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Transcript of atomictheory_web_f12_000.pdf
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Principles of Imaging Science I (RAD119)
Physics Fundamentals &
Atomic Structure
Goals Understand the structure of matter and the
fundamentals of electromagnetic radiation.
Understand the concept of x-ray production, how x-rays interact with matter, the quantity and
quality of the x-ray beam, and demonstration of
anatomic structures in the radiographic image (radiograph)
An Art and a Science
Radiography as art
Scientific method
Natural science
o Physical science: non-living matter
Physics
o Biological science: living matter
Anatomy and Physiology
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Matter and Energy
Physics studies relationships between matter and energy
Matter o Mass and occupies space
Energy is force used to do work
Matter Matter
Anything that occupies space, has shape or form, and has mass
States of matter: Solid, liquid, gas
Mass Amount or quantity of matter in an object.
Does not change with a change in the form
Does not change with gravitational force
Air has mass, but much less than a rock that has the same volume because the particles of matter in air are
more widely spaced.
Fundamental Unit - Atom Composed of smaller units protons,
neutrons, and electrons
Atomic Theory
Basic building blocks of matter
Atom is unique and characteristic of a certain type of matter
oHydrogen atom is different from an atom
of Barium or Calcium
Atoms cannot be seen o Scientists theorized about its structure and function based
on experimentation
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Atomic Structure
Nucleus
Small, dense center
Contains nucleons protons and
neutrons
Electrons
Orbit nucleus
Bohr Atom Basic structure of atoms is comparable to
our solar system
An atom is mostly empty space the space between the electrons and the nucleus is like the space between the earth and sun
Atom is comprised of a small, dense, positive nucleus and negative electrons revolving in orbit around the nucleus
Bohr Atom
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Basic Atomic Particles
Proton
Positive charge
Represents the Atomic Z#
Distinguishes elements by number of protons in the nucleus
Change the Z#, change the element!
Basic Atomic Particles Neutron
Neutral charge
Stability of nucleus
Serve in the role in radioactive atoms (isotopes)
Electron
Negative charge
Electrical stability maintained through equal number of protons and electrons
Atomic Mass Unit (amu) Unit used to measure atomic mass.
It is not a metric unit, based on the standard of the carbon-12 atom.
The equivalent mass in kilograms notes the small size of an atomic mass unit
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Electrons Electrons (-) charge
Subatomic particle
Small quantity of mass
Located outside nucleus in orbital shells
Stable atoms have equal electrons as protons
Electron shells Ordered from the first shell (K) to
the last shell (Q)
Electron Shells Represent the energy levels
Maximum number of electrons in each shell based upon 2n2
K shell: Shell #1 = 2 electrons (innermost)
L shell: Shell #2 = 8 electrons (2)(2)2
M shell: Shell #3 = 18 electrons (2)(3)2
Q shell: Shell # 7 = 98 electrons (2)(7)2
A maximum of 8 electrons may comprise the outermost shell of any atom (valence shell)
Electron Shell Maximum
Factoid: The largest naturally occurring atom, uranium, has a total of 92 electrons in its
seven shells. Even in this atom, shells 5, 6, and 7 are not completely filled.
Shell
Number
Principle
Quantum #
Shell Symbol Number of
Electrons
1 K 2
2 L 8
3 M 18
4 N 32
5 O 50
6 P 72
7 Q 98
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Forces Nuclear Binding Energy
Holds protons and neutrons together in the nucleus
Sum of the strong nuclear forces that attract
and pull the protons and neutrons together in the nucleus
Measure of the amount of energy needed to
split the atom If a particle shot at the atom strikes the nucleus with
the energy equal to the nucleus's binding energy, the atom could break up or "split."
Forces Centripetal force
Maintains electron in orbit preventing it from flying away from the nucleus
Center seeking force Balances the force created by the electron velocity
Forces
Centrifugal force
Maintains electron at a distance from the nucleus while moving around the nucleus
Out from center force
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Forces Electron Binding Energy (BE)
Maintains electrons in their shells
Dependent upon:
Proximity to nucleus
Higher BE closer to nucleus
Total # electrons in the atom
Higher BE in larger atoms
Most of the BE comes from the force of attraction between the electrons and
protons
Electron Binding Energy (Eb)
Energy needed to eject electron from atom
TUNGSTEN
(Eb)Comparison
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Electron Binding Energy
CHARGE & IONS
Neutral atoms: equal # of electrons and
protons
Balanced or stable
If an electron is added or removed the atom is no longer neutral: it becomes electrically charged.
Negative ion - An atom with an extra electron
Positive ion - - An atom that has one fewer electrons than protons
IONS
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IONS
Ionization Adding or removing an electron from its
shell
An atom in which this has occurred is called an ion.
If an electron is added, termed a negative ion (-1 charge)
If an electron is removed, termed a positive ion (+1 charge)
Ionization
Positive or Negative Ion??
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ATOMIC NUMBER & ATOMIC MASS NUMBER
ATOMIC NUMBER ATOMIC MASS NUMBER
Definition: Equal to the number of protons in
the nucleus of an atom
Elements Z number
Definition: Equal to the number of protons and
neutrons in an atom
Elements A number
May be measured using amu (atomic
mass unit)
ATOMIC MASS NUMBER &
ATOMIC NUMBER
Both the A number (atomic mass number)
and Z number (atomic number) are often
given to represent an element Y as follows:
A
Y Z
Periodic Table of Elements Arranged based on increasing atomic #
Groups are vertical columns
Represent same # electrons in outermost shell Similar chemical characteristics
Group I, II: Light metals Groups III VI: Non-metals Group VII: Halogens Group VIII: Noble gases
Periods are horizontal rows
Represent the total number of electron shells
Interpretation of Table
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Periodic Table of Elements
Non-Metals
Periodic Table of Elements http://www.periodicvideos.com/#
Periodic Table of Elements No set ratio of neutrons to protons in atoms
Larger and more stable the atom, the higher its ratio of neutrons to protons.
Many stable atoms with a low atomic number have about the same number of neutrons
and protons.
Heavier elements may have almost twice as many neutrons as protons.
greater strong nuclear force is needed
to help stabilize such atoms to keep the
nucleus from breaking up.
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Nuclear arrangements
Isotope
Atoms with same atomic number Unstable isotopes often have a deficient or excess
number of neutrons. This causes them to spontaneously change from one element to another.
Considered radioactive, referred as radioisotopes
Isobar
Atoms with same atomic mass
Isotone
Atoms with same neutron number
Nuclear Arrangements
Nuclear Arrangements
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Combination of Atoms
Atoms of different elements may combine to form molecules
Ionic Bonding occurs when an electron from one atom
transfers to another atom
Sodium Chloride (NaCl)
Combination of Atoms Covalent Bonding occurs when two atoms share
some of the same electrons which revolve around
both nuclei Water (H2O)
Video