1. Chapter 13 Notes
Electrons in an Atom

2. After the discovery of the nucleus consisting of protons and neutrons, experiments were conducted to determine the location of the electrons and models were developed to represent observation.

3. Models of the Atoms The Bohr Atom Danish physicist Neils Bohr.
His research led him to hypothesize that electrons are found at specific distances from the nucleus like planets rotating around the sun.
His model worked for Hydrogen but did not succeed for heavier atoms.

4. The Quantum-Mechanical Model.
Austrian physicist Erwin Schrodinger.
It is a mathematical model known as quantum mechanics but it can be represented visually. Electrons are not found at certain distances from the nucleus but are located in a region in space that is described by a set of 4 quantum numbers. The exact location of the electron can’t be determined.

5. Four Quantum Numbers 1st quantum number: principal energy level (n)
Describes how far away the electron is from the nucleus.
n= 1, 2, 3, 4… where the 1st energy level is closest to the nucleus and at lowest energy. As the number increases, the electron is found further from the nucleus and has more energy

6. 2nd quantum number: sublevels (l)
This describes the shape of the region the electron is in
Each of the principal energy levels is divided into sublevels.
n = 1 has 1 sublevel
n = 2 has 2 sublevels
n = 3 has 3 sublevels
n = 4 has 4 sublevels and so on
These sublevels are identified by numbers or letters. We will use letters.
The letters corresponding to the first four sublevels are s, p, d, f
The 1st energy level has a s sublevel
The 2nd energy level has s & p sublevels
The 3rd energy level has s, p, & d sublevels
The 4th energy level has s, p, d, & f sublevels

7. 3rd quantum number: orbitals or positions (m)
This describes how many different arrangements in space the sublevels can have.
Any s sublevel has 1 orbital
Any p sublevel has 3 orbitals
Any d sublevel has 5 orbitals
Any f sublevel has 7 orbitals

8. 4th quantum number: spin (s)
Any orbital can only have a maximum of 2 electrons, each having opposite spins.
Every s sublevel can only have a maximum of 2 electrons
Every p sublevel can only have a maximum of 6 electrons
Every d sublevel can only have a maximum of 10 electrons
Every f sublevel can only have a maximum of 14 electrons
Order of electron fill-up:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

9. Electron Arrangement in Atoms
Electron Configuration. Start with 1s and follow the order until all the electrons in the atom have a place. (Animation)
Draw electron configurations for the following elements:
H Be O Al
1s1 1s22s2 1s22s22p4 1s22s22p63s23p1
Ca 1s22s22p63s23p64s2
Zr 1s22s22p63s23p64s23d104p65s24d2

10. Orbital Filling.
Draw a box or circle for each orbital. Place arrows in the box or circle to denote electrons. Maximum of 2 electrons per box. The first arrow is pointing up, the second arrow is pointing down to represent opposite spins.
Draw orbital filling diagrams for the atoms below.
H Be O Al Ca

11. Electron Dot Diagram
Using the symbol for the element, place dots around the symbol corresponding to the outer energy level s & p electrons. Will have from one to eight dots in the dot diagram.
H Be O Al Ca

12. Write electron configuration, orbital filling diagrams, and electron dot diagrams.
Cl Sn Tb Kr