Rutherford’s Gold Foil Experiment

2. Most alpha particles went straight through Some of the particles deflected back to the source. Conclusion: Atom made up mostly of empty space. Nucleus has an overall positive charge. Rutherford’s Gold Foil Experiment

3. Bohr’s “Planetary” Atom Model

4. Wave-Mechanical Model

5. Orbit vs. Orbital • An orbit describes a particular path that an object follows as it travels around another object • For example, the moon has an orbit about the earth • Electrons do not follow a particular path around the nucleus • Instead, an orbital describes the areas around the nucleus where an electron is most likely to be found (probability of location) • The exact path of an electron in this area is not known

8. ISOTOPES • Atoms of the same element that have different numbers of neutrons. • There are two methods of identifying isotopes. 1. Write mass number with a hyphen after the name of the element, ex: Helium-3 or Helium-4, and 2. using the composition of the nucleus as the isotopes nuclear symbol, ex. 3He or 4He (the number of the bottom left would represent the atomic number which is the number of protons, and therefore never changes.

9. Atomic Mass • The average of all the naturally occurring isotopes of an element. • MUST know how to calculate it!!!! • Ex: Naturally occurring chlorine is 75.78% 35Cl, which has an atomic mass of 34.969 amu, and 24.22% 37Cl, which has an atomic mass of 36.966 amu. Calculate the average atomic mass (that is, the atomic weight) of chlorine. • hello drmcguiness ;D

10. FIRST PRINCIPLE ENERGY LEVEL: holds only 2 electrons. • SECOND PRINCIPLE ENERGY LEVEL: holds only 8 electrons. • THIRD PRINCIPLE ENERGY LEVEL: holds only 18 electrons. • FOURTH PRINCIPLE ENEGY LEVEL: holds only 32 electrons. Valence Electrons - The number of electrons in the last principle energy level. According to the octet rule, there can be no more than 8 valence electrons. These electrons affect chemical properties of the element. Non-Valence Electrons - All other electrons in an atom other than the last level (valence)

11. Ground vs. Excited States • In this class we will be performing an experiment called the “Flame Test”. We will be heating up metal powders in order to excite the electrons to jump from a lower energy level to a higher energy level. • When an electron returns from a higher energy state to a lower energy state, it emits a specific amount of energy usually in the form of light. This is known as a bright line spectrum, and can be used to identify an element like a fingerprint.

12. Bright Line Spectrum While this light appears as one color to our eyes, it is actually composed of many different wavelengths each of which can be seen using a spectroscope The energy that is given off when an excited electron falls to the ground state is separated into its component wavelengths.

13. Ions An atom with a charge. We can never change the number of protons! So to produce a charge we can add or subtract electrons Atoms lose or gain electrons in order to have a complete outer shell (to become more stable), and follow the octet rule.

14. Lewis Dot Diagrams Helps to show the number of valence electrons in the last principle energy level. There can only be 2 electrons on each side of the symbol of the element. Put the 1st and 2nd valence electrons on any side of X. For the 3rd, 4th, and 5th electrons, put each electron on a different side of the symbol. For the 6th, 7th and 8th electrons, add them to any side with 1 electron.