Electrons in Atoms

1. Electrons in Atoms Quantum Mechanical Model

2. Atomic Models • John Dalton thought atoms were indivisible….turns out that they are divisible as evidenced by subatomic particles. • Subatomic particles disprove a rigid atom • Joseph John Thomson (1856-1940) gets credit for the discovery of the electron. • “plum pudding atom” • Didn’t account for protons and neutrons and other atomic properties • Ernest Rutherford gets credit for the discovery of the nucleus. • Didn’t account for protons and neutrons in the nucleus • Niels Bohr – electrons are arranged in circular paths, or orbits, around the nucleus. • Does not account for unequal spacing of energy levels in an atom.

3. Quantum Mechanical Model • Atom has no definite shape and electrons do not have precise orbits. • Energy level – region around the nucleus where the electron is most likely to be moving. • Quantum – amount of energy required to move an electron from its present energy level to the next higher level. • The higher the energy level of an electron, the easier it is for the electron to escape from the atom.

4. Quantum Mechanical Model • Erwin Schrödinger (1887 – 1961) wrote and solved a mathematical equation describing the location and energy of an electron in a hydrogen atom. • Lead to the quantum mechanical model. • Mathematical model, not a visible model.

5. Atomic Orbitals • The quantum mechanical model designates energy levels of electrons = principal quantum numbers. • Each principal quantum number refers to a major or principal energy level • n = 1, 2, 3, 4 (distance from the nucleus of the electron increases with increasing n value) • Within each n level there are energy sublevels • Table 12.1 (pg.327)

6. Table 12.1: Energy levels, Sublevels, and Orbitals () = maximum number of electrons in that principal energy level.

7. Atomic Orbitals Defined • = cloud shapes denoted by letters in the quantum mechanical model. (fig. 12.2, pg.327) • S = spherical • P = dumbbell shaped, nodes. • d and f orbitals are complex.

8. Electron Configurations • = The ways in which electrons are arranged around the nuclei of atoms. • Aufbau principle = electrons enter orbitals of lowest energy first. • Pauli exclusion principle = an atomic orbital may describe at most 2 electrons. (keep in mind the number orbitals at each energy level, i.e. 2p has 3 orbitals) • Hund’s Rule = electrons enter orbitals of the same energy level 1 orbital at a time before filling in the second.

9. Pg. 328; 5 a-f

10. Pg. 332; 8-9

11. Unit Assignment Part 1 • Pg. 346; 24, 26-35 (due 3/14)