Electrons in Atoms Quantum Mechanical Model

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 ( ) 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.

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.

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.

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)

Table 12.1: Energy levels, Sublevels, and Orbitals Principle Energy LevelNumber of sublevelsType of sublevel N = 111s (2 electrons) N = 222s, 2p, (8 electrons) N = 333s, 3p, 3d (18 electrons) N = 444s, 4p, 4d, 4f (32 electrons) () = maximum number of electrons in that principal energy level.

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.

Electron Configurations = The ways in which electrons are arranged around the nuclei of atoms. 1.Aufbau principle = electrons enter orbitals of lowest energy first. 2.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) 3.Hund’s Rule = electrons enter orbitals of the same energy level 1 orbital at a time before filling in the second.

Pg. 328; 5 a-f

Pg. 332; 8-9

Unit Assignment Part 1 Pg. 346; 24, (due 3/14)