water )
ions are frequently bound non -
covalently with the molecules of solvent ,
and in that case are said to be solvated .
According to the electrolytic dissociation theory ,
the molecules of electrolytes are divided into ions by water and other solvents .
An ion consists of one or more atoms and carries one unit charges of electricity ,
3 .
4 x 10 ^{-
10 }
electrostatic units ,
or a multiple of this .
Those which are positively electrified (
hydrogen and the metals )
are called {
cations };
negative ions (
hydroxyl and acidic atoms or groups )
are called {
anions }.
Note :
Thus ,
hydrochloric acid ({
HCl })
dissociates ,
in aqueous solution ,
into the hydrogen ion , {
H },
and the chlorine ion , {
Cl -};
ferric nitrate , {
Fe (
NO3 )
3 },
yields the ferric ion , {
Fe },
and nitrate ions , {
NO3 -}, {
NO3 -},
{
NO3 -}.
When a solution containing ions is made part of an electric circuit ,
the cations move toward the cathode ,
the anions toward the anode .
This movement is called migration ,
and the velocity of it differs for different kinds of ions .
If the electromotive force is sufficient ,
electrolysis ensues :
cations give up their charge at the cathode and separate in metallic form or decompose water ,
forming hydrogen and alkali ;
similarly ,
at the anode the element of the anion separates ,
or the metal of the anode is dissolved ,
or decomposition occurs .
Aluminum and chlorine are elements prepared predominantly by such electrolysis ,
and depends on dissolving compounds in a solvent where the element forms ions .
Electrolysis is also used in refining other metals ,
such as copper and silver .
Cf .
{
Anion }, {
Cation }.
[
Webster 1913 Suppl .]
2 .
One of the small electrified particles into which the molecules of a gas are broken up under the action of the electric current ,
of ultraviolet and certain other rays ,
and of high temperatures .
To the properties and behavior of ions the phenomena of the electric discharge through rarefied gases and many other important effects are ascribed .
At low pressures the negative ions appear to be electrons ;
the positive ions ,
atoms minus an electron .
At ordinary pressures each ion seems to include also a number of attached molecules .
Ions may be formed in a gas in various ways .
[
Webster 1913 Suppl .]
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