1. Chemistry: Inside the Atom Part 3: The Electron E-

2. Electron Arrangement Remember in a neutral atom there are the same number of electrons as protons!!! – Electrons: Travel around the nucleus in paths called orbits (they are negatively charged) – All the electron paths put together make and electron shell (electron cloud)

3. Electron Arrangement Bohr Model 1 P 0 N Nucleus Electron Electron Shell

4. Bohr Model This model focuses on the electrons: – Electrons move in paths around the nucleus of the atom called Energy Levels. – Electrons are found ON energy levels – The farther the energy level from the nucleus, the greater the energy of the electrons there.

5. Bohr Model Continued… Atoms can give off or absorb energy – Electrons can move from 1 energy Level to another – Adding energy (absorbing) = Electrons moving farther from the nucleus – Giving off energy = Electrons moving closer to the nucleus.

6. Bohr Model Nucleus Adding Energy- Electrons moving farther from the nucleus ELECTRON

7. Bohr Model Nucleus Giving Off Energy- Electrons moving closer to the nucleus ELECTRON

8. Electron Shells Period on the Table of Elements Number of Electron Shells for an atom in that period 11 22 33 44 55 66 77 Example: The element Nitrogen is in the 2 nd period so it has two electron shells

9. Electron Shells These shells are represented with a letter – K through Q Look at diagram on the board – Each Electron shell can hold only a certain number of electrons: Electron ShellHow many electrons it can hold K2 L8 M18 N32

10. Inner and Outer Shells A “ K ” shell is complete when it has 2 Electrons. A “ L ” shell is complete when it has 8 electrons. “ M ” and “ N ” shells can hold 18 and 32 electrons when they are inner shells. When an “ M ” or “ N ” shell is an outer shell it can hold only 8 electrons. An outer shell can never hold more than 8 electrons. The electrons in the outer shell are called Valence Electrons