Electron Configuration Notes

1. Electron Configuration Notes

2. Why are electrons important? • Electrons determine how an atom behaves, what it will or won’t bond/react with. Neutral Atoms • Electrons = negative Protons = positive • This means that neutral atoms have equal numbers of protons and electrons • So, the atomic number tells you the # of electrons too! • Ex: How many electrons does a neutral atom of iron have?

3. Back to Bohr • Although we now believe that electrons orbit the nucleus in a “cloud”, Bohr’s idea of layers (shells, energy levels) is still useful in chemistry. • Visualizing the atom • Predicting interactions with other elements • Visualizing bonds between atoms

4. Electron Configuration • Visualize each layer split into different sub-layers, called subshells or orbitals • They are named the s, p, d, and f orbitals. • Different layers contain certain orbitals, and each orbital can hold a certain number of electrons before it is “full”. • s orbital = 2 electrons • p orbital = 6 electrons • d orbital = 10 electrons • f orbital = 14 electrons

5. Electron Configuration • Sometimes, the orbitals in different layers overlap • This causes the orbitals to fill up in a certain order: • Electrons always fill up orbitals of lower energy first

6. Why is the Periodic Table Set Up So Weird?

7. Electron Configuration • Another way to represent the element • Write the layer and orbital, then the number of electrons that occupy each. • Ex) Hydrogen (atomic # 1) • H: 1s1 • Ex) Nitrogen (atomic # 7) • N: 1s22s22p3

8. Electron Configuration • Sodium (atomic # 11) • Na: 1s22s22p63s1 • Calcium (atomic # 20) • Ca: 1s22s22p63s23p64s2 • Bromine (atomic # 35) • Br: 1s22s22p63s23p64s23d104p5

9. Bohr Diagram • Shows the electrons on each energy level (total number of electrons). • Ex) Boron

10. Bohr Diagram • Start with the nucleus • Then, start filling up the layers with electrons (according to the electron configuration) • Ex) Beryllium • Be: 1s22s2 Be

11. Bohr Diagram • Ex) Chlorine • Cl: 1s22s22p63s23p5 Cl

12. Valence Electrons • In Bohr’s atomic model, each element has a specific number of valence electrons. • Valence electrons are the electrons that reside on the outer shell of the atom. • Valence electrons are important in determining how atoms of different elements react or don’t react with one another (chemical bonding)

13. Valence Electrons • A trick to determining the number of valence electrons: • Look at the group number • Group 1 = 1 valence electron • Group 2 = 2 valence electrons • Group 13 = 3 valence electrons • Group 18 = 8 valence electrons

14. Octet Rule • Octet Rule – An atom’s outer shell is full when it has 8 valence electrons; Noble gasses have this, others try to be like noble gasses • Exception: • Helium is full after only 2 (only has “s” subshell) • Note: pd 4, 5, & 6 must fill up previous “d” shell • To simplify, we’re only going to work with the first 18 elements, periods 1, 2, & 3 (“s” and “p” orbitals)

15. Electron Dot Diagram • An electron dot diagram shows the number of valence electrons. • Usefull in predicting and visualizing chemical bonds • If an atom has 8 electrons surrounding it in the dot diagram, it is a noble gas.

16. Electron Dot Diagram • Write the symbol of the element • Determine the number of valence electrons • Draw the first two on the right hand side of the symbol (this represents the “s” orbital) • Draw the remaining dots one at a time in counter clockwise fashion until you finish • Note, each of the four sides has room for a pair • Ex) Fluorine F

17. Electron Dot Diagram • Ex) Nitrogen N

18. Electron Dot Diagram • Ex) Beryllium Be

19. Putting it all together: • Aluminum • Electron Configuration • 1s22s22p63s23p1 • Bohr Diagram • Electron Dot Diagram Al Al