Models of the Atom

1. Models of the Atom

2. Lets Review! • Orbitals • Ground vs Excited state • Electromagnetic spectrum • Photons and waves • Flame test • Atomic Emission Spectrum • Spectroscope 2

3. l. Models of the Atom • There were many different models over time • Dalton-billiard ball model (1803) • Thompson – plum-pudding model (1897) • Rutherford – Nuclear model of the atom (1911) • Bohr – uses quantized energy of the atom (1913) • Quantum Mechanical Model of the Atom (1926)

4. ll. Problems with the Bohr Model • The model is fundamentally incorrect and only works with hydrogen. • Failed to explain the spectrum of any other element • Did not account for the chemical behavior of atoms • Electrons do not move around the nucleus in circular orbits • Laid ground for later atomic models.

5. lll. Quantum Mechanical Model of the Atom • Quantum Mechanical Model is the current description of electrons in atoms. • It does not describe the electron’s path around the nucleus • Quantum Mechanical Model based on several ideas including: • Schrodinger wave equation (1926) is mathematical equation describing the behavior of an electron and treats electrons as waves. • Heisenberg uncertainty principle (1927) states that it is impossible to know both the velocity and position of a particle at the same time.

6. lV. Atomic Orbital • Using the quantum mechanical model you can predict the electron’s location in an atom • An atomic orbital is a region of space in which there is a high probability of finding an electron • Orbitals are not necessarily spherical How are these different from the orbitals found in Bohr’s model?

7. Question Time • What is the Schrodinger Equation? • How does it treat electrons? • What is the Heisenberg Uncertainty Principle? • What is an atomic orbital?

8. V. Quantum Numbers • The Quantum Mechanical Model assigns quantum numbers to indicate the relative sizes and energies of atomic orbitals. • There are three things for every electron • Principal energy level (principal quantum number, n) • Energy Sublevel (s, p, d, f) • Atomic orbital

9. Vl. Principal Energy Levels What tool do you think we use to find the energy levels of the electrons? • Principal energy levelsn =1 to 7. (Row # on the periodic table) • The electron’s principal energy level is based on its location around the nucleus. • Electrons closer to the nucleus are at a lower energy level and have lower energy than those farther away from the nucleus How is this similar to Bohr’s model? Different?

10. Question Time • What do quantum numbers indicate? • What is the principal energy level based on? • Describe the energy as you go further from the nucleus

11. Vll. Energy Sublevels and Orbitals • Energy sublevels • assigned letters s, p, d or f (smart people do fine) • Energy sublevels correspond to a shape where the electron is likely to be found. • Orbitals – describes the electron’s location • 2 electrons per orbital • s sublevel has 1 orbital (2 electrons total) • p sublevel has 3 orbital (6 electrons total) • d sublevel has 5 orbital (10 electrons total ) • f sublevel has 7 orbital (14 electrons total) Looking at the periodic table can you see any connections to the orbitals and sublevels ?

13. s orbital (1) - spherical

14. p orbitals (3) – dumb-bell shaped

15. d orbitals (5)

16. f-orbitals (7)

17. Question Time • What letters are assigned to the energy sublevels? • How many orbital(s) does the s sublevel have? p sublevel? d sublevel? f sublevel? • How many electrons can one orbital hold?