Unit 3 Modern Atomic Theory

Chpt 11 Modern Atomic Theory

Wave Mechanical Model

• Bohr’s atomic model only worked for 1 ELECTRON

• 1920s – quantum mechanics, or wave mechanical model develops

• Louis de Broglie proposed that electrons act as both waves and particles

• See demonstration

Electron probability

• Erwin Schrodinger proposes electron probability through wave function equations

• Where are you most likely to find e-?• Instead of orbits, electrons reside in orbitals, or 3D spaces

around the nucleus • Electron cloud around nucleus with fuzzy edges, no solid

boundary

Uncertainty Principle

• Werner Heisenberg• Uncertainty principle: the position and

momentum of an electron cannot be found at the same time

• Momentum – lose position• Position – shine light on it and excite e-

Principle energy level

• Principle energy level (n) – designates how close an e- is to nucleus, represented as number (1, 2, 3, …)

• Energy closest to nucleus is low and gradually gets higher

• e- are attracted to nucleus and require energy to remove that attraction

• Aufbau principle – electrons fill orbitals from lowest to highest energy level

Subshells

• Each princ energy level has subshells• Subshell – the shape of the probability (orbital) of e-

location s,p,d,f• s – 1 orbital• p – 3 orbitals (px,py, pz)• d – 5 orbitals• f – 7 orbitals• Pauli exclusion principle – an orbital can hold a

maximum of 2 electrons spinning in opposite directions

1s, 2s, 3s orbitals

2s

2p orbitals

d orbitals

f orbitals

Electron configuration

• To determine location of e-, use electron configuration

• Identifies number of electrons in ground state in each subshell at each energy level for that atom

Electron configuration

To figure out how many subshells are in each energy level:

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d7s 7p 7d

E- config examples

• H – 1 electron = 1s• He – 2 electrons = 2s2

• Li – 1s22s• Be – 1s22s2

• B – 1s22s22p• C - 1s22s22p2

Using the PT as a map

Orbital Box Diagrams• Orbital box diagrams – illustrated representations

of e- configuration• Boxes = orbitals• Arrows = electrons, demonstrates spin• Electrons can only be paired in opposite directions• H:

Hund’s Rule: To minimize repulsion and maintain low energy, electrons fill orbitals singly. When all orbitals are occupied by at least one e-, then electrons will pair up.

Shorthand e- configuration

1. Find the symbol for your element2. Write the symbol in brackets for the noble

gas at the far right of the proceeding horizontal row

3. Complete the rest of the e- config following that noble gas

Ex: For magnesium: [Ne] 3s2