Atomic Structure

1. Atomic Structure ELECTRON CONFIGURATIONS

3. Thomson model In the nineteenth century, Thomson described the atom as a ball of positive charge containing a number of electrons. Rutherford model In the early twentieth century, Rutherford showed that most of an atom's mass is concentrated in a small, positively charged region called the nucleus. Bohr model After Rutherford's discovery, Bohr proposed that electrons travel in definite orbits around the nucleus. Quantum mechanical model Modern atomic theory described the electronic structure of the atom as the probability of finding electrons within certain regions of space. Development of Atomic Models

4. At high temperatures or voltages, elements in the gaseous state emit light of different colors. • When the light is passed through a prism or diffraction grating a line spectrum results.

5. X-rays are part of the electromagnetic spectrum visible light is part of the electromagnetic spectrum Infrared light is part of the electromagnetic spectrum The Electromagnetic Spectrum 10.2

6. Each element has its own unique set of spectral emission lines that distinguish it from other elements. These colored lines indicate that light is being emitted only at certain wavelengths. Line spectrum of hydrogen. Each line corresponds to the wavelength of the energy emitted when the electron of a hydrogen atom, which has absorbed energy falls back to a lower principal energy level. 10.3

7. Modern View • The atom is mostly empty space • Two regions • Nucleus • protons and neutrons • Electron cloud • region where you might find an electron

8. Instead of being located in orbits, the electrons are located in orbitals. • An orbital is a region around the nucleus where there is a high probability of finding an electron.

9. Quantum Numbers • Four Quantum Numbers: • Specify the “address” of each electron in an atom Principal Quantum Number( n) Angular Momentum Quantum #( l) Magnetic Quantum Number( ml) Spin Quantum Number( ms)

10. Quantum Numbers 1. Principal Quantum Number( n) • Indicates the number of the energy level • As n increase, size of electron cloud increases. • Energy increases as n increases. • 2n2 = maximum # of electrons possible in the energy level • Ex. if n=1, energy level 1, can only have 2 electrons 1s 2s 3s Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

11. s p d f Quantum Numbers 2. Angular Momentum Quantum #( l) • Describes the sublevel within each energy level • # of sublevels = value of principal quantum number of that level • Ex. n=1, has 1 sublevel n=2, has 2 sublevels Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

12. s p d f Quantum Numbers 2. Angular Momentum Quantum #( l) • The lowest sublevel has been named s. • The second sublevel has been named p • The third sublevel has been named d • The fourth sublevel has been namde f Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

13. s Quantum Numbers 2. Angular Momentum Quantum #( l ) • There is just one s sublevel , thus it has one orbital that can hold only 2 electrons. • Orbital: space occupied by one pair of electrons. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

14. Quantum Numbers y y y z z z x x x • 2. Angular Momentum Quantum #( l ) • There are three p sublevels and thus it has three orbitals that can hold only 2 electrons.

15. Quantum Numbers 2. Angular Momentum Quantum #( l ) • There are five d sublevels and thus it has five orbitals that can hold only 2 electrons. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

16. Quantum Numbers 2. Angular Momentum Quantum #( l ) • There are seven f sublevels and thus it has seven orbitals that can hold only 14 electrons. • Too complicated to show with drawings. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

17. Principal Energy Levels 1 and 2 For n=1, it can hold a maximum of 2n2 number of electrons: 2 electrons For n=2, it can hold a maximum of 2n2 number of electrons: 8 electrons

18. Classwork • P 118 # 6 and p122 # 7,8

19. Quantum Numbers 3. Magnetic Quantum Number( ml) • Specifies the exact orbital within each sublevel Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

20. Quantum Numbers 4. Spin Quantum Number( ms) • An orbital can hold 2 electrons that spin in opposite directions. • Indicated by arrows: The arrows indicate 2 electrons spinning in opposite direction Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

21. General Rules For Writing Electron Configurations 1. Pauli Exclusion Principle • Each orbital can hold TWO electrons with opposite spins. • In the following diagrams boxes represent orbitals. • Electrons are indicated by arrows: ↑ or ↓. C. Johannesson

22. 2. Aufbau Principle • Electrons fill the lowest energy orbitals first. • The number represents n, the principal quantum number C. Johannesson

23. 3. Hund’s Rule • Within a sublevel, place one e- per orbital before pairing them. WRONG RIGHT C. Johannesson

24. 2s 2p 1s Notation • Orbital Diagram O 8e- • Electron Configuration 1s2 2s22p4 C. Johannesson

25. He Helium has two electrons. Both helium electrons occupy the 1s orbital with opposite spins. WRITING ELECTRON CONFIGURATIONS ↑ H 1s1 Superscript indicates number of electrons in orbital 1s Hydrogen has 1 electron. It will occupy the orbital of lowest energy which is the 1s. ↑ ↓ 1s2 1s

26. ↑ ↓ ↑ ↓ Be 1s 2s The 2s orbital fills upon the addition of beryllium’s third and fourth electrons. Filling the 2s Sublevel ↑ Li 1s22s1 1s 2s The 1s orbital is filled. Lithium’s third electron will enter the 2s orbital. ↑ ↓ 1s22s2

27. ↑ ↓ ↑ ↓ N 1s 2s 2p The third p electron of nitrogen enters a different p orbital than its first two p electrons to give nitrogen the lowest possible energy. ↑ ↓ ↑ Filling the 2p Sublevel ↑ ↓ B 1s22s22p1 1s 2s 2p Boron has the first p electron. The three 2p orbitals have the same energy. It does not matter which orbital fills first. ↑ ↑ ↑ 1s22s22p3

28. V 1s 2s 2p 3s 4s 3p 3d 1s22s22p63s23p64s23d3

29. Classwork p 128 #14

30. Electron Dot Diagrams • The electrons in the outer energy level (called valence electrons) are the most important electrons for chemical reactions. • Lewis electron dot diagrams are used to represent these outer electrons around the symbol of an element.

31. Examples Select electrons that are in the outer energy level (the ones with the largest principal quantum number): 1s22s1 • Lithium Electron configuration: 1s22s1 Largest principal quantum number is 2 and there is 1 electron in this level Li Valence electron 1. Symbol of element represents nucleus and all electrons except those in outer level 2. Write the electron configuration of element to determine valence electrons. 3. Each side of symbol represents an orbital, draw dots to represent electrons in that orbital.

32. Oxygen: 1s2 2s2 2p4 Oxygen: 1s22s2 2p4 Oxygen: has 6 valence electrons (2 +4) O

33. Krypton: 1s22s2 2p6 3s23p64s23d104p6 Krypton: 1s22s2 2p6 3s23p6 4s2 3d10 4p6 krypton: has 8 valence electrons (2 +6) Kr Classwork p 130 # 15 (Z= atomic number)