STRUCTURE OF THE ATOM REVIEW

2. STRUCTURE OF THE ATOM REVIEW NUCLEUS CONTAINS PROTONS AND NEUTRONS ATOMIC NUMBER (Z) = # of PROTONS MASS NUMBER (A) = PROTONS + NEUTRONS ISOTOPES ARE SAME ELEMENT WITH DIFFERENT 
NUMBER OF NEUTRONS

3. ISOTOPE SYMBOL and ISOTOPE NAME Element Name Mass Number Atomic Number Element Symbol Lithium - 6

4. Chemical Reactions Atoms are rearranged to form new substances while 
keeping the chemical identity of the individual atoms. 
Only outer electrons are involved and the release of 
energy is small. VS. Nuclear Reactions Isotopes of one element are converted to isotopes of 
another element, and hence the chemical identity of 
individual atoms changes. The nucleus is involved 
rather than outer electrons and the release of energy is 
large and defined by E = mc2

5. RADIOACTIVITY the spontaneous breaking apart of unstable nuclei in which small particles of matter and/or electromagnetic radiation are emitted Henri Becquerel Credited with discovering radioactivity A)Studied uranium compounds and their ability to fluoresce 
or give off visible light after being exposed to sunlight B)Discovered that uranium gives off invisible rays at all times C)The rays penetrate the light proof cover of photographic 
film and expose it

6. Marie and Pierre Curie Credited with discovery of Ra and Po A) Studied uranium and its ores B) Discovered uranium and uranium 
compounds are only mildly radioactive C) Pitchblende (a uranium ore) has four 
times the amount of radioactivity expected 
based on its uranium content due to other 
isotopes (Ra and Po) present as a result of U 
natural radioactive decay D) Radium is more than a million times as 
radioactive as uranium and polonium is more 
than 5000 times as radioactive as radium

7. Properties of Radioactive Nuclides: 1) They affect the light-sensitive emulsion on a photographic film  2) Produce an electric charge in the surrounding air  3) They produce fluorescence / phosphorescence with certain   compounds  4) Their radiations have physiological effects minimized by time, 
 distance, and shielding 5) They undergo radioactive decay (emit nuclear or ionizing 
 radiation)

8. Nuclear Radiation the particles and energy produced when a nucleus 
undergoes radioactive decay 1)Natural radioactive decay: an unstable element decays to form a 
more stable nucleus 2)Artificial: man-made transmutations done in linear accelerator or 
nuclear reactors

9. Transmutation changing the nucleus of one isotope into a different 
isotope or element

10. Nuclear Stability Affected by the ratio of neutrons to protons Isotopes with an atomic number 1-20 have a neutron to proton ratio of 1:1 Isotopes with an atomic number between 20-83 have a neutron to proton ratio of 1:5 All nuclei above atomic number 83 are unstable and are always radioactive

11. Nuclear Decay Types Beta Decay A high-energy, fast-moving electron is ejected from the nucleus, 
effectively changing a neutron into a proton Charge: Mass Number: Identity Change:

12. Electron Capture A 1s electron is captured by the nucleus, effectively changing a proton to a neutron Charge: Mass Number: Identity Change:

13. Alpha Decay A high-energy, fast-moving +2 charged helium ion is ejected from the 
nucleus 1) Pose the greatest health risk Charge: Mass Number: Identity Change:

14. Gamma-ray Emission Gamma radiation accompanies other types of radioactive decay Charge: Mass Number: Identity Change:

15. Neutron Decay or Capture Neutrons can be emitted or captured by isotopes to increase their stability 1) they pose the next greatest health hazard after alpha particles Example of Neutron Emission Example of Neutron Capture Charge: Mass Number: Identity Change:

16. Decay Properties