2. Electron Basics

3. Atom Review  Protons and neutrons are bound together to make the atomic nucleus  Protons have a positive electrical charge  Neutrons are neutral and have no electrical charge

4. What is an electron?  It is a sub-atomic particle that can be found around the atomic nucleus.  It has a negative electric charge  Its mass is about 2000x less than a proton or neutron  It is a sub-atomic particle that can be found around the atomic nucleus.  It has a negative electric charge  Its mass is about 2000x less than a proton or neutron

5. Where is an electron?  Danish physicist Neils Bohr proposed the idea that electrons can be found around the nucleus in different energy levels or shells.  One cannot pinpoint the location of an electron, only about where it is in a specific energy level or shell

6. Electron Shells  There are 7 electron shells (How many periods, or rows are on the periodic table?)  Each shell can hold a specific number of electrons  # of elements in the period = # of electrons that shell can hold  Q: How many electrons can the 2nd electron shell hold?  A: 8  There are 7 electron shells (How many periods, or rows are on the periodic table?)  Each shell can hold a specific number of electrons  # of elements in the period = # of electrons that shell can hold  Q: How many electrons can the 2nd electron shell hold?  A: 8

7. Electron Shell Capacity - 1st 18 elements  1st Shell: 2 e -  2nd Shell: 8 e -  3rd Shell: 8 e -  Electrons fill each shell from the inside out. Ex: the 1st shell is filled first  1st Shell: 2 e -  2nd Shell: 8 e -  3rd Shell: 8 e -  Electrons fill each shell from the inside out. Ex: the 1st shell is filled first

8. Valence Electrons  Electrons in the outermost shell are called valence electrons.  They are involved in chemical bonding and reactions.  We will talk much more about these electrons when we talk about chemical reactions in later chapters.  Electrons in the outermost shell are called valence electrons.  They are involved in chemical bonding and reactions.  We will talk much more about these electrons when we talk about chemical reactions in later chapters.

9. Bohr Diagrams  A conceptual model of an atom  # of n and # of p are written in the nucleus (center circle)  # of e - are filled in each shell until it is full (How many can each shell hold?)  Once a shell is full, you add another circle and continue.

10. Bohr Diagram Practice  Pick 3 elements from the first 18 elements, and create Bohr Diagrams for those elements.

11. References  The Atom - http://www.danieltrimpey.com/learn/ electronics/images/atom.gif