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Alpha Decay
Alpha decay is one process that unstable atoms can use to become
more stable. During
alpha decay, an atom'snucleussheds two protons and two neutrons
in a packet that
scientists call analpha particle.
Since an atom loses two protons during alpha decay, it changes
from one element to
another. For example, after undergoing alpha decay, an atom
ofuranium(with 92 protons)
becomes an atom ofthorium(with 90 protons).
Alpha Particle
Produced duringalpha decay,an alpha particle is a fast
movinghelium nucleus.Alpha
particles carry a charge of +2 and strongly interact with
matter. They travel only a few inches
through air and can easily be stopped with a sheet of paper.
Beta Decay
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Beta decay is one process that unstable atoms can use to become
more stable. There are two
types of beta decay, beta-minus and beta-plus.
During beta-minus decay, aneutronin an atom'snucleusturns into
aproton,anelectronand
anantineutrino.The electron and antineutrino fly away from the
nucleus, which now has one
more proton than it started with. Since an atom gains a proton
during beta-minus decay, it
changes from one element to another. For example, after
undergoing beta-minus decay, an
atom ofcarbon(with 6 protons) becomes an atom ofnitrogen(with 7
protons).
During beta-plus decay, a proton in an atom's nucleus turns into
a neutron, apositronand a
neutrino.The positron and neutrino fly away from the nucleus,
which now has one less
proton than it started with. Since an atom loses a proton during
beta-plus decay, it changes
from one element to another. For example, after undergoing
beta-plus decay, an atom of
carbon (with 6 protons) becomes an atom ofboron(with 5
protons).
Although the numbers of protons and neutrons in an atom's
nucleus change during beta decay,
the total number of particles (protons + neutrons) remains the
same.
Beta Particle
Ejected from thenucleusduringbeta decay,a beta particle is a
fast movingelectronor
positron,depending on the type on beta decay involved. Beta
particles can travel a few feet
through air and can be stopped with a few sheets of aluminum
foil.
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Electron Capture
Electron capture is one process that unstable atoms can use to
become more stable. During
electron capture, anelectronin an atom's inner shell is drawn
into thenucleuswhere it
combines with aproton,forming aneutronand aneutrino.The neutrino
is ejected from the
atom's nucleus.
Since an atom loses a proton during electron capture, it changes
from one element to another.
For example, after undergoing electron capture, an atom
ofcarbon(with 6 protons) becomesan atom ofboron(with 5
protons).
Although the numbers of protons and neutrons in an atom's
nucleus change during electron
capture, the total number of particles (protons + neutrons)
remains the same.
Electron capture is also called K-capture since the captured
electron usually comes from the
atom's K-shell.
Electron
Electrons are negatively charged particles that surround the
atom'snucleus.Electrons were
discovered by J. J. Thomson in 1897.
Particle Data
Symbol Mass Half-life Charge Spin
e- 0.511 MeV stable -1 1/2
Half-life
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The half-life describes the amount of time needed for half of a
sample of unstable atoms or
particles to undergo decay.Thallium-208, for example, decays
intolead-208 with a half-life
of 3.05 minutes. This means that half of a sample of
thallium-208 will decay into lead-208
over the course of 3.05 minutes.
Scientists cannot predict when a particular atom or particle
will decay. They only know that,on average, half of a sample will
decay during the span of one half-life.
Isotope
Atoms that have the same number ofprotonsbut different numbers
ofneutronsare called
isotopes. The elementhydrogen,for example, has three commonly
known isotopes: protium,
deuteriumandtritium.
Neutron
Neutrons are uncharged particles found within
atomicnuclei.Neutrons were discovered by
James Chadwick in 1932.
Experiments done at theStanford Linear Accelerator Centerin the
late 1960's and early
1970's showed that neutrons are made from other particles
calledquarks.Neutrons are made
from one 'up' quark and two 'down' quarks.
Particle Data
Symbol Mass Half-life Charge Spin Quark Content
n 939.6 MeV in nuclei: stable 0 1/2 udd
free: 15 minutes
Neutron Emission
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Neutron emission is one process that unstable atoms can use to
become more stable. During
neutron emission, aneutronis ejected from an atom'snucleus.
Since the number ofprotonswithin an atom doesn't change during
neutron emission, it
doesn't change from one element to another. It does, however,
become a differentisotopeof
that element. For example, after undergoing neutron emission, an
atom ofberyllium-13 (with
9 neutrons) becomes an atom of beryllium-12 (with 8
neutrons).
Nucleus
Discovered by Ernest Rutherford in 1911, the nucleus is the
central part of an atom.
Composed ofprotonsandneutrons,the nucleus contains most of an
atom's mass.
Proton
Protons are positively charged particles found within
atomicnuclei.Protons were discovered
by Ernest Rutherford in experiments conducted between the years
1911 and 1919.
Experiments done at theStanford Linear Accelerator Centerin the
late 1960's and early
1970's showed that protons are made from other particles
calledquarks.Protons are made
from two 'up' quarks and one 'down' quark.
Particle Data
Symbol Mass Half-life Charge Spin Quark Content
p 938.3 MeV >10 years +1 1/2 uud
Proton Emission
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Proton emission is one process that unstable atoms can use to
become more stable. During
proton emission, aprotonis ejected from an atom'snucleus.
Since an atom loses a proton during proton emission, it changes
from one element to another.
For example, after undergoing proton emission, an atom
ofnitrogen(with 7 protons)
becomes an atom ofcarbon(with 6 protons).
10 Most Abundant Elements in the Earth's Crust
Source: CRC Handbook of Chemistry and Physics, 77th Edition
ElementAbundance
percent by weight
Abundance
parts per million by weight
Oxygen 46.1% 461,000
Silicon 28.2% 282,000
Aluminum 8.23% 82,300
Iron 5.63% 56,300
Calcium 4.15% 41,500
Sodium 2.36% 23,600
Magnesium 2.33% 23,300
Potassium 2.09% 20,900
Titanium 0.565% 5,650
Hydrogen 0.14% 1,400
10 Most Abundant Elements in the Universe
Source: Exploring Chemical Elements and their Compounds; David
L. Heiserman, 1992
ElementAbundance
measured relative to silicon
Hydrogen 40,000
Helium 3,100
Oxygen 22
Neon 8.6
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Nitrogen 6.6
Carbon 3.5
Silicon 1
Magnesium 0.91
Iron 0.6Sulfur 0.38
10 Most Abundant Compounds in the Earth's Crust
Source: Exploring Chemical Elements and their Compounds; David
L. Heiserman, 1992
Compound FormulaAbundance
percent by weight
Abundance
parts per million by weight
Silicon dioxide SiO2 42.86% 428,600
Magnesium oxide MgO 35.07% 350,700
Ferrous oxide FeO 8.97% 89,700
Aluminum oxide Al2O3 6.99% 69,900
Calcium oxide CaO 4.37% 43,700
Sodium oxide Na2O 0.45% 4,500
Ferric oxide Fe2O3 0.36% 3,600
Titanium dioxide TiO2 0.33% 3,300
Chromic oxide Cr2O3 0.18% 1,800
Manganese dioxide MnO2 0.14% 1,400
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