1. The Bohr Model Mr. Matthew Totaro Legacy High School Chemistry

2. Problems with the Nuclear Atomic Model The Nuclear atomic model could not explain why the negatively charged electrons did not ‘spiral’ into the positively charged nucleus. 2

3. The Planetary Model Niels Bohr Niels Bohr proposed solutions to the problems with the nuclear atomic model Bohr assumed the electrons circled the nucleus in fixed orbits much like the planets orbit the sun. 3

4. The Planetary Model 4

5. The Bohr Model of the Atom The nuclear model of the atom does not explain how the atom can gain or lose energy. Neils Bohr developed a model of the atom to explain how the structure of the atom changes when it undergoes energy transitions. Bohr’s major idea was that the energy of the atom was Quantized (or fixed), and that the amount of energy in the atom was related to the electron’s position in the atom. – Quantized means that the atom could only have very specific amounts of energy. 5

6. The Bohr Model of the Atom: Electron Orbits In the Bohr model, electrons travel in orbits called Energy Levels around the nucleus. – More like shells than planet orbits. The farther the electron is from the nucleus the more energy it has. 6

7. The Bohr Model of the Atom: Orbits and Energy Levels, Continued Each orbit has a specific amount of energy. The energy of each orbit is characterized by an integer—the larger the integer, the more energy an electron in that orbit has and the farther it is from the nucleus. – The integer, n, is called a Quantum Number. – 2n 2 Rule gives # of electrons in each orbital level 7

8. Example: – 1 st shell: 2(1 2 ) = 2(1) = 2 electrons – 2 nd shell: 2(2 2 ) = 2(4) = 8 electrons – 3 rd shell: 2(3 2 ) = 2(9) = 18 electrons – 4 th shell: 2(4 2 ) = 2(16) = 32 electrons

9. Valence Valence shell (energy level)– the outermost shell of an atom Valence electrons – the electrons in the outermost shell of an atom –These are the electrons that atoms use to combine with each other

10. Atoms want full valence shells Cl H I’m lonely

11. Atoms want full valence shells 1 P 0 N H 17P 18 N Cl

12. Hydrogen 1 P 0 N H

13. Helium 2 P 2 N He

14. Lithium 3 P 4 N Li

15. Beryllium 4 P 5 N Be

16. Boron 5 P 6 N B

17. Carbon 6 P 6 N C

18. Nitrogen 7 P 7 N N

19. Oxygen 8 P 8 N O

20. Fluorine 9 P 10 N F

21. Neon 10 P 10 N Ne

22. Sodium 11 P 12 N Na

23. Magnesium 12 P 12 N Mg

24. Aluminum 13 P 14 N Al

25. Silicon 14 P 14 N Si

26. Phosphorus 15 P 16 N P

27. Sulphur 16 P 16 N S

28. Chlorine 17 P 18 N Cl

29. Argon 18 P 22 N Ar

30. Potassium 19 P 20 N K

31. Calcium 20 P 20 N Ca