1. Title: Lesson 5 Drawing Electron Configurations Learning Objectives: Know how to write full electron configurations using ideas of subshells Understand how to use Aufbau, Pauli and Hund principles to write and draw electron configurations

2. STARTER How many electrons? Can be held in an s orbital? Can be held in a p orbital? Can be held in a d orbital? Can be held in an f orbital?

3. SHELLS, SUB-SHELLS AND ENERGY LEVELS 1 2 3 4 INCREASING ENERGY / DISTANCE FROM NUCLEUS A study of First Ionisation Energies across each period suggested that each ‘shell’ was in fact a group of ‘sub-shells’ at different but similar energy levels. The electrons in different sub-shells have different energy levels. Shell 1 contains only an s sub-shell Shell 2 contains an s and p sub-shell Shell 3 contains an s, p and d sub-shell Shell 4 contains an s, p, d and f sub-shell SUB SHELLS PRINCIPAL QUANTUM NUMBER OF SHELL How are electrons arranged within these sub-shells? s p d f s s p s p d

4. Orbitals are filled from the lowest energy level upwards. (The Aufbau Principle) The quantum shells get closer together in space as you get further from the nucleus. There is an overlap in the energy levels of the sub-shells of different shells. The first example occurs when the 4s orbital is filled before the 3d orbitals because it is at a lower energy level. The 4s orbital is still part of the forth shell and is physically further from the nucleus than the 3d sub- shell. INCREASING ENERGY / DISTANCE FROM NUCLEUS 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f PRINCIPAL QUANTUM NUMBER OF SHELL SUB SHELLS 1 1s 2 2s 2p 3d 3 3s 3p 4s 4 4p 4d 4f PRINCIPAL QUANTUM NUMBER OF SHELL SUB SHELLS ORDER OF FILLING ORBITALS

5. The following sequence will show the ‘building up’ of the electronic structures of the first 36 elements in the periodic table. Electrons are shown as half headed arrows and can spin in one of two directions s orbitals p orbitals d orbitals 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS

6. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS HYDROGEN 1s 1 THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS Hydrogen atoms have one electron. This goes into a vacant orbital in the lowest available energy level. The Aufbau Principle FILL LOWEST ENERGY LEVEL FIRST. (GIVES LOWEST (POTENTIAL) ENERGY)

7. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS HELIUM 1s 2 THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS Every orbital can contain 2 electrons, provided the electrons have opposite ‘spins’. The two electrons in a helium atom can both go in the 1s orbital. Pauli’s Exclusion Principle MAX NUMBER IN EACH ORBITAL = 2. MUST HAVE OPPOSITE SPIN!

8. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS LITHIUM Orbitals hold a maximum of two electrons, so the third electron in a lithium atom must go into the next available orbital. This is the 2s orbital. An s orbital is lower in energy than a p orbital in the same shell. 1s 2 2s 1

9. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS BERYLLIUM Beryllium atoms have four electrons, so the fourth electron pairs up in the 2s orbital. The 2s sub-shell, which only contains the 2s orbital, is now full. 1s 2 2s 2

10. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS BORON As the 2s sub-shell is now full, the fifth electron goes into one of the three p orbitals in the 2p sub-shell. The 2p orbitals are slightly higher in energy than the 2s orbital but each are at the same energy level, they are ‘degenerate’. 1s 2 2s 2 2p 1

11. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f HUND’S RULE OF MAXIMUM MULTIPLICITY INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS CARBON The next electron doesn’t pair up with the other 2p electron as there is an empty orbital available of the same energy. There is less repulsion between the electrons when in separate orbitals resulting in an arrangement of lower energy and more stability. 1s 2 2s 2 2p 2 MAX NUMBER OF ELECTRONS WITH SAME SPIN!

12. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS NITROGEN The next electron goes into the vacant p orbital of the same energy. All three electrons are now unpaired. Less repulsion Lower energy More stability. 1s 2 2s 2 2p 3 HUND’S RULE OF MAXIMUM MULTIPLICITY

13. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS OXYGEN With all three orbitals half-filled, the eighth electron in an oxygen atom must now pair up with one of the 2p electrons. The repulsion between the two paired electrons raises their energy level. This explains the drop in first ionisation energy from N to O. 1s 2 2s 2 2p 4

14. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS OXYGEN With all three orbitals half-filled, the eighth electron in an oxygen atom must now pair up with one of the 2p electrons. The repulsion between the two paired electrons raises their energy level. This explains the drop in first ionisation energy from N to O. 1s 2 2s 2 2p 4

15. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS SODIUM - ARGON Na 1s 2 2s 2 2p 6 3s 1 Mg 1s 2 2s 2 2p 6 3s 2 Al 1s 2 2s 2 2p 6 3s 2 3p 1 Si 1s 2 2s 2 2p 6 3s 2 3p 2 P 1s 2 2s 2 2p 6 3s 2 3p 3 S 1s 2 2s 2 2p 6 3s 2 3p 4 Cl 1s 2 2s 2 2p 6 3s 2 3p 5 Ar 1s 2 2s 2 2p 6 3s 2 3p 6 Remember, Hund’s Rule is followed. Electrons remain unpaired if a vacant p orbital is available. This provides a lower energy level as the electrons repel less than when paired.

16. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS POTASSIUM The 4s orbital is of a LOWER ENERGY than that of the 3d orbitals. The 4s gets filled first! 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 The Aufbau Principle

17. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS SCANDIUM There are five d orbitals. They are ‘degenerate’ i.e. are at the same energy level. So they are each filled with a single electron before any is filled with two ‘spin paired’ electrons. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 WATCH OUT FOR TWO SPECIAL CASES ! HUND’S RULE OF MAXIMUM MULTIPLICITY

18. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS TITANIUM 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2 These are the transition metals also known as the d block elements. The highest energy electron enters a d orbital HUND’S RULE OF MAXIMUM MULTIPLICITY

19. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS VANADIUM 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3 The 3d orbitals are part of the 3 rd shell, which is an inner shell closer to the nucleus than the 4s orbital of the 4 th shell. Therefore, the atomic size of d block elements remains relatively constant across a period. Nuclear charge is increased by one proton but is shielded by one inner shell 3d electron. So, the 4s electrons experience an approximately unchanged nuclear attraction across the d block.

20. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS CHROMIUM One would expect the electronic configuration of the chromium atom to be [Ar] 4s 2 3d 4. The 4s and 3d orbitals are close in energy. The arrangement of six unpaired electrons has a lower energy than if two electrons are paired (repelling each other) in the 4s orbital. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5

21. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS MANGANESE The new electron goes into the 4s orbital to restore its filled state. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5

22. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS IRON 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6

23. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS COBALT 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7

24. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS NICKEL 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8

25. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS COPPER One would expect the configuration of chromium atoms to be… [Ar] 4s 2 3d 9. However, the actual arrangement… [Ar] 4s 1 3d 9 Is of lower energy and therefore the stable arrangement. This can be rationalised by the symmetry of the full 3d sub-shell. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10

26. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS ZINC The electron goes into the 4s orbital to restore its filled state. The inner 3 rd shell is now complete. Zn is the last d block element in the 4th period. The available orbitals of next highest energy are the 4p and and these fill next. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10

27. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS GALLIUM - KRYPTON The 4p orbitals are filled in exactly the same way as the 3p orbitals were. These elements are in the p block. The highest energy electron is in a p orbital.

28. 1 1s 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS THE ELECTRONIC CONFIGURATIONS OF THE FIRST 36 ELEMENTS GALLIUM - KRYPTON Ga 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 1 Ge 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 1 Or, in shortened form… As[Ar]4s 2 3d 10 4p 3 Se [Ar]4s 2 3d 10 4p 4 Br [Ar]4s 2 3d 10 4p 5 Kr [Ar]4s 2 3d 10 4p 6

29. Creating spin diagrams

30. 1s 2 2s 2 3s 2 4s 2 5s 2 6s 2 7s 2 2p 6 3p 6 4p 6 5p 6 6p 6 3d 10 4d 10 5d 10 6d 10 4f 14 5f 14 1 2 3 4 5 6 7 So, the pattern for reading the electron configurations right off the periodic table is this: If you are wanting to write the electron configuration for any element, just follow this pattern and remember to stop at the element you’re representing.

31. The relative energy of the orbitals depends on the atomic number Energy of an orbital depends on attractions between the electrons and the nucleus and inter-electron repulsions. All the sub levels in the third energy level (3s, 3p and 3d), for example, have the same energy level for the hydrogen atom and only become separated as extra protons and electrons are added. 4s and 3d complications… 3d and 4s levels are very close in energy and are very sensitive to inter- electron repulsion. For Potassium and Calcium, 4s is filled before the 3d sub level. Once the 3d subshell is filled, and then the 4s subshell is filled, 3d will fall below 4s (after Calcium).

32. Orbital Diagrams/Drawing Electron Configuration Diagrams Different ways of drawing the orbital/electron configuration diagrams: These are better to show the increase in energy levels!

33. Complete the Test Yourself Questions Page 71 Question 12 a-c Check your answers on page 560

34. Questions 1.Which orbital would the electrons fill first? The 2s or 2p orbital? 2.Can you have an electron in between two orbitals? 3.How many d orbitals are there in the d subshell? 4.How many electrons can the p orbitals hold? 5.Why can two electrons occupy the same orbital? 1.The 2s orbital would be filled before the 2p orbital because orbitals that are lower in energy are filled first and the 2s orbital is lower in energy than the 2p orbital. 2.You cannot have an electron in between two orbitals. The electron will either be in one orbital or the next. 3.There are 5 d orbitals in the d subshell. 4.A p orbitals can hold 6 electrons. 5.Two electrons can occupy the same orbital because they each have a different spin. There cannot be two electrons that have the same exact orbital configuration and spin. 1.The 2s orbital would be filled before the 2p orbital because orbitals that are lower in energy are filled first and the 2s orbital is lower in energy than the 2p orbital. 2.You cannot have an electron in between two orbitals. The electron will either be in one orbital or the next. 3.There are 5 d orbitals in the d subshell. 4.A p orbitals can hold 6 electrons. 5.Two electrons can occupy the same orbital because they each have a different spin. There cannot be two electrons that have the same exact orbital configuration and spin.

35. THE AFBAU (BUILDING UP) PRINCIPLE “Electrons enter the lowest available energy level.” HUND’S RULE OF MAXIMUM MULTIPLICITY “When in orbitals of equal energy, electrons will try to remain unpaired.” STARTER Create an energy level diagram of potassium. MAIN ACTIVITY 2 2s 2p 4s 3 3s 3p 3d 4 4p 4d INCREASING ENERGY / DISTANCE FROM NUCLEUS

37. Remember exceptions to the rules… Copper and Chromium are the exceptions… 4s and 3d orbitals are close in energy, the electron configuration for chromium with a half full d sub level minimizes electrostatic repulsion with six singly occupied orbitals. Half filled and fully filled sub shells are stable… Cr: Half filled d sub shellCu: Fully filled d sub shell

38. Valence Electrons These are electrons in the outer energy level are responsible for compound formations. Examples: Lithium has one valence electron in the outer second energy level (2s 1 ) Beryllium has two (2s 2 ) Boron has three (2 s 2p 1 )

40. Solutions 19. 20. 21.

41. Solutions 22. 23. 24.