Transcript What is the structure of an atom?

The Atom
Lab # 2
What’s Inside an Atom?
• An atom is made up of a team of three
players: protons, neutrons, and
electrons
• They each have a charge, mass, and a
location
• Protons + Neutrons collectively called
nucleons
What is the structure of an atom?
• Nucleus – center of the atom
– Home of Protons and Neutrons
–Proton
• Has a positive (+) charge
• Has a relative mass of 1
• Determines the atomic number
• Found inside the nucleus
What is the structure of an atom?
– Neutron
• Has no charge (0)
• Has a relative mass of 1
• Determines the isotope
–Isotopes are two of the same
element with different masses
• Found inside the nucleus
What is the structure of an atom?
• Electron
– Has a negative (-) charge
– Has a relative mass of 0 (zero)
– Determines the ion
– Found outside the nucleus
Electrons circle around the nucleus of an atom.
Protons are a main part of the nucleus of an atom.
Neutrons also hang out in the nucleus of an atom.
How are P, N, e- related?
• # protons = atomic number = Z
– Ex: The atomic number of Hydrogen (H) is 1, so all
have 1 proton.
• # hydrogen
electronsatoms
= # protons
in a neutral atom
– Ex: All Oxygen atoms (O) have 8 protons, so the
atomic number of Oxygen is 8.
# protonsall+ atoms
# neutrons
= massneutral.
number = A
• • Remember
are electrically
• Therefore; the number of Protons equal the number of
– Ex: Helium (He) has 2 protons and 2 neutrons: its
Electrons.
mass number is 4.
• Meaning the number of negatively charged particles
– Ex: Carbon (C) has 6 protons and 6 neutrons: its
must equal the number of postively charged particles.
mass number is12.
Structure of the Nucleus
• # protons + # neutrons = mass number = A
A
Z
X
•# protons = atomic number = Z
N
•# neutrons
Structure of the Nucleus
27
A
13
Al
14
Decay of Radionuclides
• Some 3000 nuclides have been discovered
and most are unstable.
• Unstable nuclei decay by one of the following
in order to achieve stability
– spontaneous fission
– α-particle
– β-particle
– σ-ray emission
– Electron capture
Decay of Radionuclides
• The stability of a nuclide is governed by the
structural arrangement and binding energy of
the nucleons in the nucleus.
• The ratio of the number of neutrons to the
number of protons N/Z is an approximate
index of the stability of a nuclide.
• N/Z = 1 in the stable nuclei with low atomic
no.
12
• Ex, 6 C
Decay of Radionuclides
• Radionuclides may decay by any one or a
combination of six processes:
– Spontaneous fission
– α decay
– β- decay
– β+decay
– Electron capture
– Isomeric transition
Decay of Radionuclides
• Radionuclides may decay by any one or a combination of
six processes:
– Spontaneous fission
•Fission is a process in which a heavy nucleus breaks down
into two fragments typically in the ratio of 60:40.
•This process is accompanied by the emission of
•Two or three neutrons with a mean energy of 1.5 MeV.
•A release of 200 MeV energy appears mostly as heat.
•Fission in heavy nuclei can occur spontaneously or by
bombardment with energetic particles.
•Spontaneous fission is an alternative to a decay or g
emission
Decay of Radionuclides
• Radionuclides may decay by any one or a
combination of six processes:
– α decay
•Usually heavy nuclei decay by α particle emission.
•The α particle is a helium ion containing two protons and two
neutrons bound together in the nucleus.
•In α particle the atomic number of the parent nuclide is therefore
reduced by 2 and the mass number by 4.
•An example of a decay is
Decay of Radionuclides
• Radionuclides may decay by any one or a
combination of six processes:
– β- decay
•When a nucleus is ‘‘neutron rich’’ it decays by β- particle
emission along with an antineutrino.
•An antineutrino is an entity almost without mass and charge
(i.e., has a higher N/Z ratio compared to the stable nucleus)
and is primarily needed to conserve energy in the decay.
•In β- decay, a neutron essentially decays into a proton (p) and
a β- particle
•For example
Decay of Radionuclides
• Radionuclides may decay by any one or a
combination of six processes:
– β- decay
Decay of Radionuclides
• Radionuclides may decay by any one or a
combination of six processes:
– Positron or β+decay
•Nuclei that are ‘‘neutron deficient’’ or ‘‘proton rich’’ can decay by
β+ particle emission accompanied by the emission of a neutrino
(i.e.,
have an N/Z ratio less than that of the stable nuclei)
which is an opposite entity of the antineutrino.
•After β+ particle emission, the daughter nuclide has an atomic
number that is 1 less than that of the parent.
•In β+ decay, a proton transforms into a neutron by emitting a
β+ particle and a neutrino
•For example,
Decay of Radionuclides
• Radionuclides may decay by any one or a
combination of six processes:
– β+ decay
Decay of Radionuclides
• Radionuclides may decay by any one or a
combination of six processes:
– Electron capture
•Electron is captured from the extranuclear electron shells.
•Thus, transforming a proton into a neutron and emitting a
neutrino.
Decay of Radionuclides
• Radionuclides may decay by any one or a
combination of six processes:
– Isomeric transition
•The decay of an upper excited state
to a lower excited state
•A nucleus can remain in several
excited energy states above the
ground state.
•All these excited states are referred
to as isomeric states and decay to the
ground state
Nomenclature
• Isotopes:
• Nuclides of the same atomic number.15 O 16 O 17O
8
8
8
• Isotones:
• Nuclides having the same number of neutrons but different atomic
number
•
59
Fe
26
60 Co
27
62Cu
29
• Isobars:
• Nuclides with the same no. of nucleons that is the same mass no. but
different no. of protons
•
67Cu
29
67 Zn
30
• Isomers:
• Nuclides having the same number of protons and neutrons but differing
in energy states and spins.
99Tc 99mTc
Units of Radioactivity
• 1 curie (Ci) = 3.7 X 10 10 dps
•
= 2.22 X 10 12 dpm
• 1 millicurie (mCi) = 3.7 X 10 7 dps
•
= 2.22 X 10 9 dpm
• 1 microcurie (µCi) = 3.7 X 10 4 dps
•
= 2.22 X 10 6 dpm
Units of Radioactivity
• 1 Becquerel (Bq)= 1 dps = 2.7 X 10 -11 Curie
• 1 kilobecquerel (kBq)= 2.7 X 10 -8 Curie
• 1 Ci = 3.7 X 10 10 Becquerel (Bq)
Decay Equations
• -dN/dt=λN
– λLambda= decay constant.
– Defined as the probability of disintegration per unit time
for the radioactive atom
– -dN/dt = A =disintegration rate
– N is the no. of radioactive atoms
• At = Aoe-yt
• A=λN
• λ=0693/t1/2
– t1/2 = the time required to reduce the initial activity of a
radionuclide to one half
Problems
1. At 11:00 A.M., the 99mTc readioactivity was
measured as 9 mCi on a certain day. What
was the activity at 8:00 A.M. and 4:00 P.M.
on the same day (t1/2 of 99mTc= 6hr)
Thank You
“Instead of giving yourself
reasons why you can’t ,
give yourself reasons why
you can”