1. THE ATOM Smallest part of an element that has all of the properties of that element.

2. 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 1 st periodic table (modern table arranges elements that react the same chemically)

3. 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

4. Questions for you What do particle accelerators do? AMU is the acronym for

5. 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

6. 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?

7. A neutral atom has the _____number of electrons in orbits as protons in the nucleus

8. K L M N O P Q

9. 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 2n 2  Atoms with filled outer shells are stable  Number of electrons in outer shell determines the chemical reaction

10. Transitional Elements Fourth period Electrons are added to inner shells Chemical properties of transitional elements are dependent on number of electrons in the TWO OUTERMOST SHELLS

11. CENTI F UGAL FORCE F LYING OUT INTO SPACE

12. CENTRI P ETAL FORCE P ULLING INTO THE CENTER

13. 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

14. THEREFORE The larger the atom, the higher the electron binding energy

15. 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

16. 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

17. Radioactivity What determines if a nucleus of an atom is unstable? Too many or too few neutrons

18. 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

19. 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

20. 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

21. 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