Chapter 5 Models of the Atom

Bohr’s model… Electrons are found in specific circular paths (orbits) around the nucleus. The electrons have fixed energies called energy levels. (like rungs on a ladder) The amount of energy required to move an electron to another energy level is called a quantum.

The Quantum Mechanical model It is based on the energy and possible location of an electron. how likely it is to find an electron is described in terms of probability. (ie. Propeller blades) Based on work done by Shrodinger…

Atomic Orbitals The energy levels of electrons are labeled by principal quantum numbers (n) Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.

Atomic Orbitals

Shapes and Orientations of Orbitals 22/09/99 Shapes and Orientations of Orbitals

1s Orbital Sphere around the nucleus The one tells you that the electron is in the orbital closest to the nucleus S tells you about the shape

2s Orbital Similar to 1s except the electron is most likely in the region farther from the nucleus

p Orbitals At the first energy level there is only the 1s orbital, after the second energy level there are 2p orbitals Look like dumbbells In the three directions

Remember…. MAX NUMBER OF ELECTRONS IN AN ENERGY LEVEL MAX # OF ELECTRONS 1 2 8 3 18 4 32 5 50

Electron Configuration A detailed way of showing the order in which electrons fill in around the nucleus

Electron Configuration Symbols # of e- in sub level Electron Configuration Symbols 1s 2 Energy Level Sub Level (s, p, d, f )

We must follow 3 rules… Aufbau priciple Electrons occupy energy levels with lowest energy first.

Pauli exclusion principle If 2 electrons occupy the same energy level they must have opposite spins.

Hund’s rule… Electrons that occupy orbitals of the same energy will have the maximum number of electrons with the same spin. 2p

To start we will use orbital filling diagrams to help us with electron configurations…. Example Boron- has 5 electrons

Periodic table arrangement 22/09/99 the quantum theory helps to explain the structure of the periodic table. n - 1 indicates that the d subshell in period 4 actually starts at 3 (4 - 1 = 3).

Practice!!!

Summary: p orbitals and d orbitals 22/09/99 p orbitals look like a dumbell with 3 orientations: px, py, pz (“p sub z”). Four of the d orbitals resemble two dumbells in a clover shape. The last d orbital resembles a p orbital with a donut wrapped around the middle.

Principle Quantum # (n) 1st Quantum # Principle Quantum # (n) Specifies the energy level that the electron is on.

Specifies the shape of the sub level . 2nd Quantum # (l) Specifies the shape of the sub level .

The 3rd (m) and 4th quantum numbers (s) … Deals with the orbital within the sublevel and the spin of the electron.

Four Energy Sub-Levels Energy Level Sub-level Type of sub # of Orbitals s Sphere 2 1 p Dumbbell 6 3 d 4-Lobed 10 5 f 6-8 Lobed 14 7