THE ATOM
Smallest part of an element that has all of the properties of that element.
HISTORY
Greeks and matter
John Dalton’s atom
Dmitri Mendeleev
Earth, wind, water, air and fire
Matter classified by atomic mass
Hook and eye
Elements composed of identical atoms reacted in the same way
Arranged atoms in order of increasing mass.
Designed 1st periodic table
(modern table arranges elements that react the same chemically)
History cont.
Thomson’s atom
Ernest Rutherford
Neils Bohr
Plum pudding
Electrons are negative (plums)
Pudding is positive
Placed the nucleus in the center
Nucleus had a positive charge
Atom is a mini solar system
Questions for you
What do particle accelerators do?
AMU is the acronym for
Smallest part of an element is a
Smallest part of a compound is a
Fundamental parts of the atom are
Atomic mass number for an electron is
What are the two types of nucleons
Which of the fundamental particles is heaviest?
Which has a positive charge?
Which is electrically neutral?
Nucleons are ______times the mass of an electron
Which particle ultimately determines the chemical behavior of an atom?
A neutral atom has the _____number of electrons in orbits as protons in the nucleus
K L M N O P Q
Electron Arrangement
Review of the Periodic Table
The outermost shell is identified by the period and the number of electrons in the outermost shell is identified by the group
Shell number –n- AKA Principle Quantum Number 2n2
Atoms with filled outer shells are stable
Number of electrons in outer shell determines the chemical reaction
Transitional Elements
Fourth period
Electrons are added to outer shells from inner shells
Chemical properties of transitional elements are dependent on number of electrons in the TWO OUTERMOST SHELLS
CENTIFUGAL FORCE
FLYING OUT INTO SPACE
CENTRIPETAL FORCE
PULLING INTO THE CENTER
Electrostatic attraction
Opposites charges attract
Eb
The closer the electron is to the nucleus, the stronger the Eb.
Eb
The greater the number of electrons, the more tightly they are bound
THEREFORE
The larger the atom, the higher the electron binding energy
We can now deduce
More electrons mean higher atomic number because
The number of electrons = the number of protons and atomic number is determined by the number of protons
In Radiography
Tungsten is used to construct the anode and cathode because it has a high atomic number
A high atomic number means more energy is required to ionize the material
Recall that ionization causes eventual breakdown of material
Radioactivity
What determines if a nucleus of an atom is unstable?
Too many or too few neutrons
Radioactivity
Nucleus is unstable
In an attempt to become stable, emits particles and energy
This is called radioactive decay or disintegration
Atoms are called radionuclide
Alpha
Loses 2 units of positive charge
Loses 4 units of mass
Emits gamma rays
High QF
High LET
Beta
Neutrons converts to a proton
Electron type of particle is ejected
Increases the atomic number by one
Emits gamma rays
IONIZATING RADIATION AGAIN!!!!!
Alpha
Emitted only from nuclei of heavy elements (helium)
Travel quickly thru matter
Ionization is quick
Harmless if deposited outside of body
Inside it can completely irradiate soft tissue
Beta
Longer range than Alpha
Originate from the nuclei of radioactive atoms.
See figure 4-18, pg 56
Radioactive half life
Time needed for a radioisotope to disintegrate into a stable atom
Period of time for the radioactivity to be reduced to half its original value
Never reaches zero