1. Electrons in Atoms Notes Electrons in Atoms Notes Electron Configurations Quantum model

2. Electron Configurations the arrangement of electrons in an atom the arrangement of electrons in an atom each type of atom has a unique electron configuration each type of atom has a unique electron configuration electrons tend to assume positions that create the lowest possible energy for atom electrons tend to assume positions that create the lowest possible energy for atom ground state electron configuration- lowest energy arrangement of electrons ground state electron configuration- lowest energy arrangement of electrons

3. Rules for Arrangements Aufbau Principle- an electron occupies the lowest-energy orbital that can receive it Aufbau Principle- an electron occupies the lowest-energy orbital that can receive it Beginning in the 3 rd energy level, the energies of the sublevels in different energy levels begin to overlap Beginning in the 3 rd energy level, the energies of the sublevels in different energy levels begin to overlap

4. Rules for Arrangements Pauli Exclusion Principle- no two electrons in the same atom can have the same set of 4 quantum numbers Pauli Exclusion Principle- no two electrons in the same atom can have the same set of 4 quantum numbers Hund’s Rule- orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second Hund’s Rule- orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second all unpaired electrons must have the same spin all unpaired electrons must have the same spin

5. Rules for Arrangements

6. Writing Configurations Orbital Notation: Orbital Notation: an orbital is written as a line an orbital is written as a line each orbital has a name written below it each orbital has a name written below it electrons are drawn as arrows (up and down) electrons are drawn as arrows (up and down) Electron Configuration Notation Electron Configuration Notation number of electrons in sublevel is added as a superscript number of electrons in sublevel is added as a superscript

7. Order for Filling on the Periodic Table

8. S p d f sublevel orbitals - shape is based on the probability of an electron to be somewhere at any given time

9. Writing Configurations Start by finding the number of electrons in the atom Start by finding the number of electrons in the atom Identify the sublevel that the last electron added is in by looking at the location in periodic table Identify the sublevel that the last electron added is in by looking at the location in periodic table Draw out lines for each orbital beginning with 1s and ending with the sublevel identified Draw out lines for each orbital beginning with 1s and ending with the sublevel identified Add arrows individually to the orbitals until all electrons have been drawn Add arrows individually to the orbitals until all electrons have been drawn

10. Silicon number of electrons: 14 number of electrons: 14 last electron is in sublevel: 3p last electron is in sublevel: 3p 1s 2s 2p 3s 3p  Valence Electrons- the electrons in the outermost energy level

11. Chlorine number of electrons: 17 number of electrons: 17 last electron is in sublevel: 3p last electron is in sublevel: 3p 2p 3s 3p 1s 2s

12. Sodium number of electrons: 11 number of electrons: 11 last electron is in sublevel: 3s last electron is in sublevel: 3s 1s 2 2s 2 2p 6 3s 1 1s 2s 2p3s

13. Calcium number of electrons: 20 number of electrons: 20 last electron is in sublevel: 4s last electron is in sublevel: 4s 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 1s 2s 2p3s 3p 4s

14. Bromine number of electrons: 35 number of electrons: 35 last electron is in sublevel: 4p last electron is in sublevel: 4p 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5 1s 2s 2p 3s3p 4s3d 4p 1s 2s 2p 3s3p 4s3d 4p

15. Argon number of electrons: 18 number of electrons: 18 last electron is in sublevel: 3p last electron is in sublevel: 3p 1s 2 2s 2 2p 6 3s 2 3p 6 1s 2s 2p 3s3p

16. Noble Gas Notation short hand for larger atoms short hand for larger atoms configuration for the last noble gas is abbreviated by the noble gas’s symbol in brackets configuration for the last noble gas is abbreviated by the noble gas’s symbol in brackets