RAD 354 Chapt 3 Structure of Matter
• The atom is the smallest part of an element
that has all the properties of the element
– 112 elements have been identified
92 are natural
20 were artificially produced
Interesting dates - info
• 1808 John Dalton classified elements
according to atomic mass values
• Mendeleev first suggested the periodic table
with 8 groupings
– Atomic number (Z#)= NUMBER OF PROTONS
– Atomic MASS # = elemental mass (A) AND
neutrons
Nuclear model of the atom
• 1911 Ernest Rutherford introduced the
nuclear model of the atom
• 1913 Niels Bohr improved on Rutherford’s
• The “mini solar system” model is now know as
the Rutherford – Bohr model of the atom
Molecules
• Atoms of various elements may combine to
forms moledules
– Sodium (Na) + chlorine (CL) = sodium chloride
(NaCL) = table salt
Chemical Compound
• Is a NEW substance that is formed when two
or more atoms of different elements combine
– Covalent bond – sharing electrons in outer orbital
shells
– Ionic bonding – atoms attracted to each other
because of opposite charges
• Smallest particle of an element is an atom
• Smallest particle of a compound is a molecule
Atoms
• Three main parts:
– Electrons
– Protons
– Neutrons
• Mass of an atom is expressed in atomic mass units
(AMU’s) {1/2 mass of a carbon 12 atom} -AMU’s are
always rounded numbers!
Electron “shells” /Orbitrons
• Shells are lettered K,L,M,N – etc from the
nucleus outward (also numbered 1,2,3,4,5
from the nucleus outward).
• Max POTENTIAL number of electrons in any
shell 2n2
• The number of electrons in the outer most
shell tells which GROUP and PERIOD it exists
in the periodic table
Varied #’s of mass# & atomic#
• Isotope = same # of protons but different # of
neutrons
• Isobar = different # of protons and neutrons
BUT same TOTAL number of nucleons
• Isotones = same # of neutrons BUT different #
of protons
• Isomer = same atomic number and same
atomic mass number- BUT exist at different
energy states (varied nuclear arrangements)
Radioactivity
• Can be emission of alpha, beta or gamma
• Radioactive HALF LIFE = time required for a
quantity of radioactivity to be reduced (decay)
to ½ of it’s original value. NOTE: it will have
the same specific energy constant – BUT only
half the number of decays
Particulate vs electromagnetic
• Which of alpha, beta and gamma are
particulate?
• Which is/are electromagnetic?
354 Chapt 4 Electromagnetic Energy
• Photons
– No mass/charge
– Have velocity, frequency, wavelength and
amplitude
– Follow the “duality therory”
– Travel in discrete bundles of energy called
(Quantum”
Velocity is the speed of light
• 3 X 1010 cm/sec OR 3 X 108 m/sec
• Photon is the smallest quantity of any type
e/m radiation
• Photons have BOTH electric (A/C) and
magnetic qualities
• Travel as sine waves
Units of E/M concern
• Amplitude = height of the sine wave
• Frequency (f) = length of successive points in
the sine wave/cm
– As f increases, so does energy (energy is DIRECTLY
PROPORTIONAL to frequency)
• As velocity decreases, so does frequency
• Velocity = frequency X wavelength
– V= F X ƛ
Electromagnetic Spectrum
• 3 ranges: visible light, RF, x-ray
– All travel the speed of light, but may have diff.
frequency and wavelength
– Visible light is I’d by it’s wavelength, RF by it’s
frequency and x-rays by energy
– Radiation may be ionizing or non-ionizing
• Non may be reflected as well as absorbed
• Ionizing cannot be reflected BUT can be
absorbed/partially absorbed and scattered