1. V ALENCE E LECTRONS AND E LECTRON C ONFIGURATIONS 1

2. V ALENCE E LECTRONS Valence electrons are electrons found on the outer energy shell of an atom Electrons available to be lost, gained, or shared in the formation of chemical compounds. Found in the highest energy level. Valence electrons 2

3. V ALENCE E LECTRONS Elements in the same group (family) have the same number of valence electrons 3

4. Q UANTUM A TOM M ODEL 4

5. E LECTRON C ONFIGURATION Energy shells are divided into sub-shells as shown in the research of Erwin Schrödinger and Werner Heisenberg The sub-shells are labeled as the s, p, d, and f sub-shells. The sub-sells each hold a certain number of orbitals Each orbital can hold 2 electrons Electron configuration: A shorthand way to keep track of all the electrons in an atom of an element for all the sub-shells that have electrons. The number of electrons in each sub-shell is shown as a superscript. 5

6. E LECTRON C ONFIGURATION Electron Shells (n= 1, 2, 3, 4…) The letter n represents the main shell or energy level. The maximum numbers of electrons that can occupy the main shells The electron shells in the shell model of an atom (except for n =1) are divided into sub-shells. Energy Level # of electrons per energy level (2n 2 ) 12 28 318 432 6

7. E LECTRON S UB -S HELLS ( S, P, D, AND F ) o Each sub-shell is indicated by its main shell number and a letter, either s, p, d, or f. o The sub-shell in each shell is the same as the shell number. o o The maximum numbers of electrons that can occupy s, p, d, and f sub-shells are 2, 6, 10, and 14, respectively sub- shell # of electrons in sub shell s2 p6 d10 f14 7

8. E LECTRON C ONFIGURATION 8 Sub-shells can be seen by the separation on the periodic table. Helium is part of the s sub-shell.

9. E LECTRON C ONFIGURATION In an electron configuration, the number indicates the shell number the letter indicates the sub-shell within the shell the superscript indicates the number of electrons in the sub-shell. The superscript numbers sum to the total number of electrons for an atom of the element Example: carbon has six electrons and its electron configuration is 1s 2 2s 2 2p 2 2 +2 +2 =6 total electrons 9

10. T HE ORDER TO FOLLOW 10 Remember: S orbitals= 2 e- P orbitals= 6 e- D orbitals = 10 e- F orbitals = 14 e-

11. E LECTRON C ONFIGURATION AND THE PERIODIC TABLE 11

12. P RACTICE Write the following elements electron configurations. Li, Lithium K, Potassium Kr, Krypton Pb, Lead 12

13. P RACTICE Answers Li, Lithium 1s 2 2s 1 K, Potassium 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 Kr, Krypton 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 Pb, Lead 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 2 13

14. N OBLE G AS CONFIGURATION To write a noble gas (shorthand) configuration for any element, count backwards from that element until you reach a noble gas. Write that element in brackets. Then, continue forward with next sub-shell(s) - see the following version of the periodic chart that shows the sub-shell order with respect to the elements. 14

15. N OBLE G AS CONFIGURATION 15

16. N OBLE G AS CONFIGURATION For example, if we wanted to do the shorthand configuration for sodium (Na), you would count back one element to neon (Ne) and put Ne in brackets. [Ne] Put this element symbol in brackets and then, noting that the next correct sub-shell is 3s, include the rest of the electrons as we did with the smaller elements. [Ne]3s 1 16

17. P RACTICE Write the following noble gas configuration for the following elements. Be, Beryllium F, Fluorine Pt, Platinum 17

18. P RACTICE Write the following noble gas configuration for the following elements. Be, Beryllium [He]2s 2 F, Fluorine [He]2s 2 2p 5 Pt, Platinum [Xe]6s 2 4f 14 5d 8 18