Greetings enchanting CSers,
And now we come to the Angstrom, a little tiny thing.
Anders Jonas Angstrom, Ph.D., was born in Sweden and taught physics
and astronomy at the University of Uppsala. He anticipated Kirchhoff in
seeing that a cool gas absorbs just those wavelenghts of light it emits
when it is hot. After Kirchhoff had established spectroscopy, Angstrom
applied it to the study of the heavenly bodies. He inspected the light
of the sun and found the hydrogen line in the suns light, showing that
the sun was powered by hydrogen. In 1867 Angstrom published a map of
the spectrum, locating about a thousand lines with great care.
He did not use an arbitrary measure as Kirchhoff had, but actually
measured the wavelengths in units equal to a *ten billionth of a
meter*. This unit was officially named the Angstrom unit in 1905.
The units of measurement generally used for describing cells are
microns, millimicrons, and angstroms.
1 inch = 25.4 millimeters
1 millimeter = 1,000 microns
1 micron = 1,000 millimicrons
1 millimicron = 10 angstroms
The unaided human eye has a resolving power of about 1/10 millimeter,
or 1/254 inch. If you look at two lines that are less than 100 microns
apart they merge into a single line. To separate lines closer than this
a microscope is used. The best light microscope has a resolving power
of 0.2 micron, or 200 millimicrons, or 2,000 angstroms. The electron
microscope has a resolving power of about 5 angstroms.
A common unit for describing the sizes of atoms is the angstrom. Atoms
range from the hydrogen atom with a diameter of about 1 A to the cesium
atom with a diameter of about 5 A. The metallic radius of a metal atom
or the covalent radius of a nonmetal atom is often referred to as the
*atomic radius*. A neutral atom has a given radius and when it becomes
a positive ion its radius becomes smaller, and when it becomes a
negative ion its radius becomes larger. If energy is applied to an atom
sufficient to raise the electron orbits to the next energy level the
atomic radius becomes larger.
An atom consists of two main parts, the positively charged central
part called the *nucleus* and a negatively charged part called the
*electron* moving around the nucleus. These charges balance each other
and the atom is neutral.
The single proton that is the nucleus of the hydrogen atom has a
diameter of about 10-13 cm or 10-5 A, now thats really small. Now 10-5
A is about one-hundred-thousandth of the diameter of the atom itself
which is about 0.6A in diameter or 0.3 A radii. In other words most of
the volume of an atom is empty space.
Lets look at some other atomic radii;
H-hydrogen- 0.3 A
Cu-copper- 1.18 A
Ag-silver- 1.34 A
Au-gold- 1.34 A
O-oxygen- 0.66 A
Pt-platinum- 1.3 A
The traditional units for light wavelengths are Angstroms and
millimicrons. However the new approved SI units are *nanometers* and
are the proper units to use (by some people).
1 angstrom is = to 10-10 meter
1 millimicron is = to 10-9 meter
1 nanometer is = to 10-9 meter
As we see the old millimicron is now replaced by the nanometer, both
are 10-9 meter. Of interest is how the millimicron worked, milli was-3
and micron was -6 and when put together became -9, but now we use the
nanometer -9.
Some may remember the old term micromicro (-12) which was micro -6 and
micro -6 combined to make -12, which we now call pico (-12).
Symbols
milli --- m -3
micro --- u -6
pico --- p -12
nano --- n -9
millimicron --- mu -9
micromicro ---- uu -12
Now visible light falls in the range of 4000 to 7500 angstroms, or
from 400 to 750 nanometers (nm), (1 nanometer is 10 angstroms). The
conversion is a simple movement of one power of ten. Below (smaller)
4000 A is the UV light and above 7500 A is the IR light. Of course the
visible light is what we see, and its in colors of;
UV -- below 400 nm
violet-- 400 to 425 nm
blue -- 425 to 490 nm
green -- 490 to 560 nm
yellow -- 560 to 590 nm
orange -- 590 to 640 nm
red -- 640 to 750 nm
IR -- above 750 nm
Lets look at other interesting conversions.
1 angstrom = 10-4 micron (u) or 0.1 millimicron (mu)
To convert from angstroms to centimeters multiply by 1 X 10-8
inches 3.937 X 10-8
meters 1 X 10-10
microns 0.0001
millimicrons 0.1
Looking at atomic radii, you will find some variation in the data
from different publications This is usually because of different ways
of arriving at the data. There are data derived from empirical data and
using wave-mechanics. Here are some of them;
element empirical wave-mechanic
Ag 1.44 A 1.26 A
Ag +1 1.13 A
Au 1.44 A or 1.40 A
Au +1 1.37 A
H 0.3 A
H -1 2.08 A
O 0.6 A
O -2 1.32 A
O +6 0.09 A
Pt 1.38 A
As we see, adding or removing electrons will vary the radii quite a
bit.
If the wavelength of a given light is known then many interesting
things can be done.
Lets take a green light at 5,000 A (500 nm). The wavelength will be
0.00005 cm or 5000 A or 0.1 uu (micromicro) or 0.1 nm (nanometer).
The frequency of the green light would be 6 X 10 +14 vibrations per
sec. Thats 600,000,000,000,000 vibrations per sec. Thats 600 tera hertz
or 0.6 peta hertz.
The wave number of this green light would be 2 X 10+4 or 20,000 waves
per cm (centimeter) or 20,000 vibrations in a *length* of one cm.
If we calculate the *size of the quantum* for this green light we find
4.0 pico (micromicro) ergs of energy.
Its amazing how the angstrom gets around in science. :-)
Bless you Bob Lee
--
oozing on the muggy shore of the gulf coast
[email protected]
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