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

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)

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

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.

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.

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

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

Electron Shells Period on the Table of Elements Number of Electron Shells for an atom in that period Example: The element Nitrogen is in the 2 nd period so it has two electron shells

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

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