Transcript 1. Nucleons Protons and neutrons 2. Nuclide A atom in

1.
Nucleons
Protons and neutrons
2.
Nuclide
A atom in nuclear chemistry.
Identified by the number of
protons and neutrons -mass
number.
3. Ways to identify nuclides:
a. 228
Ra
88
b. Radium -228
4. Mass Defect and Nuclear Stability
The difference between the mass of an atom
and the sum of the masses of its protons,
neutrons and electrons.
5. Example:
Helium-4
2 protons (2 x 1.007276) = 2.014552amu
2 neutrons(2x1.008665) = 2.017330amu
2 electrons(2x.0005486) = .001097amu
total mass = 4.032979amu
The measured mass = 4.00260amu
Mass defect = 4.032979-4.00260=.03038amu
6. Nuclear Binding Energy
Convert mass to Kg to match units for energy
Kg X meters(squared) / seconds(squared)
1amu = 1.660540 X 10 -27 Kg
.03038amu = 5.0446 x 10 -29 Kg
E = mc2
E=(5.0446 x 10 -29Kg) (3.00 X 10 8m/s)2
E = 4.54 x 10-12 Kg x m2/s2 = 4.54 x 10-12 J
Nuclear Binding Energy = 4.54 x 10-12 J
Nuclear binding Energy
The energy released when a nucleus is
formed from nucleons. Can also be
thought of as the amount of energy
needed to break apart a nucleus.
Therefore, the nuclear binding energy is a
measure of the stability of a nucleus.
7. Binding Energy per Nucleon
The binding energy of the nucleus
divided by the number of nucleons it
contains
Use pages 701-702
1. Calculate the nuclear binding energy of a Sulfur–
32 atom. The measured atomic mass of Sulfur–32 is
31.972070 amu.
2. Calculate the nuclear binding energy of a Oxygen-16
atom. The measured atomic mass of Oxygen-16 is
15.994915 amu.
3. Calculate the binding energy per nucleon of a
Manganese-55 atom. Measured atomic mass is
54.938047amu.
8. Nucleons and Nuclear Stability
Band of Stability – stable nuclei clusters over
a range of neutron-proton ratios
Radioactive Decay
Spontaneous disintegration of
a nucleus with emission of particles
and/or electromagnetic radiation
(nuclear radiation)
Radioactive Nuclide
unstable nucleus
Types of Radioactive Decay
1. Alpha particles
a. Helium -4
b. Both number of neutrons
and protons must decrease
to stabilize.
• Beta emission- instability in elements
above the band of stability occurs
because the nucleus has too many
neutrons. To decrease the number of
neutrons, a neutron can be converted
into a proton and an electron. The
electron emitted is called a beta
particle.
• Positron emission- elements below the
band of stability have too many protons. A
proton can be turned into a neutron by
emitting a positron – a particle that has
the same mass as an electron, but has a
positive charge and is emitted from the
nucleus during some types of radioactive
decay.
• Nuclides with too many protons undergo a
type of radioactive decay called electron
capture, an inner orbital electron is
captured by the nucleus of its own atom.
• Gamma rays- high energy emr waves
emitted from a nucleus as it changes from
ground state to excited state.